A Spring Cloud application operates by creating a “bootstrap” context, which is a parent context for the main application. It is responsible for loading configuration properties from the external sources and for decrypting properties in the local external configuration files. The two contexts share an Environment, which is the source of external properties for any Spring application. By default, bootstrap properties (not bootstrap.properties but properties that are loaded during the bootstrap phase) are added with high precedence, so they cannot be overridden by local configuration.

The bootstrap context uses a different convention for locating external configuration than the main application context. Instead of application.yml (or .properties), you can use bootstrap.yml, keeping the external configuration for bootstrap and main context nicely separate. The following listing shows an example:

bootstrap.yml. 

spring:
  application:
    name: foo
  cloud:
    config:
      uri: ${SPRING_CONFIG_URI:http://localhost:8888}

If your application needs any application-specific configuration from the server, it is a good idea to set the spring.application.name (in bootstrap.yml or application.yml).

You can disable the bootstrap process completely by setting spring.cloud.bootstrap.enabled=false (for example, in system properties).

If you build an application context from SpringApplication or SpringApplicationBuilder, then the Bootstrap context is added as a parent to that context. It is a feature of Spring that child contexts inherit property sources and profiles from their parent, so the “main” application context contains additional property sources, compared to building the same context without Spring Cloud Config. The additional property sources are:

Because of the ordering rules of property sources, the “bootstrap” entries take precedence. However, note that these do not contain any data from bootstrap.yml, which has very low precedence but can be used to set defaults.

You can extend the context hierarchy by setting the parent context of any ApplicationContext you create — for example, by using its own interface or with the SpringApplicationBuilder convenience methods (parent(), child() and sibling()). The bootstrap context is the parent of the most senior ancestor that you create yourself. Every context in the hierarchy has its own “bootstrap” (possibly empty) property source to avoid promoting values inadvertently from parents down to their descendants. If there is a Config Server, every context in the hierarchy can also (in principle) have a different spring.application.name and, hence, a different remote property source. Normal Spring application context behavior rules apply to property resolution: properties from a child context override those in the parent, by name and also by property source name. (If the child has a property source with the same name as the parent, the value from the parent is not included in the child).

Note that the SpringApplicationBuilder lets you share an Environment amongst the whole hierarchy, but that is not the default. Thus, sibling contexts, in particular, do not need to have the same profiles or property sources, even though they may share common values with their parent.

The bootstrap.yml (or .properties) location can be specified by setting spring.cloud.bootstrap.name (default: bootstrap) or spring.cloud.bootstrap.location (default: empty) — for example, in System properties. Those properties behave like the spring.config.* variants with the same name. In fact, they are used to set up the bootstrap ApplicationContext by setting those properties in its Environment. If there is an active profile (from spring.profiles.active or through the Environment API in the context you are building), properties in that profile get loaded as well, the same as in a regular Spring Boot app — for example, from bootstrap-development.properties for a development profile.

The property sources that are added to your application by the bootstrap context are often “remote” (from example, from Spring Cloud Config Server). By default, they cannot be overridden locally. If you want to let your applications override the remote properties with their own System properties or config files, the remote property source has to grant it permission by setting spring.cloud.config.allowOverride=true (it does not work to set this locally). Once that flag is set, two finer-grained settings control the location of the remote properties in relation to system properties and the application’s local configuration:

The bootstrap context can be set to do anything you like by adding entries to /META-INF/spring.factories under a key named org.springframework.cloud.bootstrap.BootstrapConfiguration. This holds a comma-separated list of Spring @Configuration classes that are used to create the context. Any beans that you want to be available to the main application context for autowiring can be created here. There is a special contract for @Beans of type ApplicationContextInitializer. If you want to control the startup sequence, classes can be marked with an @Order annotation (the default order is last).

	Warning
	When adding custom BootstrapConfiguration, be careful that the classes you add are not @ComponentScanned by mistake into your “main” application context, where they might not be needed. Use a separate package name for boot configuration classes and make sure that name is not already covered by your @ComponentScan or @SpringBootApplication annotated configuration classes.

The bootstrap process ends by injecting initializers into the main SpringApplication instance (which is the normal Spring Boot startup sequence, whether it is running as a standalone application or deployed in an application server). First, a bootstrap context is created from the classes found in spring.factories. Then, all @Beans of type ApplicationContextInitializer are added to the main SpringApplication before it is started.

The default property source for external configuration added by the bootstrap process is the Spring Cloud Config Server, but you can add additional sources by adding beans of type PropertySourceLocator to the bootstrap context (through spring.factories). For instance, you can insert additional properties from a different server or from a database.

As an example, consider the following custom locator:

@Configuration
public class CustomPropertySourceLocator implements PropertySourceLocator {

    @Override
    public PropertySource<?> locate(Environment environment) {
        return new MapPropertySource("customProperty",
                Collections.<String, Object>singletonMap("property.from.sample.custom.source", "worked as intended"));
    }

}

The Environment that is passed in is the one for the ApplicationContext about to be created — in other words, the one for which we supply additional property sources for. It already has its normal Spring Boot-provided property sources, so you can use those to locate a property source specific to this Environment (for example, by keying it on spring.application.name, as is done in the default Spring Cloud Config Server property source locator).

If you create a jar with this class in it and then add a META-INF/spring.factories containing the following, the customProperty PropertySource appears in any application that includes that jar on its classpath:

org.springframework.cloud.bootstrap.BootstrapConfiguration=sample.custom.CustomPropertySourceLocator

If you are going to use Spring Boot to configure log settings than you should place this configuration in `bootstrap.[yml | properties] if you would like it to apply to all events.

	Note
	For Spring Cloud to initialize logging configuration properly you cannot use a custom prefix. For example, using custom.loggin.logpath will not be recognized by Spring Cloud when initializing the logging system.

The application listens for an EnvironmentChangeEvent and reacts to the change in a couple of standard ways (additional ApplicationListeners can be added as @Beans by the user in the normal way). When an EnvironmentChangeEvent is observed, it has a list of key values that have changed, and the application uses those to:

Note that the Config Client does not, by default, poll for changes in the Environment. Generally, we would not recommend that approach for detecting changes (although you could set it up with a @Scheduled annotation). If you have a scaled-out client application, it is better to broadcast the EnvironmentChangeEvent to all the instances instead of having them polling for changes (for example, by using the Spring Cloud Bus).

The EnvironmentChangeEvent covers a large class of refresh use cases, as long as you can actually make a change to the Environment and publish the event. Note that those APIs are public and part of core Spring). You can verify that the changes are bound to @ConfigurationProperties beans by visiting the /configprops endpoint (a normal Spring Boot Actuator feature). For instance, a DataSource can have its maxPoolSize changed at runtime (the default DataSource created by Spring Boot is an @ConfigurationProperties bean) and grow capacity dynamically. Re-binding @ConfigurationProperties does not cover another large class of use cases, where you need more control over the refresh and where you need a change to be atomic over the whole ApplicationContext. To address those concerns, we have @RefreshScope.

When there is a configuration change, a Spring @Bean that is marked as @RefreshScope gets special treatment. This feature addresses the problem of stateful beans that only get their configuration injected when they are initialized. For instance, if a DataSource has open connections when the database URL is changed via the Environment, you probably want the holders of those connections to be able to complete what they are doing. Then, the next time something borrows a connection from the pool, it gets one with the new URL.

Sometimes, it might even be mandatory to apply the @RefreshScope annotation on some beans which can be only initialized once. If a bean is "immutable", you will have to either annotate the bean with @RefreshScope or specify the classname under the property key spring.cloud.refresh.extra-refreshable.

	Important
	If you create a DataSource bean yourself and the implementation is a HikariDataSource, return the most specific type, in this case HikariDataSource. Otherwise, you will need to set spring.cloud.refresh.extra-refreshable=javax.sql.DataSource.

Refresh scope beans are lazy proxies that initialize when they are used (that is, when a method is called), and the scope acts as a cache of initialized values. To force a bean to re-initialize on the next method call, you must invalidate its cache entry.

The RefreshScope is a bean in the context and has a public refreshAll() method to refresh all beans in the scope by clearing the target cache. The /refresh endpoint exposes this functionality (over HTTP or JMX). To refresh an individual bean by name, there is also a refresh(String) method.

To expose the /refresh endpoint, you need to add following configuration to your application:

management:
  endpoints:
    web:
      exposure:
        include: refresh

Note

@RefreshScope works (technically) on an @Configuration class, but it might lead to surprising behavior. For example, it does not mean that all the @Beans defined in that class are themselves in @RefreshScope. Specifically, anything that depends on those beans cannot rely on them being updated when a refresh is initiated, unless it is itself in @RefreshScope. In that case, it is rebuilt on a refresh and its dependencies are re-injected. At that point, they are re-initialized from the refreshed @Configuration).

Spring Cloud has an Environment pre-processor for decrypting property values locally. It follows the same rules as the Config Server and has the same external configuration through encrypt.*. Thus, you can use encrypted values in the form of {cipher}* and, as long as there is a valid key, they are decrypted before the main application context gets the Environment settings. To use the encryption features in an application, you need to include Spring Security RSA in your classpath (Maven co-ordinates: "org.springframework.security:spring-security-rsa"), and you also need the full strength JCE extensions in your JVM.

If you get an exception due to "Illegal key size" and you use Sun’s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files. See the following links for more information:

Extract the files into the JDK/jre/lib/security folder for whichever version of JRE/JDK x64/x86 you use.

For a Spring Boot Actuator application, some additional management endpoints are available. You can use:

	Note
	If you disable the /actuator/restart endpoint then the /actuator/pause and /actuator/resume endpoints will also be disabled since they are just a special case of /actuator/restart.

Spring Cloud Commons provides the @EnableDiscoveryClient annotation. This looks for implementations of the DiscoveryClient interface with META-INF/spring.factories. Implementations of the Discovery Client add a configuration class to spring.factories under the org.springframework.cloud.client.discovery.EnableDiscoveryClient key. Examples of DiscoveryClient implementations include Spring Cloud Netflix Eureka, Spring Cloud Consul Discovery, and Spring Cloud Zookeeper Discovery.

By default, implementations of DiscoveryClient auto-register the local Spring Boot server with the remote discovery server. This behavior can be disabled by setting autoRegister=false in @EnableDiscoveryClient.

	Note
	@EnableDiscoveryClient is no longer required. You can put a DiscoveryClient implementation on the classpath to cause the Spring Boot application to register with the service discovery server.

Commons now provides a ServiceRegistry interface that provides methods such as register(Registration) and deregister(Registration), which let you provide custom registered services. Registration is a marker interface.

The following example shows the ServiceRegistry in use:

@Configuration
@EnableDiscoveryClient(autoRegister=false)
public class MyConfiguration {
    private ServiceRegistry registry;

    public MyConfiguration(ServiceRegistry registry) {
        this.registry = registry;
    }

    // called through some external process, such as an event or a custom actuator endpoint
    public void register() {
        Registration registration = constructRegistration();
        this.registry.register(registration);
    }
}

Each ServiceRegistry implementation has its own Registry implementation.

If you are using the ServiceRegistry interface, you are going to need to pass the correct Registry implementation for the ServiceRegistry implementation you are using.

3.2.1 ServiceRegistry Auto-Registration

By default, the ServiceRegistry implementation auto-registers the running service. To disable that behavior, you can set: * @EnableDiscoveryClient(autoRegister=false) to permanently disable auto-registration. * spring.cloud.service-registry.auto-registration.enabled=false to disable the behavior through configuration.

ServiceRegistry Auto-Registration Events

There are two events that will be fired when a service auto-registers. The first event, called InstancePreRegisteredEvent, is fired before the service is registered. The second event, called InstanceRegisteredEvent, is fired after the service is registered. You can register an ApplicationListener(s) to listen to and react to these events.

	Note
	These events will not be fired if spring.cloud.service-registry.auto-registration.enabled is set to false.

RestTemplate can be automatically configured to use ribbon. To create a load-balanced RestTemplate, create a RestTemplate @Bean and use the @LoadBalanced qualifier, as shown in the following example:

@Configuration
public class MyConfiguration {

    @LoadBalanced
    @Bean
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

public class MyClass {
    @Autowired
    private RestTemplate restTemplate;

    public String doOtherStuff() {
        String results = restTemplate.getForObject("http://stores/stores", String.class);
        return results;
    }
}

	Caution
	A RestTemplate bean is no longer created through auto-configuration. Individual applications must create it.

The URI needs to use a virtual host name (that is, a service name, not a host name). The Ribbon client is used to create a full physical address. See RibbonAutoConfiguration for details of how the RestTemplate is set up.

WebClient can be automatically configured to use the LoadBalancerClient. To create a load-balanced WebClient, create a WebClient.Builder @Bean and use the @LoadBalanced qualifier, as shown in the following example:

@Configuration
public class MyConfiguration {

	@Bean
	@LoadBalanced
	public WebClient.Builder loadBalancedWebClientBuilder() {
		return WebClient.builder();
	}
}

public class MyClass {
    @Autowired
    private WebClient.Builder webClientBuilder;

    public Mono<String> doOtherStuff() {
        return webClientBuilder.build().get().uri("http://stores/stores")
        				.retrieve().bodyToMono(String.class);
    }
}

The URI needs to use a virtual host name (that is, a service name, not a host name). The Ribbon client is used to create a full physical address.

3.4.1 Retrying Failed Requests

A load-balanced RestTemplate can be configured to retry failed requests. By default, this logic is disabled. You can enable it by adding Spring Retry to your application’s classpath. The load-balanced RestTemplate honors some of the Ribbon configuration values related to retrying failed requests. You can use client.ribbon.MaxAutoRetries, client.ribbon.MaxAutoRetriesNextServer, and client.ribbon.OkToRetryOnAllOperations properties. If you would like to disable the retry logic with Spring Retry on the classpath, you can set spring.cloud.loadbalancer.retry.enabled=false. See the Ribbon documentation for a description of what these properties do.

If you would like to implement a BackOffPolicy in your retries, you need to create a bean of type LoadBalancedRetryFactory and override the createBackOffPolicy method:

@Configuration
public class MyConfiguration {
    @Bean
    LoadBalancedRetryFactory retryFactory() {
        return new LoadBalancedRetryFactory() {
            @Override
            public BackOffPolicy createBackOffPolicy(String service) {
        		return new ExponentialBackOffPolicy();
        	}
        };
    }
}

	Note
	client in the preceding examples should be replaced with your Ribbon client’s name.

If you want to add one or more RetryListener implementations to your retry functionality, you need to create a bean of type LoadBalancedRetryListenerFactory and return the RetryListener array you would like to use for a given service, as shown in the following example:

@Configuration
public class MyConfiguration {
    @Bean
    LoadBalancedRetryListenerFactory retryListenerFactory() {
        return new LoadBalancedRetryListenerFactory() {
            @Override
            public RetryListener[] createRetryListeners(String service) {
                return new RetryListener[]{new RetryListener() {
                    @Override
                    public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) {
                        //TODO Do you business...
                        return true;
                    }

                    @Override
                     public <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) {
                        //TODO Do you business...
                    }

                    @Override
                    public <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) {
                        //TODO Do you business...
                    }
                }};
            }
        };
    }
}

If you want a RestTemplate that is not load-balanced, create a RestTemplate bean and inject it. To access the load-balanced RestTemplate, use the @LoadBalanced qualifier when you create your @Bean, as shown in the following example:\

@Configuration
public class MyConfiguration {

    @LoadBalanced
    @Bean
    RestTemplate loadBalanced() {
        return new RestTemplate();
    }

    @Primary
    @Bean
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

public class MyClass {
    @Autowired
    private RestTemplate restTemplate;

    @Autowired
    @LoadBalanced
    private RestTemplate loadBalanced;

    public String doOtherStuff() {
        return loadBalanced.getForObject("http://stores/stores", String.class);
    }

    public String doStuff() {
        return restTemplate.getForObject("http://example.com", String.class);
    }
}

	Important
	Notice the use of the @Primary annotation on the plain RestTemplate declaration in the preceding example to disambiguate the unqualified @Autowired injection.

	Tip
	If you see errors such as java.lang.IllegalArgumentException: Can not set org.springframework.web.client.RestTemplate field com.my.app.Foo.restTemplate to com.sun.proxy.$Proxy89, try injecting RestOperations or setting spring.aop.proxyTargetClass=true.

WebClient can be configured to use the LoadBalancerClient. LoadBalancerExchangeFilterFunction is auto-configured if spring-webflux is on the classpath. The following example shows how to configure a WebClient to use load balancer:

public class MyClass {
    @Autowired
    private LoadBalancerExchangeFilterFunction lbFunction;

    public Mono<String> doOtherStuff() {
        return WebClient.builder().baseUrl("http://stores")
            .filter(lbFunction)
            .build()
            .get()
            .uri("/stores")
            .retrieve()
            .bodyToMono(String.class);
    }
}

The URI needs to use a virtual host name (that is, a service name, not a host name). The LoadBalancerClient is used to create a full physical address.

Sometimes, it is useful to ignore certain named network interfaces so that they can be excluded from Service Discovery registration (for example, when running in a Docker container). A list of regular expressions can be set to cause the desired network interfaces to be ignored. The following configuration ignores the docker0 interface and all interfaces that start with veth:

application.yml. 

spring:
  cloud:
    inetutils:
      ignoredInterfaces:
        - docker0
        - veth.*

You can also force the use of only specified network addresses by using a list of regular expressions, as shown in the following example:

bootstrap.yml. 

spring:
  cloud:
    inetutils:
      preferredNetworks:
        - 192.168
        - 10.0

You can also force the use of only site-local addresses, as shown in the following example: .application.yml

spring:
  cloud:
    inetutils:
      useOnlySiteLocalInterfaces: true

See Inet4Address.html.isSiteLocalAddress() for more details about what constitutes a site-local address.

Spring Cloud Commons provides beans for creating both Apache HTTP clients (ApacheHttpClientFactory) and OK HTTP clients (OkHttpClientFactory). The OkHttpClientFactory bean is created only if the OK HTTP jar is on the classpath. In addition, Spring Cloud Commons provides beans for creating the connection managers used by both clients: ApacheHttpClientConnectionManagerFactory for the Apache HTTP client and OkHttpClientConnectionPoolFactory for the OK HTTP client. If you would like to customize how the HTTP clients are created in downstream projects, you can provide your own implementation of these beans. In addition, if you provide a bean of type HttpClientBuilder or OkHttpClient.Builder, the default factories use these builders as the basis for the builders returned to downstream projects. You can also disable the creation of these beans by setting spring.cloud.httpclientfactories.apache.enabled or spring.cloud.httpclientfactories.ok.enabled to false.

Spring Cloud Commons provides a /features actuator endpoint. This endpoint returns features available on the classpath and whether they are enabled. The information returned includes the feature type, name, version, and vendor.

@Bean
public HasFeatures commonsFeatures() {
  return HasFeatures.abstractFeatures(DiscoveryClient.class, LoadBalancerClient.class);
}

@Bean
public HasFeatures consulFeatures() {
  return HasFeatures.namedFeatures(
    new NamedFeature("Spring Cloud Bus", ConsulBusAutoConfiguration.class),
    new NamedFeature("Circuit Breaker", HystrixCommandAspect.class));
}

@Bean
HasFeatures localFeatures() {
  return HasFeatures.builder()
      .abstractFeature(Foo.class)
      .namedFeature(new NamedFeature("Bar Feature", Bar.class))
      .abstractFeature(Baz.class)
      .build();
}

Due to the fact that some users have problem with setting up Spring Cloud application, we’ve decided to add a compatibility verification mechanism. It will break if your current setup is not compatible with Spring Cloud requirements, together with a report, showing what exactly went wrong.

At the moment we verify which version of Spring Boot is added to your classpath.

Example of a report

***************************
APPLICATION FAILED TO START
***************************

Description:

Your project setup is incompatible with our requirements due to following reasons:

- Spring Boot [2.1.0.RELEASE] is not compatible with this Spring Cloud release train


Action:

Consider applying the following actions:

- Change Spring Boot version to one of the following versions [1.2.x, 1.3.x] .
You can find the latest Spring Boot versions here [https://spring.io/projects/spring-boot#learn].
If you want to learn more about the Spring Cloud Release train compatibility, you can visit this page [https://spring.io/projects/spring-cloud#overview] and check the [Release Trains] section.

In order to disable this feature, set spring.cloud.compatibility-verifier.enabled to false. If you want to override the compatible Spring Boot versions, just set the spring.cloud.compatibility-verifier.compatible-boot-versions property with a comma separated list of compatible Spring Boot versions.

To use these features in an application, you can build it as a Spring Boot application that depends on spring-cloud-config-client (for an example, see the test cases for the config-client or the sample application). The most convenient way to add the dependency is with a Spring Boot starter org.springframework.cloud:spring-cloud-starter-config. There is also a parent pom and BOM (spring-cloud-starter-parent) for Maven users and a Spring IO version management properties file for Gradle and Spring CLI users. The following example shows a typical Maven configuration:

pom.xml. 

   <parent>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-parent</artifactId>
       <version>{spring-boot-docs-version}</version>
       <relativePath /> <!-- lookup parent from repository -->
   </parent>

<dependencyManagement>
	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-dependencies</artifactId>
			<version>{spring-cloud-version}</version>
			<type>pom</type>
			<scope>import</scope>
		</dependency>
	</dependencies>
</dependencyManagement>

<dependencies>
	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-starter-config</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-test</artifactId>
		<scope>test</scope>
	</dependency>
</dependencies>

<build>
	<plugins>
           <plugin>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-maven-plugin</artifactId>
           </plugin>
	</plugins>
</build>

   <!-- repositories also needed for snapshots and milestones -->

Now you can create a standard Spring Boot application, such as the following HTTP server:

@SpringBootApplication
@RestController
public class Application {

    @RequestMapping("/")
    public String home() {
        return "Hello World!";
    }

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

When this HTTP server runs, it picks up the external configuration from the default local config server (if it is running) on port 8888. To modify the startup behavior, you can change the location of the config server by using bootstrap.properties (similar to application.properties but for the bootstrap phase of an application context), as shown in the following example:

spring.cloud.config.uri: http://myconfigserver.com

By default, if no application name is set, application will be used. To modify the name, the following property can be added to the bootstrap.properties file:

spring.application.name: myapp

	Note
	When setting the property ${spring.application.name} do not prefix your app name with the reserved word application- to prevent issues resolving the correct property source.

The bootstrap properties show up in the /env endpoint as a high-priority property source, as shown in the following example.

$ curl localhost:8080/env
{
  "profiles":[],
  "configService:https://github.com/spring-cloud-samples/config-repo/bar.properties":{"foo":"bar"},
  "servletContextInitParams":{},
  "systemProperties":{...},
  ...
}

A property source called ``configService:<URL of remote repository>/<file name> contains the foo property with a value of bar and is highest priority.

	Note
	The URL in the property source name is the git repository, not the config server URL.

Where should you store the configuration data for the Config Server? The strategy that governs this behaviour is the EnvironmentRepository, serving Environment objects. This Environment is a shallow copy of the domain from the Spring Environment (including propertySources as the main feature). The Environment resources are parametrized by three variables:

Repository implementations generally behave like a Spring Boot application, loading configuration files from a spring.config.name equal to the {application} parameter, and spring.profiles.active equal to the {profiles} parameter. Precedence rules for profiles are also the same as in a regular Spring Boot application: Active profiles take precedence over defaults, and, if there are multiple profiles, the last one wins (similar to adding entries to a Map).

The following sample client application has this bootstrap configuration:

bootstrap.yml. 

spring:
  application:
    name: foo
  profiles:
    active: dev,mysql

(As usual with a Spring Boot application, these properties could also be set by environment variables or command line arguments).

If the repository is file-based, the server creates an Environment from application.yml (shared between all clients) and foo.yml (with foo.yml taking precedence). If the YAML files have documents inside them that point to Spring profiles, those are applied with higher precedence (in order of the profiles listed). If there are profile-specific YAML (or properties) files, these are also applied with higher precedence than the defaults. Higher precedence translates to a PropertySource listed earlier in the Environment. (These same rules apply in a standalone Spring Boot application.)

You can set spring.cloud.config.server.accept-empty to false so that Server would return a HTTP 404 status, if the application is not found.By default, this flag is set to true.

5.1.1 Git Backend

The default implementation of EnvironmentRepository uses a Git backend, which is very convenient for managing upgrades and physical environments and for auditing changes. To change the location of the repository, you can set the spring.cloud.config.server.git.uri configuration property in the Config Server (for example in application.yml). If you set it with a file: prefix, it should work from a local repository so that you can get started quickly and easily without a server. However, in that case, the server operates directly on the local repository without cloning it (it does not matter if it is not bare because the Config Server never makes changes to the "remote" repository). To scale the Config Server up and make it highly available, you need to have all instances of the server pointing to the same repository, so only a shared file system would work. Even in that case, it is better to use the ssh: protocol for a shared filesystem repository, so that the server can clone it and use a local working copy as a cache.

This repository implementation maps the {label} parameter of the HTTP resource to a git label (commit id, branch name, or tag). If the git branch or tag name contains a slash (/), then the label in the HTTP URL should instead be specified with the special string (_) (to avoid ambiguity with other URL paths). For example, if the label is foo/bar, replacing the slash would result in the following label: foo(_)bar. The inclusion of the special string (_) can also be applied to the {application} parameter. If you use a command-line client such as curl, be careful with the brackets in the URL — you should escape them from the shell with single quotes ('').

Skipping SSL Certificate Validation

The configuration server’s validation of the Git server’s SSL certificate can be disabled by setting the git.skipSslValidation property to true (default is false).

spring:
  cloud:
    config:
      server:
        git:
          uri: https://example.com/my/repo
          skipSslValidation: true

Setting HTTP Connection Timeout

You can configure the time, in seconds, that the configuration server will wait to acquire an HTTP connection. Use the git.timeout property.

spring:
  cloud:
    config:
      server:
        git:
          uri: https://example.com/my/repo
          timeout: 4

Placeholders in Git URI

Spring Cloud Config Server supports a git repository URL with placeholders for the {application} and {profile} (and {label} if you need it, but remember that the label is applied as a git label anyway). So you can support a “one repository per application” policy by using a structure similar to the following:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/myorg/{application}

You can also support a “one repository per profile” policy by using a similar pattern but with {profile}.

Additionally, using the special string "(_)" within your {application} parameters can enable support for multiple organizations, as shown in the following example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/{application}

where {application} is provided at request time in the following format: organization(_)application.

Pattern Matching and Multiple Repositories

Spring Cloud Config also includes support for more complex requirements with pattern matching on the application and profile name. The pattern format is a comma-separated list of {application}/{profile} names with wildcards (note that a pattern beginning with a wildcard may need to be quoted), as shown in the following example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          repos:
            simple: https://github.com/simple/config-repo
            special:
              pattern: special*/dev*,*special*/dev*
              uri: https://github.com/special/config-repo
            local:
              pattern: local*
              uri: file:/home/configsvc/config-repo

If {application}/{profile} does not match any of the patterns, it uses the default URI defined under spring.cloud.config.server.git.uri. In the above example, for the “simple” repository, the pattern is simple/* (it only matches one application named simple in all profiles). The “local” repository matches all application names beginning with local in all profiles (the /* suffix is added automatically to any pattern that does not have a profile matcher).

	Note
	The “one-liner” short cut used in the “simple” example can be used only if the only property to be set is the URI. If you need to set anything else (credentials, pattern, and so on) you need to use the full form.

The pattern property in the repo is actually an array, so you can use a YAML array (or [0], [1], etc. suffixes in properties files) to bind to multiple patterns. You may need to do so if you are going to run apps with multiple profiles, as shown in the following example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          repos:
            development:
              pattern:
                - '*/development'
                - '*/staging'
              uri: https://github.com/development/config-repo
            staging:
              pattern:
                - '*/qa'
                - '*/production'
              uri: https://github.com/staging/config-repo

	Note
	Spring Cloud guesses that a pattern containing a profile that does not end in * implies that you actually want to match a list of profiles starting with this pattern (so */staging is a shortcut for ["*/staging", "*/staging,*"], and so on). This is common where, for instance, you need to run applications in the “development” profile locally but also the “cloud” profile remotely.

Every repository can also optionally store config files in sub-directories, and patterns to search for those directories can be specified as searchPaths. The following example shows a config file at the top level:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          searchPaths: foo,bar*

In the preceding example, the server searches for config files in the top level and in the foo/ sub-directory and also any sub-directory whose name begins with bar.

By default, the server clones remote repositories when configuration is first requested. The server can be configured to clone the repositories at startup, as shown in the following top-level example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://git/common/config-repo.git
          repos:
            team-a:
                pattern: team-a-*
                cloneOnStart: true
                uri: http://git/team-a/config-repo.git
            team-b:
                pattern: team-b-*
                cloneOnStart: false
                uri: http://git/team-b/config-repo.git
            team-c:
                pattern: team-c-*
                uri: http://git/team-a/config-repo.git

In the preceding example, the server clones team-a’s config-repo on startup, before it accepts any requests. All other repositories are not cloned until configuration from the repository is requested.

Note

Setting a repository to be cloned when the Config Server starts up can help to identify a misconfigured configuration source (such as an invalid repository URI) quickly, while the Config Server is starting up. With cloneOnStart not enabled for a configuration source, the Config Server may start successfully with a misconfigured or invalid configuration source and not detect an error until an application requests configuration from that configuration source.

Authentication

To use HTTP basic authentication on the remote repository, add the username and password properties separately (not in the URL), as shown in the following example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          username: trolley
          password: strongpassword

If you do not use HTTPS and user credentials, SSH should also work out of the box when you store keys in the default directories (~/.ssh) and the URI points to an SSH location, such as [email protected]:configuration/cloud-configuration. It is important that an entry for the Git server be present in the ~/.ssh/known_hosts file and that it is in ssh-rsa format. Other formats (such as ecdsa-sha2-nistp256) are not supported. To avoid surprises, you should ensure that only one entry is present in the known_hosts file for the Git server and that it matches the URL you provided to the config server. If you use a hostname in the URL, you want to have exactly that (not the IP) in the known_hosts file. The repository is accessed by using JGit, so any documentation you find on that should be applicable. HTTPS proxy settings can be set in ~/.git/config or (in the same way as for any other JVM process) with system properties (-Dhttps.proxyHost and -Dhttps.proxyPort).

	Tip
	If you do not know where your ~/.git directory is, use git config --global to manipulate the settings (for example, git config --global http.sslVerify false).

Authentication with AWS CodeCommit

Spring Cloud Config Server also supports AWS CodeCommit authentication. AWS CodeCommit uses an authentication helper when using Git from the command line. This helper is not used with the JGit library, so a JGit CredentialProvider for AWS CodeCommit is created if the Git URI matches the AWS CodeCommit pattern. AWS CodeCommit URIs follow this pattern://git-codecommit.${AWS_REGION}.amazonaws.com/${repopath}.

If you provide a username and password with an AWS CodeCommit URI, they must be the AWS accessKeyId and secretAccessKey that provide access to the repository. If you do not specify a username and password, the accessKeyId and secretAccessKey are retrieved by using the AWS Default Credential Provider Chain.

If your Git URI matches the CodeCommit URI pattern (shown earlier), you must provide valid AWS credentials in the username and password or in one of the locations supported by the default credential provider chain. AWS EC2 instances may use IAM Roles for EC2 Instances.

	Note
	The aws-java-sdk-core jar is an optional dependency. If the aws-java-sdk-core jar is not on your classpath, the AWS Code Commit credential provider is not created, regardless of the git server URI.

Git SSH configuration using properties

By default, the JGit library used by Spring Cloud Config Server uses SSH configuration files such as ~/.ssh/known_hosts and /etc/ssh/ssh_config when connecting to Git repositories by using an SSH URI. In cloud environments such as Cloud Foundry, the local filesystem may be ephemeral or not easily accessible. For those cases, SSH configuration can be set by using Java properties. In order to activate property-based SSH configuration, the spring.cloud.config.server.git.ignoreLocalSshSettings property must be set to true, as shown in the following example:

  spring:
    cloud:
      config:
        server:
          git:
            uri: git@gitserver.com:team/repo1.git
            ignoreLocalSshSettings: true
            hostKey: someHostKey
            hostKeyAlgorithm: ssh-rsa
            privateKey: |
                         -----BEGIN RSA PRIVATE KEY-----
                         MIIEpgIBAAKCAQEAx4UbaDzY5xjW6hc9jwN0mX33XpTDVW9WqHp5AKaRbtAC3DqX
                         IXFMPgw3K45jxRb93f8tv9vL3rD9CUG1Gv4FM+o7ds7FRES5RTjv2RT/JVNJCoqF
                         ol8+ngLqRZCyBtQN7zYByWMRirPGoDUqdPYrj2yq+ObBBNhg5N+hOwKjjpzdj2Ud
                         1l7R+wxIqmJo1IYyy16xS8WsjyQuyC0lL456qkd5BDZ0Ag8j2X9H9D5220Ln7s9i
                         oezTipXipS7p7Jekf3Ywx6abJwOmB0rX79dV4qiNcGgzATnG1PkXxqt76VhcGa0W
                         DDVHEEYGbSQ6hIGSh0I7BQun0aLRZojfE3gqHQIDAQABAoIBAQCZmGrk8BK6tXCd
                         fY6yTiKxFzwb38IQP0ojIUWNrq0+9Xt+NsypviLHkXfXXCKKU4zUHeIGVRq5MN9b
                         BO56/RrcQHHOoJdUWuOV2qMqJvPUtC0CpGkD+valhfD75MxoXU7s3FK7yjxy3rsG
                         EmfA6tHV8/4a5umo5TqSd2YTm5B19AhRqiuUVI1wTB41DjULUGiMYrnYrhzQlVvj
                         5MjnKTlYu3V8PoYDfv1GmxPPh6vlpafXEeEYN8VB97e5x3DGHjZ5UrurAmTLTdO8
                         +AahyoKsIY612TkkQthJlt7FJAwnCGMgY6podzzvzICLFmmTXYiZ/28I4BX/mOSe
                         pZVnfRixAoGBAO6Uiwt40/PKs53mCEWngslSCsh9oGAaLTf/XdvMns5VmuyyAyKG
                         ti8Ol5wqBMi4GIUzjbgUvSUt+IowIrG3f5tN85wpjQ1UGVcpTnl5Qo9xaS1PFScQ
                         xrtWZ9eNj2TsIAMp/svJsyGG3OibxfnuAIpSXNQiJPwRlW3irzpGgVx/AoGBANYW
                         dnhshUcEHMJi3aXwR12OTDnaLoanVGLwLnkqLSYUZA7ZegpKq90UAuBdcEfgdpyi
                         PhKpeaeIiAaNnFo8m9aoTKr+7I6/uMTlwrVnfrsVTZv3orxjwQV20YIBCVRKD1uX
                         VhE0ozPZxwwKSPAFocpyWpGHGreGF1AIYBE9UBtjAoGBAI8bfPgJpyFyMiGBjO6z
                         FwlJc/xlFqDusrcHL7abW5qq0L4v3R+FrJw3ZYufzLTVcKfdj6GelwJJO+8wBm+R
                         gTKYJItEhT48duLIfTDyIpHGVm9+I1MGhh5zKuCqIhxIYr9jHloBB7kRm0rPvYY4
                         VAykcNgyDvtAVODP+4m6JvhjAoGBALbtTqErKN47V0+JJpapLnF0KxGrqeGIjIRV
                         cYA6V4WYGr7NeIfesecfOC356PyhgPfpcVyEztwlvwTKb3RzIT1TZN8fH4YBr6Ee
                         KTbTjefRFhVUjQqnucAvfGi29f+9oE3Ei9f7wA+H35ocF6JvTYUsHNMIO/3gZ38N
                         CPjyCMa9AoGBAMhsITNe3QcbsXAbdUR00dDsIFVROzyFJ2m40i4KCRM35bC/BIBs
                         q0TY3we+ERB40U8Z2BvU61QuwaunJ2+uGadHo58VSVdggqAo0BSkH58innKKt96J
                         69pcVH/4rmLbXdcmNYGm6iu+MlPQk4BUZknHSmVHIFdJ0EPupVaQ8RHT
                         -----END RSA PRIVATE KEY-----

The following table describes the SSH configuration properties.

Table 5.1. SSH Configuration Properties

Property Name	Remarks
ignoreLocalSshSettings	If true, use property-based instead of file-based SSH config. Must be set at as spring.cloud.config.server.git.ignoreLocalSshSettings, not inside a repository definition.
privateKey	Valid SSH private key. Must be set if ignoreLocalSshSettings is true and Git URI is SSH format.
hostKey	Valid SSH host key. Must be set if hostKeyAlgorithm is also set.
hostKeyAlgorithm	One of ssh-dss, ssh-rsa, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, or ecdsa-sha2-nistp521. Must be set if hostKey is also set.
strictHostKeyChecking	true or false. If false, ignore errors with host key.
knownHostsFile	Location of custom .known_hosts file.
preferredAuthentications	Override server authentication method order. This should allow for evading login prompts if server has keyboard-interactive authentication before the publickey method.

Placeholders in Git Search Paths

Spring Cloud Config Server also supports a search path with placeholders for the {application} and {profile} (and {label} if you need it), as shown in the following example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          searchPaths: '{application}'

The preceding listing causes a search of the repository for files in the same name as the directory (as well as the top level). Wildcards are also valid in a search path with placeholders (any matching directory is included in the search).

Force pull in Git Repositories

As mentioned earlier, Spring Cloud Config Server makes a clone of the remote git repository in case the local copy gets dirty (for example, folder content changes by an OS process) such that Spring Cloud Config Server cannot update the local copy from remote repository.

To solve this issue, there is a force-pull property that makes Spring Cloud Config Server force pull from the remote repository if the local copy is dirty, as shown in the following example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          force-pull: true

If you have a multiple-repositories configuration, you can configure the force-pull property per repository, as shown in the following example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://git/common/config-repo.git
          force-pull: true
          repos:
            team-a:
                pattern: team-a-*
                uri: http://git/team-a/config-repo.git
                force-pull: true
            team-b:
                pattern: team-b-*
                uri: http://git/team-b/config-repo.git
                force-pull: true
            team-c:
                pattern: team-c-*
                uri: http://git/team-a/config-repo.git

	Note
	The default value for force-pull property is false.

Deleting untracked branches in Git Repositories

As Spring Cloud Config Server has a clone of the remote git repository after check-outing branch to local repo (e.g fetching properties by label) it will keep this branch forever or till the next server restart (which creates new local repo). So there could be a case when remote branch is deleted but local copy of it is still available for fetching. And if Spring Cloud Config Server client service starts with --spring.cloud.config.label=deletedRemoteBranch,master it will fetch properties from deletedRemoteBranch local branch, but not from master.

In order to keep local repository branches clean and up to remote - deleteUntrackedBranches property could be set. It will make Spring Cloud Config Server force delete untracked branches from local repository. Example:

spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          deleteUntrackedBranches: true

	Note
	The default value for deleteUntrackedBranches property is false.

Git Refresh Rate

You can control how often the config server will fetch updated configuration data from your Git backend by using spring.cloud.config.server.git.refreshRate. The value of this property is specified in seconds. By default the value is 0, meaning the config server will fetch updated configuration from the Git repo every time it is requested.

5.1.2 Version Control Backend Filesystem Use

Warning

With VCS-based backends (git, svn), files are checked out or cloned to the local filesystem. By default, they are put in the system temporary directory with a prefix of config-repo-. On linux, for example, it could be /tmp/config-repo-<randomid>. Some operating systems routinely clean out temporary directories. This can lead to unexpected behavior, such as missing properties. To avoid this problem, change the directory that Config Server uses by setting spring.cloud.config.server.git.basedir or spring.cloud.config.server.svn.basedir to a directory that does not reside in the system temp structure.

5.1.3 File System Backend

There is also a “native” profile in the Config Server that does not use Git but loads the config files from the local classpath or file system (any static URL you want to point to with spring.cloud.config.server.native.searchLocations). To use the native profile, launch the Config Server with spring.profiles.active=native.

	Note
	Remember to use the file: prefix for file resources (the default without a prefix is usually the classpath). As with any Spring Boot configuration, you can embed ${}-style environment placeholders, but remember that absolute paths in Windows require an extra / (for example, file:///${user.home}/config-repo).

	Warning
	The default value of the searchLocations is identical to a local Spring Boot application (that is, [classpath:/, classpath:/config, file:./, file:./config]). This does not expose the application.properties from the server to all clients, because any property sources present in the server are removed before being sent to the client.

	Tip
	A filesystem backend is great for getting started quickly and for testing. To use it in production, you need to be sure that the file system is reliable and shared across all instances of the Config Server.

The search locations can contain placeholders for {application}, {profile}, and {label}. In this way, you can segregate the directories in the path and choose a strategy that makes sense for you (such as subdirectory per application or subdirectory per profile).

If you do not use placeholders in the search locations, this repository also appends the {label} parameter of the HTTP resource to a suffix on the search path, so properties files are loaded from each search location and a subdirectory with the same name as the label (the labelled properties take precedence in the Spring Environment). Thus, the default behaviour with no placeholders is the same as adding a search location ending with /{label}/. For example, file:/tmp/config is the same as file:/tmp/config,file:/tmp/config/{label}. This behavior can be disabled by setting spring.cloud.config.server.native.addLabelLocations=false.

5.1.4 Vault Backend

Spring Cloud Config Server also supports Vault as a backend.

Vault is a tool for securely accessing secrets. A secret is anything that to which you want to tightly control access, such as API keys, passwords, certificates, and other sensitive information. Vault provides a unified interface to any secret while providing tight access control and recording a detailed audit log.

For more information on Vault, see the Vault quick start guide.

To enable the config server to use a Vault backend, you can run your config server with the vault profile. For example, in your config server’s application.properties, you can add spring.profiles.active=vault.

By default, the config server assumes that your Vault server runs at http://127.0.0.1:8200. It also assumes that the name of backend is secret and the key is application. All of these defaults can be configured in your config server’s application.properties. The following table describes configurable Vault properties:

Name	Default Value
host	127.0.0.1
port	8200
scheme	http
backend	secret
defaultKey	application
profileSeparator	,
kvVersion	1
skipSslValidation	false
timeout	5
namespace	null

	Important
	All of the properties in the preceding table must be prefixed with spring.cloud.config.server.vault or placed in the correct Vault section of a composite configuration.

All configurable properties can be found in org.springframework.cloud.config.server.environment.VaultEnvironmentProperties.

Vault 0.10.0 introduced a versioned key-value backend (k/v backend version 2) that exposes a different API than earlier versions, it now requires a data/ between the mount path and the actual context path and wraps secrets in a data object. Setting kvVersion=2 will take this into account.

Optionally, there is support for the Vault Enterprise X-Vault-Namespace header. To have it sent to Vault set the namespace property.

With your config server running, you can make HTTP requests to the server to retrieve values from the Vault backend. To do so, you need a token for your Vault server.

First, place some data in you Vault, as shown in the following example:

$ vault kv put secret/application foo=bar baz=bam
$ vault kv put secret/myapp foo=myappsbar

Second, make an HTTP request to your config server to retrieve the values, as shown in the following example:

$ curl -X "GET" "http://localhost:8888/myapp/default" -H "X-Config-Token: yourtoken"

You should see a response similar to the following:

{
   "name":"myapp",
   "profiles":[
      "default"
   ],
   "label":null,
   "version":null,
   "state":null,
   "propertySources":[
      {
         "name":"vault:myapp",
         "source":{
            "foo":"myappsbar"
         }
      },
      {
         "name":"vault:application",
         "source":{
            "baz":"bam",
            "foo":"bar"
         }
      }
   ]
}

Multiple Properties Sources

When using Vault, you can provide your applications with multiple properties sources. For example, assume you have written data to the following paths in Vault:

secret/myApp,dev
secret/myApp
secret/application,dev
secret/application

Properties written to secret/application are available to all applications using the Config Server. An application with the name, myApp, would have any properties written to secret/myApp and secret/application available to it. When myApp has the dev profile enabled, properties written to all of the above paths would be available to it, with properties in the first path in the list taking priority over the others.

spring:
  profiles:
    active: git
  cloud:
    config:
      server:
        git:
          uri: https://github.com/spring-cloud-samples/config-repo
          proxy:
            https:
              host: my-proxy.host.io
              password: myproxypassword
              port: '3128'
              username: myproxyusername
              nonProxyHosts: example.com

5.1.6 Sharing Configuration With All Applications

Sharing configuration between all applications varies according to which approach you take, as described in the following topics:

• the section called “File Based Repositories”
• the section called “Vault Server”

File Based Repositories

With file-based (git, svn, and native) repositories, resources with file names in application* (application.properties, application.yml, application-*.properties, and so on) are shared between all client applications. You can use resources with these file names to configure global defaults and have them be overridden by application-specific files as necessary.

The #_property_overrides[property overrides] feature can also be used for setting global defaults, with placeholders applications allowed to override them locally.

	Tip
	With the “native” profile (a local file system backend) , you should use an explicit search location that is not part of the server’s own configuration. Otherwise, the application* resources in the default search locations get removed because they are part of the server.

Vault Server

When using Vault as a backend, you can share configuration with all applications by placing configuration in secret/application. For example, if you run the following Vault command, all applications using the config server will have the properties foo and baz available to them:

$ vault write secret/application foo=bar baz=bam

5.1.8 CredHub Backend

Spring Cloud Config Server supports CredHub as a backend for configuration properties. You can enable this feature by adding a dependency to Spring CredHub.

pom.xml. 

<dependencies>
	<dependency>
		<groupId>org.springframework.credhub</groupId>
		<artifactId>spring-credhub-starter</artifactId>
	</dependency>
</dependencies>

The following configuration uses mutual TLS to access a CredHub:

spring:
  profiles:
    active: credhub
  cloud:
    config:
      server:
        credhub:
          url: https://credhub:8844

The properties should be stored as JSON, such as:

credhub set --name "/demo-app/default/master/toggles" --type=json
value: {"toggle.button": "blue", "toggle.link": "red"}

credhub set --name "/demo-app/default/master/abs" --type=json
value: {"marketing.enabled": true, "external.enabled": false}

All client applications with the name spring.cloud.config.name=demo-app will have the following properties available to them:

{
    toggle.button: "blue",
    toggle.link: "red",
    marketing.enabled: true,
    external.enabled: false
}

	Note
	When no profile is specified default will be used and when no label is specified master will be used as a default value.

OAuth 2.0

You can authenticate with OAuth 2.0 using UAA as a provider.

pom.xml. 

<dependencies>
	<dependency>
		<groupId>org.springframework.security</groupId>
		<artifactId>spring-security-config</artifactId>
	</dependency>
	<dependency>
		<groupId>org.springframework.security</groupId>
		<artifactId>spring-security-oauth2-client</artifactId>
	</dependency>
</dependencies>

The following configuration uses OAuth 2.0 and UAA to access a CredHub:

spring:
  profiles:
    active: credhub
  cloud:
    config:
      server:
        credhub:
          url: https://credhub:8844
          oauth2:
            registration-id: credhub-client
  security:
    oauth2:
      client:
        registration:
          credhub-client:
            provider: uaa
            client-id: credhub_config_server
            client-secret: asecret
            authorization-grant-type: client_credentials
        provider:
          uaa:
            token-uri: https://uaa:8443/oauth/token

	Note
	The used UAA client-id should have credhub.read as scope.

5.1.9 Composite Environment Repositories

In some scenarios, you may wish to pull configuration data from multiple environment repositories. To do so, you can enable the composite profile in your configuration server’s application properties or YAML file. If, for example, you want to pull configuration data from a Subversion repository as well as two Git repositories, you can set the following properties for your configuration server:

spring:
  profiles:
    active: composite
  cloud:
    config:
      server:
        composite:
        -
          type: svn
          uri: file:///path/to/svn/repo
        -
          type: git
          uri: file:///path/to/rex/git/repo
        -
          type: git
          uri: file:///path/to/walter/git/repo

Using this configuration, precedence is determined by the order in which repositories are listed under the composite key. In the above example, the Subversion repository is listed first, so a value found in the Subversion repository will override values found for the same property in one of the Git repositories. A value found in the rex Git repository will be used before a value found for the same property in the walter Git repository.

If you want to pull configuration data only from repositories that are each of distinct types, you can enable the corresponding profiles, rather than the composite profile, in your configuration server’s application properties or YAML file. If, for example, you want to pull configuration data from a single Git repository and a single HashiCorp Vault server, you can set the following properties for your configuration server:

spring:
  profiles:
    active: git, vault
  cloud:
    config:
      server:
        git:
          uri: file:///path/to/git/repo
          order: 2
        vault:
          host: 127.0.0.1
          port: 8200
          order: 1

Using this configuration, precedence can be determined by an order property. You can use the order property to specify the priority order for all your repositories. The lower the numerical value of the order property, the higher priority it has. The priority order of a repository helps resolve any potential conflicts between repositories that contain values for the same properties.

	Note
	If your composite environment includes a Vault server as in the previous example, you must include a Vault token in every request made to the configuration server. See Vault Backend.

	Note
	Any type of failure when retrieving values from an environment repository results in a failure for the entire composite environment.

	Note
	When using a composite environment, it is important that all repositories contain the same labels. If you have an environment similar to those in the preceding examples and you request configuration data with the master label but the Subversion repository does not contain a branch called master, the entire request fails.

Custom Composite Environment Repositories

In addition to using one of the environment repositories from Spring Cloud, you can also provide your own EnvironmentRepository bean to be included as part of a composite environment. To do so, your bean must implement the EnvironmentRepository interface. If you want to control the priority of your custom EnvironmentRepository within the composite environment, you should also implement the Ordered interface and override the getOrdered method. If you do not implement the Ordered interface, your EnvironmentRepository is given the lowest priority.

5.1.10 Property Overrides

The Config Server has an “overrides” feature that lets the operator provide configuration properties to all applications. The overridden properties cannot be accidentally changed by the application with the normal Spring Boot hooks. To declare overrides, add a map of name-value pairs to spring.cloud.config.server.overrides, as shown in the following example:

spring:
  cloud:
    config:
      server:
        overrides:
          foo: bar

The preceding examples causes all applications that are config clients to read foo=bar, independent of their own configuration.

	Note
	A configuration system cannot force an application to use configuration data in any particular way. Consequently, overrides are not enforceable. However, they do provide useful default behavior for Spring Cloud Config clients.

	Tip
	Normally, Spring environment placeholders with ${} can be escaped (and resolved on the client) by using backslash (\) to escape the $ or the {. For example, \${app.foo:bar} resolves to bar, unless the app provides its own app.foo.

	Note
	In YAML, you do not need to escape the backslash itself. However, in properties files, you do need to escape the backslash, when you configure the overrides on the server.

You can change the priority of all overrides in the client to be more like default values, letting applications supply their own values in environment variables or System properties, by setting the spring.cloud.config.overrideNone=true flag (the default is false) in the remote repository.

Config Server comes with a Health Indicator that checks whether the configured EnvironmentRepository is working. By default, it asks the EnvironmentRepository for an application named app, the default profile, and the default label provided by the EnvironmentRepository implementation.

You can configure the Health Indicator to check more applications along with custom profiles and custom labels, as shown in the following example:

spring:
  cloud:
    config:
      server:
        health:
          repositories:
            myservice:
              label: mylabel
            myservice-dev:
              name: myservice
              profiles: development

You can disable the Health Indicator by setting spring.cloud.config.server.health.enabled=false.

You can secure your Config Server in any way that makes sense to you (from physical network security to OAuth2 bearer tokens), because Spring Security and Spring Boot offer support for many security arrangements.

To use the default Spring Boot-configured HTTP Basic security, include Spring Security on the classpath (for example, through spring-boot-starter-security). The default is a username of user and a randomly generated password. A random password is not useful in practice, so we recommend you configure the password (by setting spring.security.user.password) and encrypt it (see below for instructions on how to do that).

Important

To use the encryption and decryption features you need the full-strength JCE installed in your JVM (it is not included by default). You can download the “Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files” from Oracle and follow the installation instructions (essentially, you need to replace the two policy files in the JRE lib/security directory with the ones that you downloaded).

If the remote property sources contain encrypted content (values starting with {cipher}), they are decrypted before sending to clients over HTTP. The main advantage of this setup is that the property values need not be in plain text when they are “at rest” (for example, in a git repository). If a value cannot be decrypted, it is removed from the property source and an additional property is added with the same key but prefixed with invalid and a value that means “not applicable” (usually <n/a>). This is largely to prevent cipher text being used as a password and accidentally leaking.

If you set up a remote config repository for config client applications, it might contain an application.yml similar to the following:

application.yml. 

spring:
  datasource:
    username: dbuser
    password: '{cipher}FKSAJDFGYOS8F7GLHAKERGFHLSAJ'

Encrypted values in a .properties file must not be wrapped in quotes. Otherwise, the value is not decrypted. The following example shows values that would work:

application.properties. 

spring.datasource.username: dbuser
spring.datasource.password: {cipher}FKSAJDFGYOS8F7GLHAKERGFHLSAJ

You can safely push this plain text to a shared git repository, and the secret password remains protected.

The server also exposes /encrypt and /decrypt endpoints (on the assumption that these are secured and only accessed by authorized agents). If you edit a remote config file, you can use the Config Server to encrypt values by POSTing to the /encrypt endpoint, as shown in the following example:

$ curl localhost:8888/encrypt -d mysecret
682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda

	Note
	If the value you encrypt has characters in it that need to be URL encoded, you should use the --data-urlencode option to curl to make sure they are encoded properly.

	Tip
	Be sure not to include any of the curl command statistics in the encrypted value. Outputting the value to a file can help avoid this problem.

The inverse operation is also available through /decrypt (provided the server is configured with a symmetric key or a full key pair), as shown in the following example:

$ curl localhost:8888/decrypt -d 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda
mysecret

	Tip
	If you testing with curl, then use --data-urlencode (instead of -d) or set an explicit Content-Type: text/plain to make sure curl encodes the data correctly when there are special characters ('+' is particularly tricky).

Take the encrypted value and add the {cipher} prefix before you put it in the YAML or properties file and before you commit and push it to a remote (potentially insecure) store.

The /encrypt and /decrypt endpoints also both accept paths in the form of /*/{name}/{profiles}, which can be used to control cryptography on a per-application (name) and per-profile basis when clients call into the main environment resource.

	Note
	To control the cryptography in this granular way, you must also provide a @Bean of type TextEncryptorLocator that creates a different encryptor per name and profiles. The one that is provided by default does not do so (all encryptions use the same key).

The spring command line client (with Spring Cloud CLI extensions installed) can also be used to encrypt and decrypt, as shown in the following example:

$ spring encrypt mysecret --key foo
682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda
$ spring decrypt --key foo 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda
mysecret

To use a key in a file (such as an RSA public key for encryption), prepend the key value with "@" and provide the file path, as shown in the following example:

$ spring encrypt mysecret --key @${HOME}/.ssh/id_rsa.pub
AQAjPgt3eFZQXwt8tsHAVv/QHiY5sI2dRcR+...

	Note
	The --key argument is mandatory (despite having a -- prefix).

The Config Server can use a symmetric (shared) key or an asymmetric one (RSA key pair). The asymmetric choice is superior in terms of security, but it is often more convenient to use a symmetric key since it is a single property value to configure in the bootstrap.properties.

To configure a symmetric key, you need to set encrypt.key to a secret String (or use the ENCRYPT_KEY environment variable to keep it out of plain-text configuration files).

	Note
	You cannot configure an asymmetric key using encrypt.key.

To configure an asymmetric key use a keystore (e.g. as created by the keytool utility that comes with the JDK). The keystore properties are encrypt.keyStore.* with * equal to

The encryption is done with the public key, and a private key is needed for decryption. Thus, in principle, you can configure only the public key in the server if you want to only encrypt (and are prepared to decrypt the values yourself locally with the private key). In practice, you might not want to do decrypt locally, because it spreads the key management process around all the clients, instead of concentrating it in the server. On the other hand, it can be a useful option if your config server is relatively insecure and only a handful of clients need the encrypted properties.

To create a keystore for testing, you can use a command resembling the following:

$ keytool -genkeypair -alias mytestkey -keyalg RSA \
  -dname "CN=Web Server,OU=Unit,O=Organization,L=City,S=State,C=US" \
  -keypass changeme -keystore server.jks -storepass letmein

Put the server.jks file in the classpath (for instance) and then, in your bootstrap.yml, for the Config Server, create the following settings:

encrypt:
  keyStore:
    location: classpath:/server.jks
    password: letmein
    alias: mytestkey
    secret: changeme

In addition to the {cipher} prefix in encrypted property values, the Config Server looks for zero or more {name:value} prefixes before the start of the (Base64 encoded) cipher text. The keys are passed to a TextEncryptorLocator, which can do whatever logic it needs to locate a TextEncryptor for the cipher. If you have configured a keystore (encrypt.keystore.location), the default locator looks for keys with aliases supplied by the key prefix, with a cipher text like resembling the following:

foo:
  bar: `{cipher}{key:testkey}...`

The locator looks for a key named "testkey". A secret can also be supplied by using a {secret:…​} value in the prefix. However, if it is not supplied, the default is to use the keystore password (which is what you get when you build a keystore and do not specify a secret). If you do supply a secret, you should also encrypt the secret using a custom SecretLocator.

When the keys are being used only to encrypt a few bytes of configuration data (that is, they are not being used elsewhere), key rotation is hardly ever necessary on cryptographic grounds. However, you might occasionally need to change the keys (for example, in the event of a security breach). In that case, all the clients would need to change their source config files (for example, in git) and use a new {key:…​} prefix in all the ciphers. Note that the clients need to first check that the key alias is available in the Config Server keystore.

	Tip
	If you want to let the Config Server handle all encryption as well as decryption, the {name:value} prefixes can also be added as plain text posted to the /encrypt endpoint, .

Sometimes you want the clients to decrypt the configuration locally, instead of doing it in the server. In that case, if you provide the encrypt.* configuration to locate a key, you can still have /encrypt and /decrypt endpoints, but you need to explicitly switch off the decryption of outgoing properties by placing spring.cloud.config.server.encrypt.enabled=false in bootstrap.[yml|properties]. If you do not care about the endpoints, it should work if you do not configure either the key or the enabled flag.

The default behavior for any application that has the Spring Cloud Config Client on the classpath is as follows: When a config client starts, it binds to the Config Server (through the spring.cloud.config.uri bootstrap configuration property) and initializes Spring Environment with remote property sources.

The net result of this behavior is that all client applications that want to consume the Config Server need a bootstrap.yml (or an environment variable) with the server address set in spring.cloud.config.uri (it defaults to "http://localhost:8888").

If you use a DiscoveryClient implementation, such as Spring Cloud Netflix and Eureka Service Discovery or Spring Cloud Consul, you can have the Config Server register with the Discovery Service. However, in the default “Config First” mode, clients cannot take advantage of the registration.

If you prefer to use DiscoveryClient to locate the Config Server, you can do so by setting spring.cloud.config.discovery.enabled=true (the default is false). The net result of doing so is that client applications all need a bootstrap.yml (or an environment variable) with the appropriate discovery configuration. For example, with Spring Cloud Netflix, you need to define the Eureka server address (for example, in eureka.client.serviceUrl.defaultZone). The price for using this option is an extra network round trip on startup, to locate the service registration. The benefit is that, as long as the Discovery Service is a fixed point, the Config Server can change its coordinates. The default service ID is configserver, but you can change that on the client by setting spring.cloud.config.discovery.serviceId (and on the server, in the usual way for a service, such as by setting spring.application.name).

The discovery client implementations all support some kind of metadata map (for example, we have eureka.instance.metadataMap for Eureka). Some additional properties of the Config Server may need to be configured in its service registration metadata so that clients can connect correctly. If the Config Server is secured with HTTP Basic, you can configure the credentials as user and password. Also, if the Config Server has a context path, you can set configPath. For example, the following YAML file is for a Config Server that is a Eureka client:

bootstrap.yml. 

eureka:
  instance:
    ...
    metadataMap:
      user: osufhalskjrtl
      password: lviuhlszvaorhvlo5847
      configPath: /config

In some cases, you may want to fail startup of a service if it cannot connect to the Config Server. If this is the desired behavior, set the bootstrap configuration property spring.cloud.config.fail-fast=true to make the client halt with an Exception.

If you expect that the config server may occasionally be unavailable when your application starts, you can make it keep trying after a failure. First, you need to set spring.cloud.config.fail-fast=true. Then you need to add spring-retry and spring-boot-starter-aop to your classpath. The default behavior is to retry six times with an initial backoff interval of 1000ms and an exponential multiplier of 1.1 for subsequent backoffs. You can configure these properties (and others) by setting the spring.cloud.config.retry.* configuration properties.

	Tip
	To take full control of the retry behavior, add a @Bean of type RetryOperationsInterceptor with an ID of configServerRetryInterceptor. Spring Retry has a RetryInterceptorBuilder that supports creating one.

The Config Service serves property sources from /{name}/{profile}/{label}, where the default bindings in the client app are as follows:

	Note
	When setting the property ${spring.application.name} do not prefix your app name with the reserved word application- to prevent issues resolving the correct property source.

You can override all of them by setting spring.cloud.config.* (where * is name, profile or label). The label is useful for rolling back to previous versions of configuration. With the default Config Server implementation, it can be a git label, branch name, or commit ID. Label can also be provided as a comma-separated list. In that case, the items in the list are tried one by one until one succeeds. This behavior can be useful when working on a feature branch. For instance, you might want to align the config label with your branch but make it optional (in that case, use spring.cloud.config.label=myfeature,develop).

To ensure high availability when you have multiple instances of Config Server deployed and expect one or more instances to be unavailable from time to time, you can either specify multiple URLs (as a comma-separated list under the spring.cloud.config.uri property) or have all your instances register in a Service Registry like Eureka ( if using Discovery-First Bootstrap mode ). Note that doing so ensures high availability only when the Config Server is not running (that is, when the application has exited) or when a connection timeout has occurred. For example, if the Config Server returns a 500 (Internal Server Error) response or the Config Client receives a 401 from the Config Server (due to bad credentials or other causes), the Config Client does not try to fetch properties from other URLs. An error of that kind indicates a user issue rather than an availability problem.

If you use HTTP basic security on your Config Server, it is currently possible to support per-Config Server auth credentials only if you embed the credentials in each URL you specify under the spring.cloud.config.uri property. If you use any other kind of security mechanism, you cannot (currently) support per-Config Server authentication and authorization.

If you want to configure read timeout, this can be done by using the property spring.cloud.config.request-read-timeout.

If you use HTTP Basic security on the server, clients need to know the password (and username if it is not the default). You can specify the username and password through the config server URI or via separate username and password properties, as shown in the following example:

bootstrap.yml. 

spring:
  cloud:
    config:
     uri: https://user:[email protected]

The following example shows an alternate way to pass the same information:

bootstrap.yml. 

spring:
  cloud:
    config:
     uri: https://myconfig.mycompany.com
     username: user
     password: secret

The spring.cloud.config.password and spring.cloud.config.username values override anything that is provided in the URI.

If you deploy your apps on Cloud Foundry, the best way to provide the password is through service credentials (such as in the URI, since it does not need to be in a config file). The following example works locally and for a user-provided service on Cloud Foundry named configserver:

bootstrap.yml. 

spring:
  cloud:
    config:
     uri: ${vcap.services.configserver.credentials.uri:http://user:password@localhost:8888}

If you use another form of security, you might need to provide a RestTemplate to the ConfigServicePropertySourceLocator (for example, by grabbing it in the bootstrap context and injecting it).

@Configuration
public class CustomConfigServiceBootstrapConfiguration {
    @Bean
    public ConfigServicePropertySourceLocator configServicePropertySourceLocator() {
        ConfigClientProperties clientProperties = configClientProperties();
       ConfigServicePropertySourceLocator configServicePropertySourceLocator =  new ConfigServicePropertySourceLocator(clientProperties);
        configServicePropertySourceLocator.setRestTemplate(customRestTemplate(clientProperties));
        return configServicePropertySourceLocator;
    }
}

org.springframework.cloud.bootstrap.BootstrapConfiguration = com.my.config.client.CustomConfigServiceBootstrapConfiguration

spring:
  cloud:
    config:
      token: YourVaultToken

Vault supports the ability to nest keys in a value stored in Vault, as shown in the following example:

echo -n '{"appA": {"secret": "appAsecret"}, "bar": "baz"}' | vault write secret/myapp -

This command writes a JSON object to your Vault. To access these values in Spring, you would use the traditional dot(.) annotation, as shown in the following example

@Value("${appA.secret}")
String name = "World";

The preceding code would sets the value of the name variable to appAsecret.

To include the Eureka Client in your project, use the starter with a group ID of org.springframework.cloud and an artifact ID of spring-cloud-starter-netflix-eureka-client. See the Spring Cloud Project page for details on setting up your build system with the current Spring Cloud Release Train.

When a client registers with Eureka, it provides meta-data about itself — such as host, port, health indicator URL, home page, and other details. Eureka receives heartbeat messages from each instance belonging to a service. If the heartbeat fails over a configurable timetable, the instance is normally removed from the registry.

The following example shows a minimal Eureka client application:

@SpringBootApplication
@RestController
public class Application {

    @RequestMapping("/")
    public String home() {
        return "Hello world";
    }

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }

}

Note that the preceding example shows a normal Spring Boot application. By having spring-cloud-starter-netflix-eureka-client on the classpath, your application automatically registers with the Eureka Server. Configuration is required to locate the Eureka server, as shown in the following example:

application.yml. 

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

In the preceding example, "defaultZone" is a magic string fallback value that provides the service URL for any client that does not express a preference (in other words, it is a useful default).

The default application name (that is, the service ID), virtual host, and non-secure port (taken from the Environment) are ${spring.application.name}, ${spring.application.name} and ${server.port}, respectively.

Having spring-cloud-starter-netflix-eureka-client on the classpath makes the app into both a Eureka “instance” (that is, it registers itself) and a “client” (it can query the registry to locate other services). The instance behaviour is driven by eureka.instance.* configuration keys, but the defaults are fine if you ensure that your application has a value for spring.application.name (this is the default for the Eureka service ID or VIP).

See EurekaInstanceConfigBean and EurekaClientConfigBean for more details on the configurable options.

To disable the Eureka Discovery Client, you can set eureka.client.enabled to false. Eureka Discovery Client will also be disabled when spring.cloud.discovery.enabled is set to false.

HTTP basic authentication is automatically added to your eureka client if one of the eureka.client.serviceUrl.defaultZone URLs has credentials embedded in it (curl style, as follows: http://user:password@localhost:8761/eureka). For more complex needs, you can create a @Bean of type DiscoveryClientOptionalArgs and inject ClientFilter instances into it, all of which is applied to the calls from the client to the server.

	Note
	Because of a limitation in Eureka, it is not possible to support per-server basic auth credentials, so only the first set that are found is used.

The status page and health indicators for a Eureka instance default to /info and /health respectively, which are the default locations of useful endpoints in a Spring Boot Actuator application. You need to change these, even for an Actuator application if you use a non-default context path or servlet path (such as server.servletPath=/custom). The following example shows the default values for the two settings:

application.yml. 

eureka:
  instance:
    statusPageUrlPath: ${server.servletPath}/info
    healthCheckUrlPath: ${server.servletPath}/health

These links show up in the metadata that is consumed by clients and are used in some scenarios to decide whether to send requests to your application, so it is helpful if they are accurate.

	Note
	In Dalston it was also required to set the status and health check URLs when changing that management context path. This requirement was removed beginning in Edgware.

If your app wants to be contacted over HTTPS, you can set two flags in the EurekaInstanceConfig:

Doing so makes Eureka publish instance information that shows an explicit preference for secure communication. The Spring Cloud DiscoveryClient always returns a URI starting with https for a service configured this way. Similarly, when a service is configured this way, the Eureka (native) instance information has a secure health check URL.

Because of the way Eureka works internally, it still publishes a non-secure URL for the status and home pages unless you also override those explicitly. You can use placeholders to configure the eureka instance URLs, as shown in the following example:

application.yml. 

eureka:
  instance:
    statusPageUrl: https://${eureka.hostname}/info
    healthCheckUrl: https://${eureka.hostname}/health
    homePageUrl: https://${eureka.hostname}/

(Note that ${eureka.hostname} is a native placeholder only available in later versions of Eureka. You could achieve the same thing with Spring placeholders as well — for example, by using ${eureka.instance.hostName}.)

Note

If your application runs behind a proxy, and the SSL termination is in the proxy (for example, if you run in Cloud Foundry or other platforms as a service), then you need to ensure that the proxy “forwarded” headers are intercepted and handled by the application. If the Tomcat container embedded in a Spring Boot application has explicit configuration for the 'X-Forwarded-\*` headers, this happens automatically. The links rendered by your app to itself being wrong (the wrong host, port, or protocol) is a sign that you got this configuration wrong.

By default, Eureka uses the client heartbeat to determine if a client is up. Unless specified otherwise, the Discovery Client does not propagate the current health check status of the application, per the Spring Boot Actuator. Consequently, after successful registration, Eureka always announces that the application is in 'UP' state. This behavior can be altered by enabling Eureka health checks, which results in propagating application status to Eureka. As a consequence, every other application does not send traffic to applications in states other then 'UP'. The following example shows how to enable health checks for the client:

application.yml. 

eureka:
  client:
    healthcheck:
      enabled: true

	Warning
	eureka.client.healthcheck.enabled=true should only be set in application.yml. Setting the value in bootstrap.yml causes undesirable side effects, such as registering in Eureka with an UNKNOWN status.

If you require more control over the health checks, consider implementing your own com.netflix.appinfo.HealthCheckHandler.

It is worth spending a bit of time understanding how the Eureka metadata works, so you can use it in a way that makes sense in your platform. There is standard metadata for information such as hostname, IP address, port numbers, the status page, and health check. These are published in the service registry and used by clients to contact the services in a straightforward way. Additional metadata can be added to the instance registration in the eureka.instance.metadataMap, and this metadata is accessible in the remote clients. In general, additional metadata does not change the behavior of the client, unless the client is made aware of the meaning of the metadata. There are a couple of special cases, described later in this document, where Spring Cloud already assigns meaning to the metadata map.

eureka:
  instance:
    hostname: ${vcap.application.uris[0]}
    nonSecurePort: 80

@Bean
@Profile("!default")
public EurekaInstanceConfigBean eurekaInstanceConfig(InetUtils inetUtils) {
  EurekaInstanceConfigBean b = new EurekaInstanceConfigBean(inetUtils);
  AmazonInfo info = AmazonInfo.Builder.newBuilder().autoBuild("eureka");
  b.setDataCenterInfo(info);
  return b;
}

eureka:
  instance:
    instanceId: ${spring.application.name}:${vcap.application.instance_id:${spring.application.instance_id:${random.value}}}

Once you have an application that is a discovery client, you can use it to discover service instances from the Eureka Server. One way to do so is to use the native com.netflix.discovery.EurekaClient (as opposed to the Spring Cloud DiscoveryClient), as shown in the following example:

@Autowired
private EurekaClient discoveryClient;

public String serviceUrl() {
    InstanceInfo instance = discoveryClient.getNextServerFromEureka("STORES", false);
    return instance.getHomePageUrl();
}

	Tip
	Do not use the EurekaClient in a @PostConstruct method or in a @Scheduled method (or anywhere where the ApplicationContext might not be started yet). It is initialized in a SmartLifecycle (with phase=0), so the earliest you can rely on it being available is in another SmartLifecycle with a higher phase.

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
    <exclusions>
        <exclusion>
            <groupId>com.sun.jersey</groupId>
            <artifactId>jersey-client</artifactId>
        </exclusion>
        <exclusion>
            <groupId>com.sun.jersey</groupId>
            <artifactId>jersey-core</artifactId>
        </exclusion>
        <exclusion>
            <groupId>com.sun.jersey.contribs</groupId>
            <artifactId>jersey-apache-client4</artifactId>
        </exclusion>
    </exclusions>
</dependency>

You need not use the raw Netflix EurekaClient. Also, it is usually more convenient to use it behind a wrapper of some sort. Spring Cloud has support for Feign (a REST client builder) and Spring RestTemplate through the logical Eureka service identifiers (VIPs) instead of physical URLs. To configure Ribbon with a fixed list of physical servers, you can set <client>.ribbon.listOfServers to a comma-separated list of physical addresses (or hostnames), where <client> is the ID of the client.

You can also use the org.springframework.cloud.client.discovery.DiscoveryClient, which provides a simple API (not specific to Netflix) for discovery clients, as shown in the following example:

@Autowired
private DiscoveryClient discoveryClient;

public String serviceUrl() {
    List<ServiceInstance> list = discoveryClient.getInstances("STORES");
    if (list != null && list.size() > 0 ) {
        return list.get(0).getUri();
    }
    return null;
}

Being an instance also involves a periodic heartbeat to the registry (through the client’s serviceUrl) with a default duration of 30 seconds. A service is not available for discovery by clients until the instance, the server, and the client all have the same metadata in their local cache (so it could take 3 heartbeats). You can change the period by setting eureka.instance.leaseRenewalIntervalInSeconds. Setting it to a value of less than 30 speeds up the process of getting clients connected to other services. In production, it is probably better to stick with the default, because of internal computations in the server that make assumptions about the lease renewal period.

If you have deployed Eureka clients to multiple zones, you may prefer that those clients use services within the same zone before trying services in another zone. To set that up, you need to configure your Eureka clients correctly.

First, you need to make sure you have Eureka servers deployed to each zone and that they are peers of each other. See the section on zones and regions for more information.

Next, you need to tell Eureka which zone your service is in. You can do so by using the metadataMap property. For example, if service 1 is deployed to both zone 1 and zone 2, you need to set the following Eureka properties in service 1:

Service 1 in Zone 1

eureka.instance.metadataMap.zone = zone1
eureka.client.preferSameZoneEureka = true

Service 1 in Zone 2

eureka.instance.metadataMap.zone = zone2
eureka.client.preferSameZoneEureka = true

To include Eureka Server in your project, use the starter with a group ID of org.springframework.cloud and an artifact ID of spring-cloud-starter-netflix-eureka-server. See the Spring Cloud Project page for details on setting up your build system with the current Spring Cloud Release Train.

	Note
	If your project already uses Thymeleaf as its template engine, the Freemarker templates of the Eureka server may not be loaded correctly. In this case it is necessary to configure the template loader manually:

application.yml. 

spring:
  freemarker:
    template-loader-path: classpath:/templates/
    prefer-file-system-access: false

The following example shows a minimal Eureka server:

@SpringBootApplication
@EnableEurekaServer
public class Application {

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }

}

The server has a home page with a UI and HTTP API endpoints for the normal Eureka functionality under /eureka/*.

The following links have some Eureka background reading: flux capacitor and google group discussion.

Tip

Due to Gradle’s dependency resolution rules and the lack of a parent bom feature, depending on spring-cloud-starter-netflix-eureka-server can cause failures on application startup. To remedy this issue, add the Spring Boot Gradle plugin and import the Spring cloud starter parent bom as follows: build.gradle.  buildscript { dependencies { classpath("org.springframework.boot:spring-boot-gradle-plugin:{spring-boot-docs-version}") } } apply plugin: "spring-boot" dependencyManagement { imports { mavenBom "org.springframework.cloud:spring-cloud-dependencies:{spring-cloud-version}" } }

The Eureka server does not have a back end store, but the service instances in the registry all have to send heartbeats to keep their registrations up to date (so this can be done in memory). Clients also have an in-memory cache of Eureka registrations (so they do not have to go to the registry for every request to a service).

By default, every Eureka server is also a Eureka client and requires (at least one) service URL to locate a peer. If you do not provide it, the service runs and works, but it fills your logs with a lot of noise about not being able to register with the peer.

See also below for details of Ribbon support on the client side for Zones and Regions.

The combination of the two caches (client and server) and the heartbeats make a standalone Eureka server fairly resilient to failure, as long as there is some sort of monitor or elastic runtime (such as Cloud Foundry) keeping it alive. In standalone mode, you might prefer to switch off the client side behavior so that it does not keep trying and failing to reach its peers. The following example shows how to switch off the client-side behavior:

application.yml (Standalone Eureka Server). 

server:
  port: 8761

eureka:
  instance:
    hostname: localhost
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

Notice that the serviceUrl is pointing to the same host as the local instance.

Eureka can be made even more resilient and available by running multiple instances and asking them to register with each other. In fact, this is the default behavior, so all you need to do to make it work is add a valid serviceUrl to a peer, as shown in the following example:

application.yml (Two Peer Aware Eureka Servers). 

---
spring:
  profiles: peer1
eureka:
  instance:
    hostname: peer1
  client:
    serviceUrl:
      defaultZone: http://peer2/eureka/

---
spring:
  profiles: peer2
eureka:
  instance:
    hostname: peer2
  client:
    serviceUrl:
      defaultZone: http://peer1/eureka/

In the preceding example, we have a YAML file that can be used to run the same server on two hosts (peer1 and peer2) by running it in different Spring profiles. You could use this configuration to test the peer awareness on a single host (there is not much value in doing that in production) by manipulating /etc/hosts to resolve the host names. In fact, the eureka.instance.hostname is not needed if you are running on a machine that knows its own hostname (by default, it is looked up by using java.net.InetAddress).

You can add multiple peers to a system, and, as long as they are all connected to each other by at least one edge, they synchronize the registrations amongst themselves. If the peers are physically separated (inside a data center or between multiple data centers), then the system can, in principle, survive “split-brain” type failures. You can add multiple peers to a system, and as long as they are all directly connected to each other, they will synchronize the registrations amongst themselves.

application.yml (Three Peer Aware Eureka Servers). 

eureka:
  client:
    serviceUrl:
      defaultZone: http://peer1/eureka/,http://peer2/eureka/,http://peer3/eureka/

---
spring:
  profiles: peer1
eureka:
  instance:
    hostname: peer1

---
spring:
  profiles: peer2
eureka:
  instance:
    hostname: peer2

---
spring:
  profiles: peer3
eureka:
  instance:
    hostname: peer3

In some cases, it is preferable for Eureka to advertise the IP addresses of services rather than the hostname. Set eureka.instance.preferIpAddress to true and, when the application registers with eureka, it uses its IP address rather than its hostname.

	Tip
	If the hostname cannot be determined by Java, then the IP address is sent to Eureka. Only explict way of setting the hostname is by setting eureka.instance.hostname property. You can set your hostname at the run-time by using an environment variable — for example, eureka.instance.hostname=${HOST_NAME}.

You can secure your Eureka server simply by adding Spring Security to your server’s classpath via spring-boot-starter-security. By default when Spring Security is on the classpath it will require that a valid CSRF token be sent with every request to the app. Eureka clients will not generally possess a valid cross site request forgery (CSRF) token you will need to disable this requirement for the /eureka/** endpoints. For example:

@EnableWebSecurity
class WebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.csrf().ignoringAntMatchers("/eureka/**");
        super.configure(http);
    }
}

For more information on CSRF see the Spring Security documentation.

A demo Eureka Server can be found in the Spring Cloud Samples repo.

The JAXB modules which the Eureka server depends upon were removed in JDK 11. If you intend to use JDK 11 when running a Eureka server you must include these dependencies in your POM or Gradle file.

<dependency>
	<groupId>org.glassfish.jaxb</groupId>
	<artifactId>jaxb-runtime</artifactId>
</dependency>

To include Hystrix in your project, use the starter with a group ID of org.springframework.cloud and a artifact ID of spring-cloud-starter-netflix-hystrix. See the Spring Cloud Project page for details on setting up your build system with the current Spring Cloud Release Train.

The following example shows a minimal Eureka server with a Hystrix circuit breaker:

@SpringBootApplication
@EnableCircuitBreaker
public class Application {

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }

}

@Component
public class StoreIntegration {

    @HystrixCommand(fallbackMethod = "defaultStores")
    public Object getStores(Map<String, Object> parameters) {
        //do stuff that might fail
    }

    public Object defaultStores(Map<String, Object> parameters) {
        return /* something useful */;
    }
}

The @HystrixCommand is provided by a Netflix contrib library called “javanica”. Spring Cloud automatically wraps Spring beans with that annotation in a proxy that is connected to the Hystrix circuit breaker. The circuit breaker calculates when to open and close the circuit and what to do in case of a failure.

To configure the @HystrixCommand you can use the commandProperties attribute with a list of @HystrixProperty annotations. See here for more details. See the Hystrix wiki for details on the properties available.

If you want some thread local context to propagate into a @HystrixCommand, the default declaration does not work, because it executes the command in a thread pool (in case of timeouts). You can switch Hystrix to use the same thread as the caller through configuration or directly in the annotation, by asking it to use a different “Isolation Strategy”. The following example demonstrates setting the thread in the annotation:

@HystrixCommand(fallbackMethod = "stubMyService",
    commandProperties = {
      @HystrixProperty(name="execution.isolation.strategy", value="SEMAPHORE")
    }
)
...

The same thing applies if you are using @SessionScope or @RequestScope. If you encounter a runtime exception that says it cannot find the scoped context, you need to use the same thread.

You also have the option to set the hystrix.shareSecurityContext property to true. Doing so auto-configures a Hystrix concurrency strategy plugin hook to transfer the SecurityContext from your main thread to the one used by the Hystrix command. Hystrix does not let multiple Hystrix concurrency strategy be registered so an extension mechanism is available by declaring your own HystrixConcurrencyStrategy as a Spring bean. Spring Cloud looks for your implementation within the Spring context and wrap it inside its own plugin.

The state of the connected circuit breakers are also exposed in the /health endpoint of the calling application, as shown in the following example:

{
    "hystrix": {
        "openCircuitBreakers": [
            "StoreIntegration::getStoresByLocationLink"
        ],
        "status": "CIRCUIT_OPEN"
    },
    "status": "UP"
}

To enable the Hystrix metrics stream, include a dependency on spring-boot-starter-actuator and set management.endpoints.web.exposure.include: hystrix.stream. Doing so exposes the /actuator/hystrix.stream as a management endpoint, as shown in the following example:

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-actuator</artifactId>
    </dependency>

To include the Hystrix Dashboard in your project, use the starter with a group ID of org.springframework.cloud and an artifact ID of spring-cloud-starter-netflix-hystrix-dashboard. See the Spring Cloud Project page for details on setting up your build system with the current Spring Cloud Release Train.

To run the Hystrix Dashboard, annotate your Spring Boot main class with @EnableHystrixDashboard. Then visit /hystrix and point the dashboard to an individual instance’s /hystrix.stream endpoint in a Hystrix client application.

	Note
	When connecting to a /hystrix.stream endpoint that uses HTTPS, the certificate used by the server must be trusted by the JVM. If the certificate is not trusted, you must import the certificate into the JVM in order for the Hystrix Dashboard to make a successful connection to the stream endpoint.

Looking at an individual instance’s Hystrix data is not very useful in terms of the overall health of the system. Turbine is an application that aggregates all of the relevant /hystrix.stream endpoints into a combined /turbine.stream for use in the Hystrix Dashboard. Individual instances are located through Eureka. Running Turbine requires annotating your main class with the @EnableTurbine annotation (for example, by using spring-cloud-starter-netflix-turbine to set up the classpath). All of the documented configuration properties from the Turbine 1 wiki apply. The only difference is that the turbine.instanceUrlSuffix does not need the port prepended, as this is handled automatically unless turbine.instanceInsertPort=false.

Note

By default, Turbine looks for the /hystrix.stream endpoint on a registered instance by looking up its hostName and port entries in Eureka and then appending /hystrix.stream to it. If the instance’s metadata contains management.port, it is used instead of the port value for the /hystrix.stream endpoint. By default, the metadata entry called management.port is equal to the management.port configuration property. It can be overridden though with following configuration:

eureka:
  instance:
    metadata-map:
      management.port: ${management.port:8081}

The turbine.appConfig configuration key is a list of Eureka serviceIds that turbine uses to lookup instances. The turbine stream is then used in the Hystrix dashboard with a URL similar to the following:

http://my.turbine.server:8080/turbine.stream?cluster=CLUSTERNAME

The cluster parameter can be omitted if the name is default. The cluster parameter must match an entry in turbine.aggregator.clusterConfig. Values returned from Eureka are upper-case. Consequently, the following example works if there is an application called customers registered with Eureka:

turbine:
  aggregator:
    clusterConfig: CUSTOMERS
  appConfig: customers

If you need to customize which cluster names should be used by Turbine (because you do not want to store cluster names in turbine.aggregator.clusterConfig configuration), provide a bean of type TurbineClustersProvider.

The clusterName can be customized by a SPEL expression in turbine.clusterNameExpression with root as an instance of InstanceInfo. The default value is appName, which means that the Eureka serviceId becomes the cluster key (that is, the InstanceInfo for customers has an appName of CUSTOMERS). A different example is turbine.clusterNameExpression=aSGName, which gets the cluster name from the AWS ASG name. The following listing shows another example:

turbine:
  aggregator:
    clusterConfig: SYSTEM,USER
  appConfig: customers,stores,ui,admin
  clusterNameExpression: metadata['cluster']

In the preceding example, the cluster name from four services is pulled from their metadata map and is expected to have values that include SYSTEM and USER.

To use the “default” cluster for all apps, you need a string literal expression (with single quotes and escaped with double quotes if it is in YAML as well):

turbine:
  appConfig: customers,stores
  clusterNameExpression: "'default'"

Spring Cloud provides a spring-cloud-starter-netflix-turbine that has all the dependencies you need to get a Turbine server running. To add Turbine, create a Spring Boot application and annotate it with @EnableTurbine.

	Note
	By default, Spring Cloud lets Turbine use the host and port to allow multiple processes per host, per cluster. If you want the native Netflix behavior built into Turbine to not allow multiple processes per host, per cluster (the key to the instance ID is the hostname), set turbine.combineHostPort=false.

[
  {
    "name": "RACES",
    "link": "http://localhost:8383/turbine.stream?cluster=RACES"
  },
  {
    "name": "WEB",
    "link": "http://localhost:8383/turbine.stream?cluster=WEB"
  }
]

In some environments (such as in a PaaS setting), the classic Turbine model of pulling metrics from all the distributed Hystrix commands does not work. In that case, you might want to have your Hystrix commands push metrics to Turbine. Spring Cloud enables that with messaging. To do so on the client, add a dependency to spring-cloud-netflix-hystrix-stream and the spring-cloud-starter-stream-* of your choice. See the Spring Cloud Stream documentation for details on the brokers and how to configure the client credentials. It should work out of the box for a local broker.

On the server side, create a Spring Boot application and annotate it with @EnableTurbineStream. The Turbine Stream server requires the use of Spring Webflux, therefore spring-boot-starter-webflux needs to be included in your project. By default spring-boot-starter-webflux is included when adding spring-cloud-starter-netflix-turbine-stream to your application.

You can then point the Hystrix Dashboard to the Turbine Stream Server instead of individual Hystrix streams. If Turbine Stream is running on port 8989 on myhost, then put http://myhost:8989 in the stream input field in the Hystrix Dashboard. Circuits are prefixed by their respective serviceId, followed by a dot (.), and then the circuit name.

Spring Cloud provides a spring-cloud-starter-netflix-turbine-stream that has all the dependencies you need to get a Turbine Stream server running. You can then add the Stream binder of your choice — such as spring-cloud-starter-stream-rabbit.

Turbine Stream server also supports the cluster parameter. Unlike Turbine server, Turbine Stream uses eureka serviceIds as cluster names and these are not configurable.

If Turbine Stream server is running on port 8989 on my.turbine.server and you have two eureka serviceIds customers and products in your environment, the following URLs will be available on your Turbine Stream server. default and empty cluster name will provide all metrics that Turbine Stream server receives.

http://my.turbine.sever:8989/turbine.stream?cluster=customers
http://my.turbine.sever:8989/turbine.stream?cluster=products
http://my.turbine.sever:8989/turbine.stream?cluster=default
http://my.turbine.sever:8989/turbine.stream

So, you can use eureka serviceIds as cluster names for your Turbine dashboard (or any compatible dashboard). You don’t need to configure any properties like turbine.appConfig, turbine.clusterNameExpression and turbine.aggregator.clusterConfig for your Turbine Stream server.

	Note
	Turbine Stream server gathers all metrics from the configured input channel with Spring Cloud Stream. It means that it doesn’t gather Hystrix metrics actively from each instance. It just can provide metrics that were already gathered into the input channel by each instance.