10. Spring Cloud Config Client

A Spring Boot application can take immediate advantage of the Spring Config Server (or other external property sources provided by the application developer). It also picks up some additional useful features related to Environment change events.

10.1 Config First Bootstrap

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 applciations 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").

10.2 Discovery First Bootstrap

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 username 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

10.3 Config Client Fail Fast

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.

10.4 Config Client Retry

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]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.

10.5 Locating Remote Configuration Resources

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

  • "name" = ${spring.application.name}
  • "profile" = ${spring.profiles.active} (actually Environment.getActiveProfiles())
  • "label" = "master"

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).

10.6 Specifying Multiple Urls for the Config Server

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.

10.7 Configuring Read Timeouts

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

10.8 Security

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:[email protected]: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).

10.8.1 Health Indicator

The Config Client supplies a Spring Boot Health Indicator that attempts to load configuration from the Config Server. The health indicator can be disabled by setting health.config.enabled=false. The response is also cached for performance reasons. The default cache time to live is 5 minutes. To change that value, set the health.config.time-to-live property (in milliseconds).

10.8.2 Providing A Custom RestTemplate

In some cases, you might need to customize the requests made to the config server from the client. Typically, doing so involves passing special Authorization headers to authenticate requests to the server. To provide a custom RestTemplate:

  1. Create a new configuration bean with an implementation of PropertySourceLocator, as shown in the following example:

CustomConfigServiceBootstrapConfiguration.java. 

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

  1. In resources/META-INF, create a file called spring.factories and specify your custom configuration, as shown in the following example:

spring.factories. 

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

10.8.3 Vault

When using Vault as a backend to your config server, the client needs to supply a token for the server to retrieve values from Vault. This token can be provided within the client by setting spring.cloud.config.token in bootstrap.yml, as shown in the following example:

bootstrap.yml. 

spring:
  cloud:
    config:
      token: YourVaultToken

10.9 Nested Keys In Vault

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.