This project provides Consul integrations for Spring Boot apps through autoconfiguration and binding to the Spring Environment and other Spring programming model idioms. With a few simple annotations you can quickly enable and configure the common patterns inside your application and build large distributed systems with Consul based components. The patterns provided include Service Discovery, Control Bus and Configuration. Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Breaker (Hystrix) are provided by integration with Spring Cloud Netflix.
Install Consul
Please see the installation documentation for instructions on how to install Consul.
Consul Agent
A Consul Agent client must be available to all Spring Cloud Consul applications. By default, the Agent client is expected to be at localhost:8500
. See the Agent documentation for specifics on how to start an Agent client and how to connect to a cluster of Consul Agent Servers. For development, after you have installed consul, you may start a Consul Agent using the following command:
./src/main/bash/local_run_consul.sh
This will start an agent in server mode on port 8500, with the ui available at http://localhost:8500
Service Discovery with Consul
Service Discovery is one of the key tenets of a microservice based architecture. Trying to hand configure each client or some form of convention can be very difficult to do and can be very brittle. Consul provides Service Discovery services via an HTTP API and DNS. Spring Cloud Consul leverages the HTTP API for service registration and discovery. This does not prevent non-Spring Cloud applications from leveraging the DNS interface. Consul Agents servers are run in a cluster that communicates via a gossip protocol and uses the Raft consensus protocol.
Registering with Consul
When a client registers with Consul, it provides meta-data about itself such as host and port, id, name and tags. An HTTP Check is created by default that Consul hits the /health
endpoint every 10 seconds. If the health check fails, the service instance is marked as critical.
Example Consul client:
@SpringBootApplication
@EnableDiscoveryClient
@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);
}
}
(i.e. utterly normal Spring Boot app). If the Consul client is located somewhere other than localhost:8500
, the configuration is required to locate the client. Example:
spring: cloud: consul: host: localhost port: 8500
Caution
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If you use Spring Cloud Consul Config, the above values will need to be placed in bootstrap.yml instead of application.yml .
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The default service name, instance id and port, taken from the Environment
, are ${spring.application.name}
, the Spring Context ID and ${server.port}
respectively.
@EnableDiscoveryClient
make the app into both a Consul "service" (i.e. it registers itself) and a "client" (i.e. it can query Consul to locate other services).
HTTP Health Check
The health check for a Consul instance defaults to "/health", which is the default locations of a useful endpoint 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 (e.g. server.servletPath=/foo
) or management endpoint path (e.g. management.contextPath=/admin
). The interval that Consul uses to check the health endpoint may also be configured. "10s" and "1m" represent 10 seconds and 1 minute respectively. Example:
spring: cloud: consul: discovery: healthCheckPath: ${management.contextPath}/health healthCheckInterval: 15s
Metadata and Consul tags
Consul does not yet support metadata on services. Spring Cloud’s ServiceInstance
has a Map<String, String> metadata
field. Spring Cloud Consul uses Consul tags to approximate metadata until Consul officially supports metadata. Tags with the form key=value
will be split and used as a Map
key and value respectively. Tags without the equal =
sign, will be used as both the key and value.
spring: cloud: consul: discovery: tags: foo=bar, baz
The above configuration will result in a map with foo→bar
and baz→baz
.
Making the Consul Instance ID Unique
By default a consul instance is registered with an ID that is equal to its Spring Application Context ID. By default, the Spring Application Context ID is ${spring.application.name}:comma,separated,profiles:${server.port}
. For most cases, this will allow multiple instances of one service to run on one machine. If further uniqueness is required, Using Spring Cloud you can override this by providing a unique identifier in spring.cloud.consul.discovery.instanceId
. For example:
spring: cloud: consul: discovery: instanceId: ${spring.application.name}:${spring.application.instance_id:${random.value}}
With this metadata, and multiple service instances deployed on localhost, the random value will kick in there to make the instance unique. In Cloudfoundry the spring.application.instance_id
will be populated automatically in a Spring Boot Actuator application, so the random value will not be needed.
Using the DiscoveryClient
Spring Cloud has support for Feign (a REST client builder) and also Spring RestTemplate
using the logical service names instead of physical URLs.
You can also use the org.springframework.cloud.client.discovery.DiscoveryClient
which provides a simple API for discovery clients that is not specific to Netflix, e.g.
@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; }
Distributed Configuration with Consul
Consul provides a Key/Value Store for storing configuration and other metadata. Spring Cloud Consul Config is an alternative to the Config Server and Client. Configuration is loaded into the Spring Environment during the special "bootstrap" phase. Configuration is stored in the /config
folder by default. Multiple PropertySource
instances are created based on the application’s name and the active profiles that mimicks the Spring Cloud Config order of resolving properties. For example, an application with the name "testApp" and with the "dev" profile will have the following property sources created:
config/testApp,dev/ config/testApp/ config/application,dev/ config/application/
The most specific property source is at the top, with the least specific at the bottom. Properties is the config/application
folder are applicable to all applications using consul for configuration. Properties in the config/testApp
folder are only available to the instances of the service named "testApp".
Configuration is currently read on startup of the application. Sending a HTTP POST to /refresh
will cause the configuration to be reloaded. Watching the key value store (which Consul supports) is not currently possible, but will be a future addition to this project.
How to activate
Including a dependency on org.springframework.cloud:spring-cloud-consul-config
will enable auto-configuration that will setup Spring Cloud Consul Config.
Customizing
Consul Config may be customized using the following properties:
spring: cloud: consul: config: enabled: true prefix: configuration defaultContext: apps profileSeparator: '::'
-
enabled
setting this value to "false" disables Consul Config -
prefix
sets the base folder for configuration values -
defaultContext
sets the folder name used by all applications -
profileSeparator
sets the value of the separator used to separate the profile name in property sources with profiles
YAML or Properties with Config
It may be more convenient to store a blob of properties in YAML or Properties format as opposed to individual key/value pairs. Set the spring.cloud.consul.config.format
property to YAML
or PROPERTIES
. For example to use YAML:
spring: cloud: consul: config: format: YAML
YAML must be set in the appropriate data
key in consul. Using the defaults above the keys would look like:
config/testApp,dev/data config/testApp/data config/application,dev/data config/application/data
You could store a YAML document in any of the keys listed above.
You can change the data key using spring.cloud.consul.config.data-key
.
git2consul with Config
git2consul is a Consul community project that loads files from a git repository to individual keys into Consul. By default the names of the keys are names of the files. YAML and Properties files are supported with file extensions of .yml
and .properties
respectively. Set the spring.cloud.consul.config.format
property to FILES
. For example:
spring: cloud: consul: config: format: FILES
Given the following keys in /config
, the development
profile and an application name of foo
:
.gitignore application.yml bar.properties foo-development.properties foo-production.yml foo.properties master.ref
the following property sources would be created:
config/foo-development.properties config/foo.properties config/application.yml
The value of each key needs to be a properly formatted YAML or Properties file.
Fail Fast
It may be convenient in certain circumstances (like local development or certain test scenarios) to not fail if consul isn’t available for configuration. Setting spring.cloud.consul.config.failFast=false
in bootstrap.yml
will cause the configuration module to log a warning rather than throw an exception. This will allow the application to continue startup normally.
Consul Retry
If you expect that the consul agent may occasionally be unavailable when
your app starts, you can ask it to keep trying after a failure. You need to add
spring-retry
and spring-boot-starter-aop
to your classpath. The default
behaviour is to retry 6 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) using spring.cloud.consul.retry.*
configuration properties.
This works with both Spring Cloud Consul Config and Discovery registration.
Tip
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To take full control of the retry add a @Bean of type
RetryOperationsInterceptor with id "consulRetryInterceptor". Spring
Retry has a RetryInterceptorBuilder that makes it easy to create one.
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Spring Cloud Bus with Consul
Coming in a later release.
Circuit Breaker with Hystrix
Applications can use the Hystrix Circuit Breaker provided by the Spring Cloud Netflix project by including this starter in the projects pom.xml: spring-cloud-starter-hystrix
. Hystrix doesn’t depend on the Netflix Discovery Client. The @EnableHystrix
annotation should be placed on a configuration class (usually the main class). Then methods can be annotated with @HystrixCommand
to be protected by a circuit breaker. See the documentation for more details.
Hystrix metrics aggregation with Turbine and Consul
Turbine (provided by the Spring Cloud Netflix project), aggregates multiple instances Hystrix metrics streams, so the dashboard can display an aggregate view. Turbine uses the DiscoveryClient
interface to lookup relevant instances. To use Turbine with Spring Cloud Consul, configure the Turbine application in a manner similar to the following examples:
<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-netflix-turbine</artifactId> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-consul-discovery</artifactId> </dependency>
Notice that the Turbine dependency is not a starter. The turbine starter includes support for Netflix Eureka.
spring.application.name: turbine applications: consulhystrixclient turbine: aggregator: clusterConfig: ${applications} appConfig: ${applications}
The clusterConfig
and appConfig
sections must match, so it’s useful to put the comma-separated list of service ID’s into a separate configuration property.
@EnableTurbine @EnableDiscoveryClient @SpringBootApplication public class Turbine { public static void main(String[] args) { SpringApplication.run(DemoturbinecommonsApplication.class, args); } }