Consul and Spring Boot

Introduction#

The Consul integration in Spring Boot is comparable to the integration of Eureka (see Eureka: Service Discovery).

There is a configuration file application.properties. Here is the relevant section:

spring.application.name=catalog
spring.cloud.consul.host=consul
spring.cloud.consul.port=8500
spring.cloud.consul.discovery.preferIpAddress=true
spring.cloud.consul.discovery.instanceId=\＄{spring.application.name}:
\＄{spring.application.instance_id:\＄{random.value}}

The section configures the following values:

• spring.application.name defines the name under which the application is registered in Consul.

• spring.cloud.consul.host and spring.cloud.consul.port determine at which port and on which host Consul can be accessed.

• Via spring.cloud.consul.discovery.preferIpAddress the services register with their IP address and not with the host name. This circumvents problems that arise because host names cannot be resolved in the Docker environment.

• spring.cloud.consul.discovery.instanceId assigns an unambiguous ID to each microservice instance for discriminating between instances for load balancing.

Code dependencies#

In addition, a dependency to spring-cloud-starter-consul-discovery has to be inserted in pom.xml for the build. Moreover, the main class of the application that has the annotation @SpringBootApplication has to be annotated with @EnableDiscoveryClient.

Health check with Spring Boot Actuator#

Finally, the microservice must provide a health check. Spring Boot contains the Actuator module for this, which offers a health check as well as metrics. The health check is available at the URL /health. This is exactly the URL Consul requests. It is enough to add a dependency to spring-boot-starter-actuator in the pom.xml. Specific health checks may need to be developed if the application depends on additional resources.

Consul and Ribbon#

Of course, a microservice must also use Consul to communicate with other microservices. For this, the Consul example uses the Ribbon library analogous to the Netflix example (see Load Balancing: Ribbon).

Ribbon has been modified in the Spring Cloud project so that it can also deal with Consul. Because the microservices use Ribbon, the rest of the code is unchanged compared to the Netflix example.

                                                 Q U I Z  

In the next lesson, we’ll discuss DNS and registrator.