19. Polyglot support with Sidecar

Do you have non-JVM languages with which you want to take advantage of Eureka, Ribbon, and Config Server? The Spring Cloud Netflix Sidecar was inspired by Netflix Prana. It includes an HTTP API to get all of the instances (by host and port) for a given service. You can also proxy service calls through an embedded Zuul proxy that gets its route entries from Eureka. The Spring Cloud Config Server can be accessed directly through host lookup or through the Zuul Proxy. The non-JVM application should implement a health check so the Sidecar can report to Eureka whether the app is up or down.

To include Sidecar in your project, use the dependency with a group ID of org.springframework.cloud and artifact ID or spring-cloud-netflix-sidecar.

To enable the Sidecar, create a Spring Boot application with @EnableSidecar. This annotation includes @EnableCircuitBreaker, @EnableDiscoveryClient, and @EnableZuulProxy. Run the resulting application on the same host as the non-JVM application.

To configure the side car, add sidecar.port and sidecar.health-uri to application.yml. The sidecar.port property is the port on which the non-JVM application listens. This is so the Sidecar can properly register the application with Eureka. The sidecar.health-uri is a URI accessible on the non-JVM application that mimics a Spring Boot health indicator. It should return a JSON document that resembles the following:

health-uri-document. 

{
  "status":"UP"
}

HThe following application.yml example shows sample configuration for a Sidecar application:

application.yml. 

server:
  port: 5678
spring:
  application:
    name: sidecar

sidecar:
  port: 8000
  health-uri: http://localhost:8000/health.json

The API for the DiscoveryClient.getInstances() method is /hosts/{serviceId}. The following example response for /hosts/customers returns two instances on different hosts:

/hosts/customers. 

[
    {
        "host": "myhost",
        "port": 9000,
        "uri": "http://myhost:9000",
        "serviceId": "CUSTOMERS",
        "secure": false
    },
    {
        "host": "myhost2",
        "port": 9000,
        "uri": "http://myhost2:9000",
        "serviceId": "CUSTOMERS",
        "secure": false
    }
]

This API is accessible to the non-JVM application (if the sidecar is on port 5678) at http://localhost:5678/hosts/{serviceId}.

The Zuul proxy automatically adds routes for each service known in Eureka to /<serviceId>, so the customers service is available at /customers. The non-JVM application can access the customer service at http://localhost:5678/customers (assuming the sidecar is listening on port 5678).

If the Config Server is registered with Eureka, the non-JVM application can access it through the Zuul proxy. If the serviceId of the ConfigServer is configserver and the Sidecar is on port 5678, then it can be accessed at http://localhost:5678/configserver.

Non-JVM applications can take advantage of the Config Server’s ability to return YAML documents. For example, a call to http://sidecar.local.spring.io:5678/configserver/default-master.yml might result in a YAML document resembling the following:

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  password: password
info:
  description: Spring Cloud Samples
  url: https://github.com/spring-cloud-samples