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Spring Cloud Netflix: Client Side Load Balancing

Estimated Time: 25 minutes

Requirements

Lab Requirements

What You Will Learn

  • How to use Ribbon as a client side load balancer
  • How to use a Ribbon enabled RestTemplate

Exercises

Start the config-server, service-registry, and fortune-service

  1. Start the config-server in a terminal window. You may have terminal windows still open from previous labs. They may be reused for this lab.
$ cd $SPRING_CLOUD_SERVICES_LABS_HOME/config-server
$ mvn clean spring-boot:run
  1. Start the service-registry
$ cd $SPRING_CLOUD_SERVICES_LABS_HOME/service-registry
$ mvn clean spring-boot:run
  1. Start the fortune-service
$ cd $SPRING_CLOUD_SERVICES_LABS_HOME/fortune-service
$ mvn clean spring-boot:run

Set up greeting-ribbon

No additions to the pom.xml

In this case, we don't need to explicitly include Ribbon support in the pom.xml. Ribbon support is pulled in through transitive dependencies (dependencies of the dependencies we have already defined).

  1. Review the the following file: $SPRING_CLOUD_SERVICES_LABS_HOME/greeting-ribbon/src/main/java/io/pivotal/greeting/GreetingController.java. Notice the loadBalancerClient. It is a client side load balancer (Ribbon). Review the fetchFortuneServiceUrl() method. Ribbon is integrated with Eureka so that it can discover services as well. Notice how the loadBalancerClient chooses a service instance by name.
@Controller
public class GreetingController {

	Logger logger = LoggerFactory
			.getLogger(GreetingController.class);




	@Autowired
	private LoadBalancerClient loadBalancerClient;

	@RequestMapping("/")
	String getGreeting(Model model){

		logger.debug("Adding greeting");
		model.addAttribute("msg", "Greetings!!!");


		RestTemplate restTemplate = new RestTemplate();
        String fortune = restTemplate.getForObject(fetchFortuneServiceUrl(), String.class);

		logger.debug("Adding fortune");
		model.addAttribute("fortune", fortune);

		//resolves to the greeting.vm velocity template
		return "greeting";
	}

	private String fetchFortuneServiceUrl() {
	    ServiceInstance instance = loadBalancerClient.choose("fortune-service");

	    logger.debug("uri: {}",instance.getUri().toString());
	    logger.debug("serviceId: {}", instance.getServiceId());


	    return instance.getUri().toString();
	}

}
  1. Open a new terminal window. Start the greeting-ribbon app.
$ cd $SPRING_CLOUD_SERVICES_LABS_HOME/greeting-ribbon
$ mvn clean spring-boot:run

  1. After the a few moments, check the service-registry dashboard. Confirm the greeting-ribbon app is registered.

  2. Browse to the greeting-ribbon application. Confirm you are seeing fortunes. Refresh as desired. Also review the terminal output for the greeting-ribbon app. See the uri and serviceId being logged.

  3. Stop the greeting-ribbon application.

Set up greeting-ribbon-rest

No additions to the pom.xml

In this case, we don't need to explicitly include Ribbon support in the pom.xml. Ribbon support is pulled in through transitive dependencies (dependencies of the dependencies we have already defined).

  1. Review the the following file: $SPRING_CLOUD_SERVICES_LABS_HOME/greeting-ribbon-rest/src/main/java/io/pivotal/greeting/GreetingController.java. Notice the RestTemplate. It is not the usual RestTemplate, it is load balanced by Ribbon. The @LoadBalanced annotation is a qualifier to ensure we get the load balanced RestTemplate injected. This further simplifies application code.
@Controller
public class GreetingController {

	Logger logger = LoggerFactory
			.getLogger(GreetingController.class);




	@Autowired
	@LoadBalanced
	private RestTemplate restTemplate;

	@RequestMapping("/")
	String getGreeting(Model model){

		logger.debug("Adding greeting");
		model.addAttribute("msg", "Greetings!!!");


  	String fortune = restTemplate.getForObject("http://fortune-service", String.class);

		logger.debug("Adding fortune");
		model.addAttribute("fortune", fortune);

		//resolves to the greeting.vm velocity template
		return "greeting";
	}


}
  1. Open a new terminal window. Start the greeting-ribbon-rest app.
$ cd $SPRING_CLOUD_SERVICES_LABS_HOME/greeting-ribbon-rest
$ mvn clean spring-boot:run

  1. After the a few moments, check the service-registry dashboard. Confirm the greeting-ribbon-rest app is registered.

  2. Browse to the greeting-ribbon-rest application. Confirm you are seeing fortunes. Refresh as desired. Also review the terminal output for the greeting-ribbon-rest app.

  3. When done stop the config-server, service-registry, fortune-service and greeting-ribbon-rest applications.

Deploy the greeting-ribbon-rest to PCF

  1. Package and push the greeting-ribbon-rest application.
$ mvn clean package
$ cf push greeting-ribbon-rest -p target/greeting-ribbon-rest-0.0.1-SNAPSHOT.jar -m 512M --random-route --no-start
  1. Bind services for the greeting-ribbon-rest application.
$ cf bind-service greeting-ribbon-rest config-server
$ cf bind-service greeting-ribbon-rest service-registry

You can safely ignore the TIP: Use 'cf restage' to ensure your env variable changes take effect message from the CLI. We don't need to restage at this time.

  1. If using self signed certificates, set the CF_TARGET environment variable for the greeting-ribbon-rest application.
$ cf set-env greeting-ribbon-rest CF_TARGET <your api endpoint - make sure it starts with "https://">

You can safely ignore the TIP: Use 'cf restage' to ensure your env variable changes take effect message from the CLI. We don't need to restage at this time.

  1. Start the greeting-ribbon-rest app.
$ cf start greeting-ribbon-rest

  1. After the a few moments, check the service-registry. Confirm the greeting-ribbon-rest app is registered.

  2. Refresh the greeting-ribbon-rest / endpoint.

Note About This Lab

If services (e.g. fortune-service) are registering using the first Cloud Foundry URI (using the route registration method) this means that requests to them are being routed through the router and subsequently load balanced at that layer. Therefore, client side load balancing doesn't occur.

Pivotal Cloud Foundry has recently added support for allowing cross container communication. This will allow applications to communicate with each other without passing through the router. As applied to client-side load balancing, services such as fortune-service would register with Eureka using their container IP addresses. Allowing clients to reach them without going through the router. This is known as using the direct registration method.

For more details, please read the following.