ribbon is responsible for load balancing of services.

Spring cloud has two kinds of service invocation methods, one is ribbon+restTemplate, the other is feign.

ribbon is simple to use as follows:

1. Introducing Dependence

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
</dependency>

2. Insert a RestTemplate into spring boot and add the @LoadBalanced annotation

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate(){
        return new RestTemplate();
    }

3. Call mode

Inject a RestTemplate where the service needs to be invoked. Write the service ID at the url, and ribbon will help us resolve it into IP and port addresses.

    @RequestMapping("{userId}")
    public String getAll2(@PathVariable("userId") String id) {
        String url = "http://search-service/"+id;
        System.out.println(url);
        return restTemplate.getForObject(url, String.class);;
    }

4. The @LoadBalanced annotation automatically implements load balancing and service IP port parsing source tracking as follows:

The reason ribbon can achieve these functions mainly depends on LoadBalancer's interceptor. View the LoadBalancerInterceptor class

public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {

	private LoadBalancerClient loadBalancer;
	private LoadBalancerRequestFactory requestFactory;

	public LoadBalancerInterceptor(LoadBalancerClient loadBalancer, LoadBalancerRequestFactory requestFactory) {
		this.loadBalancer = loadBalancer;
		this.requestFactory = requestFactory;
	}

	public LoadBalancerInterceptor(LoadBalancerClient loadBalancer) {
		// for backwards compatibility
		this(loadBalancer, new LoadBalancerRequestFactory(loadBalancer));
	}

	@Override
	public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
			final ClientHttpRequestExecution execution) throws IOException {
		final URI originalUri = request.getURI();
		String serviceName = originalUri.getHost();
		Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);
		return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));
	}
}

Enter the execute method, at originalUri.getHost(); then load balancing will select the corresponding service and port IP. The default ribbon load balancing strategy is

IRule DEFAULT_RULE = new Round Robin Rule (); is a linear load balancing strategy, a polling method, through the calculation of counters and models to select services.

Of course, you can change to other strategies.

Configure in the configuration file

service-name: #Service name
  ribbon:
    NFLoadBalancerRuleClassName: com.netflix.loadbalancer.RandomRule #Change to a random strategy