Ribbon负载均衡分析

负载均衡原理分析

@LoadBalanced
@Bean
public RestTemplate restTemplate(RestTemplateBuilder builder) {
     
    return builder
        .setConnectTimeout(Duration.ofMillis(100))
        .setReadTimeout(Duration.ofMillis(500))
        .requestFactory(this::requestFactory)
        .build();
}

进入该注解@LoadBalanced以看到

Annotation to mark a RestTemplate bean to be configured to use a LoadBalancerClient.

打开LoadBalancerClient 的实现类**RibbonLoadBalancerClient**

//使用LoadBalancer的ServiceInstance对指定的服务执行请求。
 T execute(String serviceId, ServiceInstance serviceInstance,
			LoadBalancerRequest request) throws IOException;

//RibbonLoadBalancerClient的实现
public <T> T execute(String serviceId, LoadBalancerRequest<T> request, Object hint)
			throws IOException {
     
		ILoadBalancer loadBalancer = getLoadBalancer(serviceId);
		Server server = getServer(loadBalancer, hint);
		if (server == null) {
     
			throw new IllegalStateException("No instances available for " + serviceId);
		}
		RibbonServer ribbonServer = new RibbonServer(serviceId, server,
				isSecure(server, serviceId),
				serverIntrospector(serviceId).getMetadata(server));

		return execute(serviceId, ribbonServer, request);
	}

Server server = getServer(loadBalancer, hint); 进入

protected Server getServer(ILoadBalancer loadBalancer, Object hint) {
     
		if (loadBalancer == null) {
     
			return null;
		}
		// Use 'default' on a null hint, or just pass it on?
		return loadBalancer.chooseServer(hint != null ? hint : "default");
	}

可以看到loadBalancer.chooseServer 选择服务器

com.netflix.loadbalancer.BaseLoadBalancer#chooseServer

public Server chooseServer(Object key) {
     
        if (counter == null) {
     
            counter = createCounter();
        }
        counter.increment();
        if (rule == null) {
     
            return null;
        } else {
     
            try {
     
                // 通过rule 执行负载均衡策略。 默认轮训
                return rule.choose(key);
            } catch (Exception e) {
     
                logger.warn("LoadBalancer [{}]:  Error choosing server for key {}", name, key, e);
                return null;
            }
        }
    }

默认是使用IRule DEFAULT_RULE = new RoundRobinRule();

Ribbon更改负载均衡模式

• .新建一个更改负载均衡的类，这个类不能放在能被@componentScan扫描的包下

@Configuration
public class BalanceRule {
     
    @Bean
    RandomRule randomRule(){
     
        return new RandomRule(); #内置的负载均衡规则
    }
}

然后启动类中加上@RibbonClient(name = “payment”,configuration = BalanceRule.class)

常用负载均衡算法

• RoundRobinRule 轮询
• RandomRule 随机
• AvailabilityFilteringRule 会先过滤掉由于多次访问故障而处于断路器跳闸状态的服务，还有并发的连接数超过阈值的服务，然后对剩余的服务列表进行轮询
• WeightedResponseTimeRule 权重 根据平均响应时间计算所有服务的权重，响应时间越快服务权重越大被选中的概率越高。刚启动时，如果统计信息不足，则使用轮询策略，等信息足够，切换到 WeightedResponseTimeRule
• RetryRule 重试 先按照轮询策略获取服务，如果获取失败则在指定时间内重试，获取可用服务
• BestAvailableRule 选过滤掉多次访问故障而处于断路器跳闸状态的服务，然后选择一个并发量最小的服务
• ZoneAvoidanceRule 符合判断server所在区域的性能和server的可用性选择服务