nacos或者eureka采用ribbon作为负载均衡导致服务下线感知30s

1.nacos、eureka上线下线

最近在进行eureka切换为nacos作为服务发现中间件。在采用金丝雀灰度发布的过程中发现服务已经把原的Eureka中注册的服务进行下线操作了，但是仍然有流量请求进来，这样就违背了官方宣称的秒级上下线特点。其中我们服务的负载均衡使用的ribbon这个负载均衡组件。以nacos为例子：

public String update(HttpServletRequest request) throws Exception {
	String serviceName = WebUtils.required(request, CommonParams.SERVICE_NAME);
	String namespaceId = WebUtils.optional(request, CommonParams.NAMESPACE_ID, Constants.DEFAULT_NAMESPACE_ID);

	String agent = request.getHeader("Client-Version");
	if (StringUtils.isBlank(agent)) {
		agent = request.getHeader("User-Agent");
	}

	ClientInfo clientInfo = new ClientInfo(agent);

	if (clientInfo.type == ClientInfo.ClientType.JAVA &&
		clientInfo.version.compareTo(VersionUtil.parseVersion("1.0.0")) >= 0) {
		serviceManager.updateInstance(namespaceId, serviceName, parseInstance(request));
	} else {
		serviceManager.registerInstance(namespaceId, serviceName, parseInstance(request));
	}
	return "ok";
}

上边这段代码说明的是nacos进行上线下线的逻辑，可以看到核心逻辑是parseInstance()方法，里面的的实例信息就是从request中获取的。再看一下updateInstance方法：

public void updateInstance(String namespaceId, String serviceName, Instance instance) throws NacosException {

	Service service = getService(namespaceId, serviceName);

	if (service == null) {
		throw new NacosException(NacosException.INVALID_PARAM, "service not found, namespace: " + namespaceId + ", service: " + serviceName);
	}

	if (!service.allIPs().contains(instance)) {
		throw new NacosException(NacosException.INVALID_PARAM, "instance not exist: " + instance);
	}

	addInstance(namespaceId, serviceName, instance.isEphemeral(), instance);
}

public void addInstance(String namespaceId, String serviceName, boolean ephemeral, Instance... ips) throws NacosException {

	String key = KeyBuilder.buildInstanceListKey(namespaceId, serviceName, ephemeral);

	Service service = getService(namespaceId, serviceName);

	List<Instance> instanceList = addIpAddresses(service, ephemeral, ips);

	Instances instances = new Instances();
	instances.setInstanceList(instanceList);

	consistencyService.put(key, instances);
}

可以看到实例下线，是立马更新server中的实例信息数据的。

2.Ribbon负载均衡更新机制

NacosServerList继承了AbstractServerList最终是在DynamicServerListLoadBalancer这类中进行负载所有的server的

public class NacosServerList extends AbstractServerList<NacosServer> {

	private NacosDiscoveryProperties discoveryProperties;

	private String serviceId;

	public NacosServerList(NacosDiscoveryProperties discoveryProperties) {
		this.discoveryProperties = discoveryProperties;
	}

	@Override
	public List<NacosServer> getInitialListOfServers() {
		return getServers();
	}

	@Override
	public List<NacosServer> getUpdatedListOfServers() {
		return getServers();
	}

	private List<NacosServer> getServers() {
		try {
			List<Instance> instances = discoveryProperties.namingServiceInstance()
					.selectInstances(serviceId, true);
			return instancesToServerList(instances);
		}
		catch (Exception e) {
			throw new IllegalStateException(
					"Can not get service instances from nacos, serviceId=" + serviceId,
					e);
		}
	}

	private List<NacosServer> instancesToServerList(List<Instance> instances) {
		List<NacosServer> result = new ArrayList<>();
		if (null == instances) {
			return result;
		}
		for (Instance instance : instances) {
			result.add(new NacosServer(instance));
		}

		return result;
	}

	public String getServiceId() {
		return serviceId;
	}

	@Override
	public void initWithNiwsConfig(IClientConfig iClientConfig) {
		this.serviceId = iClientConfig.getClientName();
	}
}

protected final ServerListUpdater.UpdateAction updateAction = new ServerListUpdater.UpdateAction() {
        @Override
        public void doUpdate() {
            updateListOfServers();
        }
    };

public DynamicServerListLoadBalancer(IClientConfig clientConfig) {
	initWithNiwsConfig(clientConfig);
}
    
@Override
public void initWithNiwsConfig(IClientConfig clientConfig) {
	try {
		super.initWithNiwsConfig(clientConfig);
		String niwsServerListClassName = clientConfig.getPropertyAsString( CommonClientConfigKey.NIWSServerListClassName, DefaultClientConfigImpl.DEFAULT_SEVER_LIST_CLASS);
		ServerList<T> niwsServerListImpl = (ServerList<T>) ClientFactory
                    .instantiateInstanceWithClientConfig(niwsServerListClassName, clientConfig);
                //得到所有的server实现
		this.serverListImpl = niwsServerListImpl;

                
		if (niwsServerListImpl instanceof AbstractServerList) {
			AbstractServerListFilter<T> niwsFilter = ((AbstractServerList) niwsServerListImpl)
                        .getFilterImpl(clientConfig);
			niwsFilter.setLoadBalancerStats(getLoadBalancerStats());
			this.filter = niwsFilter;
		}

    
		String serverListUpdaterClassName = clientConfig.getPropertyAsString( CommonClientConfigKey.ServerListUpdaterClassName, DefaultClientConfigImpl.DEFAULT_SERVER_LIST_UPDATER_CLASS);

               // 获取Updater对象
		this.serverListUpdater = (ServerListUpdater) ClientFactory.instantiateInstanceWithClientConfig(serverListUpdaterClassName, clientConfig);

  
		restOfInit(clientConfig);
	} catch (Exception e) {
		throw new RuntimeException(
                    "Exception while initializing NIWSDiscoveryLoadBalancer:"
                            + clientConfig.getClientName()
                            + ", niwsClientConfig:" + clientConfig, e);
	}
}

void restOfInit(IClientConfig clientConfig) {
	boolean primeConnection = this.isEnablePrimingConnections();
	// turn this off to avoid duplicated asynchronous priming done in BaseLoadBalancer.setServerList()
	this.setEnablePrimingConnections(false);
        //采用定时任务进行定时刷新实例信息缓存
	enableAndInitLearnNewServersFeature();//最重要的点

        //进行一次实例拉取操作
	updateListOfServers();
	if (primeConnection && this.getPrimeConnections() != null) {
		this.getPrimeConnections() .primeConnections(getReachableServers());
	}
	this.setEnablePrimingConnections(primeConnection);
	LOGGER.info("DynamicServerListLoadBalancer for client {} initialized: {}", clientConfig.getClientName(), this.toString());
}

// 这里就是进行实例信息缓存更新的操作
@VisibleForTesting
public void updateListOfServers() {
	List<T> servers = new ArrayList<T>();
	if (serverListImpl != null) {
    // 调用拉取新实例信息的方法
		servers = serverListImpl.getUpdatedListOfServers();
		LOGGER.debug("List of Servers for {} obtained from Discovery client: {}", getIdentifier(), servers);

    // 用Filter对拉取的servers列表进行更新
		if (filter != null) {
			servers = filter.getFilteredListOfServers(servers);
			LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}", getIdentifier(), servers);
		}
	}
  // 更新实例列表
	updateAllServerList(servers);
}

之后我们看最重要的enableAndInitLearnNewServersFeature这个方法的操作

@Override
public synchronized void start(final UpdateAction updateAction) {
	if (isActive.compareAndSet(false, true)) {
		final Runnable wrapperRunnable = new Runnable() {
			@Override
			public void run() {
				if (!isActive.get()) {
					if (scheduledFuture != null) {
						scheduledFuture.cancel(true);
					}
					return;
				}
				try {
                                        // 这里就是在DynamicServerListLoadBalancer中的Servers实现
					updateAction.doUpdate();
					lastUpdated = System.currentTimeMillis();
				} catch (Exception e) {
					logger.warn("Failed one update cycle", e);
				}
			}
		};

                // 默认定时任务执行时间间隔为30s
		scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(
                    wrapperRunnable,
                    initialDelayMs,
                    refreshIntervalMs,
                    TimeUnit.MILLISECONDS);
	} else {
		logger.info("Already active, no-op");
	}
}