基于Nacos服务地址动态感知原理实现ribbon远程调用平滑上下线

背景

远程调用一般都会用ribbon，尽管使用feign，还是用的ribbon做的负载均衡，远程调用。但是ribbon会每隔30s刷新注册表信息，这样就会导致如果服务下线了，由于注册表没有及时更新，那远程调用就会报错。我们看下默认ribbon实现。

1. com.netflix.loadbalancer.PollingServerListUpdater 这个类是ribbon更新注册表的核心类。

nacos 动态更新地址原理

Nacos客户端中有一个HostReactor类，它的功能是实现服务的动态更新，基本原理是：

• 客户端发起时间订阅后，在HostReactor中有一个UpdateTask线程，每10s发送一次Pull请求，获得服务端最新的地址列表
• 对于服务端，它和服务提供者的实例之间维持了心跳检测，一旦服务提供者出现异常，则会发送一个Push消息给Nacos客户端，也就是服务端消费者
• 服务消费者收到请求之后，使用HostReactor中提供的processServiceJSON解析消息，并更新本地服务地址列表

改造ribbon默认更新策略

基于上面的理论，是不是可以监听nacos事件更新事件，如果有更新，就重新刷新下ribbon的注册表。

1. 覆盖ServerListUpdater,自己定义一个NacosDynamicServerListUpdater代码如下；

public class NacosDynamicServerListUpdater implements ServerListUpdater {
    private static Logger log = LoggerFactory.getLogger(NacosDynamicServerListUpdater.class);

    private CopyOnWriteArrayList<LBUpdater> lbUpdaters = new CopyOnWriteArrayList();

    private NamingService namingService;

    @Value("${ribbon.PollingServerListUpdater.initial-delay:1000}")
    private long initialDelay;
    @Value("${ribbon.PollingServerListUpdater.refresh-interval:30000}")
    private long refreshInterval;

    private NacosDiscoveryProperties properties;

    public NacosDynamicServerListUpdater(NamingService namingService, NacosDiscoveryProperties properties) {
        this.namingService = namingService;
        this.properties = properties;
    }

    @Override
    public void start(UpdateAction updateAction) {
        NacosDynamicServerListUpdater.LBUpdater lbUpdater = new NacosDynamicServerListUpdater.LBUpdater(updateAction);
        this.lbUpdaters.add(lbUpdater);
        lbUpdater.start();
        log.info("nacos dslu-started: {}, lbUpdater: {}, PollingServerListUpdater: initialDelay={}, refreshInterval={}",
                new Object[]{this, lbUpdater.getIdentity(), this.initialDelay, this.refreshInterval});
    }

    @Override
    public void stop() {
        log.info("nacos dslu-stopped: {}", this);
        Iterator iterator = this.lbUpdaters.iterator();

        while (iterator.hasNext()) {
            NacosDynamicServerListUpdater.LBUpdater lbUpdater = (NacosDynamicServerListUpdater.LBUpdater) iterator.next();

            try {
                lbUpdater.stop();
            } catch (Exception var4) {
                log.error("nacos dslu-stop-lbUpdater: " + lbUpdater.getIdentity(), var4);
            }
        }
    }

    @Override
    public String getLastUpdate() {
        return null;
    }

    @Override
    public long getDurationSinceLastUpdateMs() {
        return 0;
    }

    @Override
    public int getNumberMissedCycles() {
        return 0;
    }

    @Override
    public int getCoreThreads() {
        return 0;
    }

    class LBUpdater {
        Logger log = LoggerFactory.getLogger(NacosDynamicServerListUpdater.LBUpdater.class);
        private String serviceId;
        private volatile UpdateAction updateAction;
        private volatile BaseLoadBalancer lb;
        private NacosDynamicServerListWatcher nacosWatcher;
        private PollingServerListUpdater pollingServerListUpdater;
        private String identity;

        public LBUpdater(UpdateAction updateAction) {
            this.updateAction = updateAction;
            this.lb = this.getLoadBalancer(updateAction);
            this.serviceId = this.lb.getClientConfig().getClientName();
            this.pollingServerListUpdater = new PollingServerListUpdater(NacosDynamicServerListUpdater.this.initialDelay, NacosDynamicServerListUpdater.this.refreshInterval);
            this.nacosWatcher = new NacosDynamicServerListWatcher(NacosDynamicServerListUpdater.this.namingService, NacosDynamicServerListUpdater.this.properties, this);
        }

        public void start() {
            this.pollingServerListUpdater.start(this.updateAction);
            this.nacosWatcher.startWatch();
        }

        private BaseLoadBalancer getLoadBalancer(UpdateAction updateAction) {
            try {
                Class<?> bc = updateAction.getClass();
                Field field = bc.getDeclaredField("this$0");
                field.setAccessible(true);
                return (BaseLoadBalancer) field.get(updateAction);
            } catch (Exception var4) {
                this.log.error("nacos dslu-getlb", var4);
                throw new IllegalStateException("Not supported LB used", var4);
            }
        }

        public String getServiceId() {
            return this.serviceId;
        }

        public UpdateAction getUpdateAction() {
            return this.updateAction;
        }

        public BaseLoadBalancer getLb() {
            return this.lb;
        }

        public PollingServerListUpdater getPollingServerListUpdater() {
            return this.pollingServerListUpdater;
        }

        public NacosDynamicServerListWatcher getNacosWatcher() {
            return nacosWatcher;
        }

        public String getIdentity() {
            if (this.identity == null) {
                this.identity = String.format("{serviceId: %s, lb: %s, updateAction: %s}", this.getServiceId(), this.getLb().hashCode(), this.getUpdateAction().hashCode());
            }

            return this.identity;
        }

        public void stop() {
            try {
                this.nacosWatcher.stop();
            } catch (Exception e) {
                this.log.error("nacos dslu-stop-watcher: " + this.getIdentity(), e);
            }

            this.pollingServerListUpdater.stop();
        }

        public void doUpdate() {
            this.getUpdateAction().doUpdate();
            this.log.info("nacos dslu-doUpdate: {}", this.getIdentity());
            this.serviceLog();

        }

        private void serviceLog() {
            List<Server> backwardList = this.getLb().getAllServers();
            StringBuilder serviceLog = new StringBuilder("");
            Iterator iterator = backwardList.iterator();

            while (iterator.hasNext()) {
                Server service = (Server) iterator.next();
                serviceLog.append(service.getHost());
                serviceLog.append(":");
                serviceLog.append(service.getPort());
                serviceLog.append(",");
            }

            this.log.info("[nacos dslu-LbServerList] [{}].{}", serviceLog, this.getIdentity());
        }
    }
}

2. 定义一个nacos的监听类NacosDynamicServerListWatcher，用于监听更新事件

public class NacosDynamicServerListWatcher {
    private static Logger log = LoggerFactory.getLogger(NacosDynamicServerListWatcher.class);

    private NamingService namingService;

    private final NacosDiscoveryProperties properties;
    private NacosDynamicServerListUpdater.LBUpdater lbUpdater;

    public NacosDynamicServerListWatcher(NamingService namingService, NacosDiscoveryProperties properties, NacosDynamicServerListUpdater.LBUpdater lbUpdater) {
        this.namingService = namingService;
        this.properties = properties;
        this.lbUpdater = lbUpdater;
    }

    public void startWatch() {

        log.info("nacos dslw-start: {}, serviceName: {}", this.lbUpdater.getIdentity(), lbUpdater.getServiceId());

        try {
            namingService.subscribe(lbUpdater.getServiceId(), Arrays.asList(properties.getClusterName()), event -> {
                if (event instanceof NamingEvent) {
                    NamingEvent namingEvent = (NamingEvent) event;
                    System.out.println("服务名：" + namingEvent.getServiceName());
                    System.out.println("实例：" + namingEvent.getInstances());
                    lbUpdater.doUpdate();
                }
            });
        } catch (NacosException e) {
            e.printStackTrace();
        }
    }

    public void stop() {

    }
}

3. 定义配置类，让springboot启动时自动加载

@Configuration
@ConditionalOnRibbonNacos
public class NacosDynamicServerListConfiguration {
    @Bean
    public NacosDynamicServerListUpdater dynamicServerListUpdater(NacosDiscoveryProperties properties) throws NacosException {
        return new NacosDynamicServerListUpdater(NacosFactory.createNamingService(properties.getServerAddr()), properties);
    }

}

4. 修改spring.factories

测试

1. 启动service-feign、service-hi服务
2. 关闭service-hi服务可以看到如下日志：

参考文章

超硬核，Nacos实现原理详细讲解