Ribbon服务实例选择与更新机制

梦里梦外; 2021-06-10 20:40 353阅读 0赞

## 简介 ##

用来了解下Ribbon选择服务实例和服务实例列表更新机制；

## 选择服务实例 ##

![服务实例选择][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hleWl3dXd1_size_16_color_FFFFFF_t_70]涉及到如下几个类：

*  1.ILoadBalancer:负载均衡对象，用于封装ServerList；
 *  2.IRule：实例选择规则对象，决定采用何种规则进行实例选择;
 *  3.Predicate:断言类，选择规则的具体实现；
 *  4.LoadBalancerStats:用于保存实例状态的缓存类；

## 更新过程 ##

Ribbon更新服务实例主要依靠的对象有:

*  PollingServerListUpdater:该对象是用来更新服务实例包装类，其该类启动时通过初始化一个LazyHolder，LazyHolder是一个定时任务Excutor的包装类，该Executor会定时调用updateAction.doUpdate()方法进行service instance更新，源码如下：

@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 {
                            updateAction.doUpdate();//服务实例更新
                            lastUpdated = System.currentTimeMillis();
                        } catch (Exception e) {
                            logger.warn("Failed one update cycle", e);
                        }
                    }
                };
    //获取定时Executor进行任务调度
                scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(
                        wrapperRunnable,
                        initialDelayMs,
                        refreshIntervalMs,
                        TimeUnit.MILLISECONDS
                );
            } else {
                logger.info("Already active, no-op");
            }
        }

*  ServerListUpdater.UpdateAction源码如下:

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

*  ServerList的具体实现类serverListImpl进行服务实例更新:

@VisibleForTesting
        public void updateListOfServers() {
            List<T> servers = new ArrayList<T>();
            if (serverListImpl != null) {
               //获取最新服务实例
                servers = serverListImpl.getUpdatedListOfServers();
                LOGGER.debug("List of Servers for {} obtained from Discovery client: {}",
                        getIdentifier(), servers);
    
                if (filter != null) {
                    servers = filter.getFilteredListOfServers(servers);
                    LOGGER.debug("Filtered List of Servers for {} obtained from Discovery client: {}",
                            getIdentifier(), servers);
                }
            }
            updateAllServerList(servers);
        }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hleWl3dXd1_size_16_color_FFFFFF_t_70]: /images/20210527/47b976bd715046ae8ef7c645d03629f3.png