????问题描述 dubbo消费端一直不停重试reconnect dubbo provider, 并报错；
[DUBBO] Fail to connect to HeaderExchangeClient [channel=org.apache.dubbo.remoting.transport.netty4.NettyClient [10.1.1.12:0 -> /10.1.1.228:20888]], dubbo version: 2.7.3, current host: 10.1.1.122019-08-30 20:33:52.283 [/] httpwrapper [dubbo-client-idleCheck-thread-1] ERROR o.a.d.r.e.s.h.ReconnectTimerTask - [DUBBO] Fail to connect to HeaderExchangeClient [channel=org.apache.dubbo.remoting.transport.netty4.NettyClient [10.1.1.12:0 -> /10.1.1.228:20888]], dubbo version: 2.7.3, current host: 10.1.1.12 org.apache.dubbo.remoting.RemotingException: client(url: dubbo://10.1.1.228:20888/com.cxq56.service.GeoService?actives=0&anyhost=true&application=httpwrapper&async=false&bean.name=providers:dubbo:com.cxq56.service.GeoService&check=false&cluster=failover&codec=dubbo&default.deprecated=false&default.dynamic=false&default.register=true&default.retries=1&default.timeout=10000&deprecated=false&dubbo=2.0.2&dynamic=false&generic=false&heartbeat=60000&interface=com.cxq56.service.GeoService&lazy=false&loadbalance=random&methods=createForbiddenGeo,calculatedDistance,createSiteInfo,getSiteAndDistance,getAllGeoByCityId,searchForPOI,createGeo&pid=1&qos.enable=false®ister=true®ister.ip=10.1.1.12&release=2.7.1&remote.application=geo-provider&retries=0&revision=1.0-SNAPSHOT&shutwait=40000&side=consumer&sticky=false&timeout=3000×tamp=1567049198218&validation=false) failed to connect to server /10.1.1.228:20888 client-side timeout 3000ms (elapsed: 3000ms) from netty client 10.1.1.12 using dubbo version 2.7.3at org.apache.dubbo.remoting.transport.netty4.NettyClient.doConnect(NettyClient.java:171)at org.apache.dubbo.remoting.transport.AbstractClient.connect(AbstractClient.java:190)at org.apache.dubbo.remoting.transport.AbstractClient.reconnect(AbstractClient.java:246)at org.apache.dubbo.remoting.exchange.support.header.HeaderExchangeClient.reconnect(HeaderExchangeClient.java:155)at org.apache.dubbo.remoting.exchange.support.header.ReconnectTimerTask.doTask(ReconnectTimerTask.java:49)at org.apache.dubbo.remoting.exchange.support.header.AbstractTimerTask.run(AbstractTimerTask.java:87)at org.apache.dubbo.common.timer.HashedWheelTimer$HashedWheelTimeout.expire(HashedWheelTimer.java:648)at org.apache.dubbo.common.timer.HashedWheelTimer$HashedWheelBucket.expireTimeouts(HashedWheelTimer.java:727)at org.apache.dubbo.common.timer.HashedWheelTimer$Worker.run(HashedWheelTimer.java:449)at java.lang.Thread.run(Thread.java:748)
????经过查看，provider的ip并不在线上集群，但是在redis注册中心中还存在，说明是没有实现优雅停机导致，provider注册数据没有删掉，但是其他provider服务都没有问题，只有这个provider会被一直reconnect；这就很让人头疼了，因为一直抛异常。
????背景：dubbo有连个机制来保证服务的可用性，一个是心跳机制，探测对方是否存活； 一个是重连机制；这两个定时探测机制都是通过HeaderExchangeClient类来初始化的；
private final Client client; private final ExchangeChannel channel; private static final HashedWheelTimer IDLE_CHECK_TIMER = new HashedWheelTimer( new NamedThreadFactory("dubbo-client-idleCheck", true), 1, TimeUnit.SECONDS, TICKS_PER_WHEEL); private HeartbeatTimerTask heartBeatTimerTask; private ReconnectTimerTask reconnectTimerTask; public HeaderExchangeClient(Client client, boolean startTimer) { Assert.notNull(client, "Client can't be null"); this.client = client; this.channel = new HeaderExchangeChannel(client); if (startTimer) { URL url = client.getUrl(); startReconnectTask(url); startHeartBeatTask(url); } } ????可以看到使用的是HashedWheelTimer来定时轮询的；这里的reConnectTask如果失败，就会打印出我们的异常日志；而且失败后不会停止重试，会一直尝试下去；那么这里有一个问题，是否redis有的历史注册信息，consumer都会去尝试reconnect呢？
????所以我们尝试打个断点尝试分析一下；并往上追述可以发现当dubbo consumer启动时会在redis中注册本身的消费端信息，同时也会通过接口名获取所有provider注册信息，并在RedisRegistery.class中进行过滤，代码如下：
private void doNotify(Jedis jedis, Collection<String> keys, URL url, Collection<NotifyListener> listeners) { if (keys == null || keys.isEmpty() || listeners == null || listeners.isEmpty()) { return; } long now = System.currentTimeMillis(); List<URL> result = new ArrayList<>(); List<String> categories = Arrays.asList(url.getParameter(CATEGORY_KEY, new String[0])); String consumerService = url.getServiceInterface(); for (String key : keys) { if (!ANY_VALUE.equals(consumerService)) { String providerService = toServiceName(key); if (!providerService.equals(consumerService)) { continue; } } String category = toCategoryName(key); if (!categories.contains(ANY_VALUE) && !categories.contains(category)) { continue; } List<URL> urls = new ArrayList<>(); Map<String, String> values = jedis.hgetAll(key); if (CollectionUtils.isNotEmptyMap(values)) { for (Map.Entry<String, String> entry : values.entrySet()) { URL u = URL.valueOf(entry.getKey()); //如果dynamic为false 或者 过期时间 大于 当前时间 就加入这个注册url，后面进行reconnect if (!u.getParameter(DYNAMIC_KEY, true) || Long.parseLong(entry.getValue()) >= now) { if (UrlUtils.isMatch(url, u)) { urls.add(u); } } } } if (urls.isEmpty()) { urls.add(URLBuilder.from(url) .setProtocol(EMPTY_PROTOCOL) .setAddress(ANYHOST_VALUE) .setPath(toServiceName(key)) .addParameter(CATEGORY_KEY, category) .build()); } result.addAll(urls); if (logger.isInfoEnabled()) { logger.info("redis notify: " + key + " = " + urls); } } if (CollectionUtils.isEmpty(result)) { return; } for (NotifyListener listener : listeners) { notify(url, listener, result); } } ????provider注册信息的过滤条件是，dynamic为true且过期时间小于当前时间，一般旧的注册数据的过期时间肯定都会小于当前时间（这种数据算是脏数据，优雅停机和dubbo monitor都可以移除），源头就在这个dynamic上，由于这个provider使用的dubbo版本是2.7.1，有一个bug，默认的dynamic的值为false，直接导致现在的问题；另外这个dynamic的官方文档解释的意思是 "服务是否动态注册，如果设为false，注册后将显示后disable状态，需人工启用，并且服务提供者停止时，也不会自动取消册，需人工禁用。" 但是并没有说，consumer会一直重连。
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