Eureka源码解析 - Eureka Server-集群同步 - 《Java 相关》

下面分析下Eureka Server的集群同步，先看关键代码

registry.register(info, "true".equals(isReplication));

其中关键字段 isReplication表示是否来自于集群同步
假如现在有3个Eureka server集群，3个user集群服务，3个product集群服务。
当user服务启动时向其中某个Eureka Server注册时，注册完毕后会将同步注册信息给其他的Eureka Server，为了防止产生死循环（也即第二个服务收到注册信息后又重复发给第一个服务器），即引入了isReplication字段。
当User服务向Eureka Server注册时，isReplication为null，而服务器同步时isReplication为true。

public void register(final InstanceInfo info, final boolean isReplication) {
        int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
        if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
            leaseDuration = info.getLeaseInfo().getDurationInSecs();
        }
        super.register(info, leaseDuration, isReplication);
        replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
    }

集群同步

private void replicateToPeers(Action action, String appName, String id,
                                  InstanceInfo info /* optional */,
                                  InstanceStatus newStatus /* optional */, boolean isReplication) {
        Stopwatch tracer = action.getTimer().start();
        try {
            if (isReplication) {
                numberOfReplicationsLastMin.increment();
            }
            // If it is a replication already, do not replicate again as this will create a poison replication
            // isReplication 如果为true则直接返回，不用同步
            if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
                return;
            }
            for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
                // If the url represents this host, do not replicate to yourself.
                if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
                    // 如果没有集群也跳过同步，这种情况是没有Eureka Server集群
                    continue;
                }
                // 同步注册信息给其他服务器
                replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
            }
        } finally {
            tracer.stop();
        }
    }

public void register(final InstanceInfo info, final boolean isReplication) {
        int leaseDuration = Lease.DEFAULT_DURATION_IN_SECS;
        if (info.getLeaseInfo() != null && info.getLeaseInfo().getDurationInSecs() > 0) {
            leaseDuration = info.getLeaseInfo().getDurationInSecs();
        }
        super.register(info, leaseDuration, isReplication);
        replicateToPeers(Action.Register, info.getAppName(), info.getId(), info, null, isReplication);
    }

集群同步

private void replicateToPeers(Action action, String appName, String id,
                                  InstanceInfo info /* optional */,
                                  InstanceStatus newStatus /* optional */, boolean isReplication) {
        Stopwatch tracer = action.getTimer().start();
        try {
            if (isReplication) {
                numberOfReplicationsLastMin.increment();
            }
            // If it is a replication already, do not replicate again as this will create a poison replication
            // isReplication 如果为true则直接返回，不用同步
            if (peerEurekaNodes == Collections.EMPTY_LIST || isReplication) {
                return;
            }
            for (final PeerEurekaNode node : peerEurekaNodes.getPeerEurekaNodes()) {
                // If the url represents this host, do not replicate to yourself.
                if (peerEurekaNodes.isThisMyUrl(node.getServiceUrl())) {
                    // 如果没有集群也跳过同步，这种情况是没有Eureka Server集群
                    continue;
                }
                // 同步注册信息给其他服务器
                replicateInstanceActionsToPeers(action, appName, id, info, newStatus, node);
            }
        } finally {
            tracer.stop();
        }
    }

两种情况是不用同步

isReplication为true，即来自集群间同步请求
只有一个单一的Eureka Server服务器