关于eureka:Eureka-服务续约和注册下线Server

续约

续约的时候，调用的是服务端的InstanceResource#renewLease办法。调用的是InstanceRegistry.renew办法。

@PUT
public Response renewLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication,
        @QueryParam("overriddenstatus") String overriddenStatus,
        @QueryParam("status") String status,
        @QueryParam("lastDirtyTimestamp") String lastDirtyTimestamp) {
    boolean isFromReplicaNode = "true".equals(isReplication);
    boolean isSuccess = registry.renew(app.getName(), id, isFromReplicaNode);

    //其余略
    return response;
}

InstanceRegistry.renew会发一个EventPublish的续约监听（代码略），而后调用PeerAwareInstanceRegistryImpl#renew。PeerAwareInstanceRegistryImpl#renew。会调用AbstractInstanceRegistry#renew，如果胜利，会进行节点间的复制。

public boolean renew(final String appName, final String id, final boolean isReplication) {
    if (super.renew(appName, id, isReplication)) {
        replicateToPeers(Action.Heartbeat, appName, id, null, null, isReplication);
        return true;
    }
    return false;
}

AbstractInstanceRegistry#renew，获取续约，如果有的话。

public boolean renew(String appName, String id, boolean isReplication) {
    RENEW.increment(isReplication);
    Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
    Lease<InstanceInfo> leaseToRenew = null;
    if (gMap != null) {
        leaseToRenew = gMap.get(id);
    }
    if (leaseToRenew == null) {
        RENEW_NOT_FOUND.increment(isReplication);
        logger.warn("DS: Registry: lease doesn't exist, registering resource: {} - {}", appName, id);
        return false;
    } else {
        // 其余略
        renewsLastMin.increment();
        leaseToRenew.renew();
        return true;
    }
}

Lease#renew，更新lastUpdateTimestamp工夫。

public void renew() {
    lastUpdateTimestamp = System.currentTimeMillis() + duration;
}

综上，续约就是更改lastUpdateTimestamp的工夫。

注册

注册调用的是server的ApplicationResource#addInstance，他调用InstanceRegistry#register，和下面一样，这个会公布注册监听。

public Response addInstance(InstanceInfo info,
                                @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    //其余略
    registry.register(info, "true".equals(isReplication));
    return Response.status(204).build();  // 204 to be backwards compatible
}

InstanceRegistry#register会调用PeerAwareInstanceRegistryImpl#register，理论的注册是AbstractInstanceRegistry#register办法，这个办法在Eureka – Server服务启动曾经提过了，这里略。注册胜利后，会进行节点间的复制。

@Override
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);
}

下线

下线调用的是InstanceResource#cancelLease，而后他会调用InstanceRegistry#cancel（代码略）公布下线监听。

@DELETE
public Response cancelLease(
        @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
    //其余略
    boolean isSuccess = registry.cancel(app.getName(), id,
            "true".equals(isReplication));
    //其余略
}

InstanceRegistry#cancel调用PeerAwareInstanceRegistryImpl#cancel，下线胜利后，会进行节点间的复制。

@Override
public boolean cancel(final String appName, final String id,
                      final boolean isReplication) {
    if (super.cancel(appName, id, isReplication)) {
        replicateToPeers(Action.Cancel, appName, id, null, null, isReplication);

        return true;
    }
    return false;
}

AbstractInstanceRegistry#cancel会调用AbstractInstanceRegistry#internalCancel，这个是外围代码。这里会设置勾销工夫戳，并过期读写缓存。

@Override
public boolean cancel(String appName, String id, boolean isReplication) {
    return internalCancel(appName, id, isReplication);
}


protected boolean internalCancel(String appName, String id, boolean isReplication) {
    read.lock();
    try {
        //其余略
        // 设置勾销的工夫戳
        leaseToCancel.cancel();
        //其余略
        // 过期缓存，这里是读写缓存
        invalidateCache(appName, vip, svip);    
        }
    } finally {
        read.unlock();
    }
    // 用于自我爱护
    synchronized (lock) {
        if (this.expectedNumberOfClientsSendingRenews > 0) {
            // Since the client wants to cancel it, reduce the number of clients to send renews.
            this.expectedNumberOfClientsSendingRenews = this.expectedNumberOfClientsSendingRenews - 1;
            updateRenewsPerMinThreshold();
        }
    }

    return true;
}

另外，Eureka – Server服务启动提到了EvictionTask#run，他会革除过期的实例，他也会调用AbstractInstanceRegistry#internalCancel办法，所以读写缓存的图更改为：

bug

咱们看到，续约的时候lastUpdateTimestamp = System.currentTimeMillis() + duration;，判断是否过期的时候，又加了一个duration，所以他剔除的并不是90秒没有心跳的，而是180秒没有心跳的。

public boolean isExpired(long additionalLeaseMs) {
    return (evictionTimestamp > 0 || System.currentTimeMillis() > (lastUpdateTimestamp + duration + additionalLeaseMs));
}