【Java】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方法。调用的是InstanceRegistry.renew方法。

@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);
//其他略
return response;
}

InstanceRegistry.renew会发一个EventPublish的续约监听（代码略），然后调用PeerAwareInstanceRegistryImpl#renew。PeerAwareInstanceRegistryImpl#renew。会调用AbstractInstanceRegistry#renew，如果成功，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 {
// 其他略
renewsLastMin.increment();
leaseToRenew.renew();
return true;
}
}

Lease#renew，更新lastUpdateTimestamp时间。

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

综上，续约就是更改lastUpdateTimestamp的时间。

注册

注册调用的是server的ApplicationResource#addInstance，他调用InstanceRegistry#register，和上面一样，这个会发布注册监听。

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

InstanceRegistry#register会调用PeerAwareInstanceRegistryImpl#register，实际的注册是AbstractInstanceRegistry#register方法，这个方法在Eureka - Server服务启动已经提过了，这里略。注册成功后，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，然后他会调用InstanceRegistry#cancel（代码略）发布下线监听。

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

InstanceRegistry#cancel调用PeerAwareInstanceRegistryImpl#cancel，下线成功后，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，这个是核心代码。这里会设置取消时间戳，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 {
//其他略
// 设置取消的时间戳
leaseToCancel.cancel();
//其他略
// 过期缓存，这里是读写缓存
invalidateCache(appName, vip, svip);
}
} finally {
read.unlock();
}
// 用于自我保护
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，他会清除过期的实例，他也会调用AbstractInstanceRegistry#internalCancel方法，所以读写缓存的图更改为：
【Java】Eureka - 服务续约和注册、下线(Server)

bug

我们看到，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));
}

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