现在研究下Eureka服务下线的源码。由服务续约的源码我们知道，如果客户端在90秒内没有继续跟服务端进行心跳的话，服务端会进行下线客户端并且更改状态将其剔除，并且也会在集群中告知（同步）其它节点。
〓Eureka Client
/**
* 注销服务，调用client的cancel服务，往里面看也就是调用了服务端的http delete 请求进行服务下线
*/ void unregister() {
// It can be null if shouldRegisterWithEureka == false if(eurekaTransport != null && eurekaTransport.registrationClient != null) {
try {
logger.info("Unregistering ...");
EurekaHttpResponse<Void> httpResponse = eurekaTransport.registrationClient.cancel(instanceInfo.getAppName(), instanceInfo.getId());
logger.info(PREFIX + appPathIdentifier + " - deregister status: " + httpResponse.getStatusCode());
} catch (Exception e) {
logger.error(PREFIX + appPathIdentifier + " - de-registration failed" + e.getMessage(), e);
}
}
}
@Override public EurekaHttpResponse<Void> cancel(String appName, String id) {
String urlPath = "apps/" + appName + '/' + id;
ClientResponse response = null;
try {
Builder resourceBuilder = jerseyClient.resource(serviceUrl).path(urlPath).getRequestBuilder();
addExtraHeaders(resourceBuilder);
response = resourceBuilder.delete(ClientResponse.class);
return anEurekaHttpResponse(response.getStatus()).headers(headersOf(response)).build();
} finally {
if (logger.isDebugEnabled()) {
logger.debug("Jersey HTTP DELETE {}/{}; statusCode={}", serviceUrl, urlPath, response == null ? "N/A" : response.getStatus());
}
if (response != null) {
response.close();
}
}
}
接下来再看是哪里调用注销服务：
@PreDestroy @Override public synchronized void shutdown() {
if (isShutdown.compareAndSet(false, true)) {
logger.info("Shutting down DiscoveryClient ...");
// 注销服务状态的监听器 if (statusChangeListener != null && applicationInfoManager != null) {
applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
}
// 取消定时器任务，关闭线程池等 cancelScheduledTasks();
// 服务实例以及被注册，那么设置实例状态为DOWN，并且进行注销操作 if (applicationInfoManager != null && clientConfig.shouldRegisterWithEureka()) {
applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
unregister();
}
// 关闭eurekaTransport if (eurekaTransport != null) {
eurekaTransport.shutdown();
}
// 关闭监控 heartbeatStalenessMonitor.shutdown();
registryStalenessMonitor.shutdown();
logger.info("Completed shut down of DiscoveryClient");
}
}
// DiscoveryManager调用了DiscveryClient的shutdown方法，这里就是服务下线的入口 public void shutdownComponent() {
if (discoveryClient != null) {
try {
discoveryClient.shutdown();
discoveryClient = null;
} catch (Throwable th) {
logger.error("Error in shutting down client", th);
}
}
}
〓Eureka Server
// 服务端提供的对外服务下线接口 @DELETE public Response cancelLease(
@HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
boolean isSuccess = registry.cancel(app.getName(), id,
"true".equals(isReplication));
if (isSuccess) {
logger.debug("Found (Cancel): " + app.getName() + " - " + id);
return Response.ok().build();
} else {
logger.info("Not Found (Cancel): " + app.getName() + " - " + id);
return Response.status(Status.NOT_FOUND).build();
}
}
// 服务端下线入口 @Override public boolean cancel(final String appName, final String id,
final boolean isReplication) {
// 调用父类cancel方法，将实例信息添加到最近下线队列、最近变更队列，并且使本地缓存失效操作 if (super.cancel(appName, id, isReplication)) {
// 服务端集群之间进行Cancel同步操作 replicateToPeers(Action.Cancel, appName, id, null, null, isReplication);
synchronized (lock) {
if (this.expectedNumberOfRenewsPerMin > 0) {
// Since the client wants to cancel it, reduce the threshold (1 for 30 seconds, 2 for a minute) this.expectedNumberOfRenewsPerMin = this.expectedNumberOfRenewsPerMin - 2;
this.numberOfRenewsPerMinThreshold =
(int) (this.expectedNumberOfRenewsPerMin * serverConfig.getRenewalPercentThreshold());
}
}
return true;
}
return false;
}
// 最终调用这个方法进行实例信息移除 protected boolean internalCancel(String appName, String id, boolean isReplication) {
try {
// 读锁 read.lock();
// 取消（下线）计数 CANCEL.increment(isReplication);
// 获取续约实例 Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
Lease<InstanceInfo> leaseToCancel = null;
if (gMap != null) {
leaseToCancel = gMap.remove(id);
}
// 添加到近期取消队列 recentCanceledQueue.add(new Pair<Long, String>(System.currentTimeMillis(), appName + "(" + id + ")"));
// 移除实例状态 InstanceStatus instanceStatus = overriddenInstanceStatusMap.remove(id);
if (instanceStatus != null) {
logger.debug("Removed instance id {} from the overridden map which has value {}", id, instanceStatus.name());
}
if (leaseToCancel == null) {
// 续约实例不存在，返回false CANCEL_NOT_FOUND.increment(isReplication);
logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
return false;
} else {
// 续约实例执行取消操作：设置剔除时间 leaseToCancel.cancel();
InstanceInfo instanceInfo = leaseToCancel.getHolder();
String vip = null;
String svip = null;
if (instanceInfo != null) {
// 设置实例行为为delete instanceInfo.setActionType(ActionType.DELETED);
// 添加到近期变化队列 recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
instanceInfo.setLastUpdatedTimestamp();
vip = instanceInfo.getVIPAddress();
svip = instanceInfo.getSecureVipAddress();
}
// 使响应缓存失效 invalidateCache(appName, vip, svip);
logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
return true;
}
} finally {
// 释放读锁 read.unlock();
}
}
总结
Eureka client执行DiscoveryManager调用了DiscveryClient的shutdown方法进行服务的下线操作，然后服务端接收到http delete请求之后进行服务的相关下线操作，并且同步到集群中的其它节点。Eureka server则会将实例信息进行剔除处理，并且添加到近期变化队列和近期取消队列里。
