我们知道，在Eureka中，可以使用如下方法使Eureka主动下线，那么本篇文章就来分析一下子这个下线的流程

public synchronized void shutdown() {
        if (isShutdown.compareAndSet(false, true)) {
            logger.info("Shutting down DiscoveryClient ...");

            if (statusChangeListener != null && applicationInfoManager != null) {
                applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
            }

            cancelScheduledTasks();

            // If APPINFO was registered
            if (applicationInfoManager != null
                    && clientConfig.shouldRegisterWithEureka()
                    && clientConfig.shouldUnregisterOnShutdown()) {
                applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
                unregister();
            }

            if (eurekaTransport != null) {
                eurekaTransport.shutdown();
            }

            heartbeatStalenessMonitor.shutdown();
            registryStalenessMonitor.shutdown();

            logger.info("Completed shut down of DiscoveryClient");
        }
    }

主要做了这么几件事：

1. 解除状态监听器
2. 取消心跳、刷新线程

private void cancelScheduledTasks() {
        if (instanceInfoReplicator != null) {
            instanceInfoReplicator.stop();
        }
        if (heartbeatExecutor != null) {
            heartbeatExecutor.shutdownNow();
        }
        if (cacheRefreshExecutor != null) {
            cacheRefreshExecutor.shutdownNow();
        }
        if (scheduler != null) {
            scheduler.shutdownNow();
        }
    }

1. 向服务端发起下线通知

 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 + "{} - deregister  status: {}", appPathIdentifier, httpResponse.getStatusCode());
            } catch (Exception e) {
                logger.error(PREFIX + "{} - de-registration failed{}", appPathIdentifier, 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();
            }
        }
    }

1. 停止各个监听器

服务端接受下线消息

下线消息的处理在InstanceResource类中

@DELETE
    public Response cancelLease(
            @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
        try {
            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();
            }
        } catch (Throwable e) {
            logger.error("Error (cancel): {} - {}", app.getName(), id, e);
            return Response.serverError().build();
        }

    }
 public boolean cancel(final String appName, final String id,
                          final boolean isReplication) {
        if (super.cancel(appName, id, isReplication)) {
          //往集群同步下线信息
            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;
    }

先看具体的下线逻辑，与租约过期清除的处理逻辑是一致的

   protected boolean internalCancel(String appName, String id, boolean isReplication) {
        try {
            read.lock();
            CANCEL.increment(isReplication);
            Map<String, Lease<InstanceInfo>> gMap = registry.get(appName);
            Lease<InstanceInfo> leaseToCancel = null;
            if (gMap != null) {
              //删除租约信息
                leaseToCancel = gMap.remove(id);
            }
            synchronized (recentCanceledQueue) {
                recentCanceledQueue.add(new Pair<Long, String>(System.currentTimeMillis(), appName + "(" + id + ")"));
            }
          //删除客户端状态信息
            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) {
                CANCEL_NOT_FOUND.increment(isReplication);
                logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
                return false;
            } else {
                leaseToCancel.cancel();
                InstanceInfo instanceInfo = leaseToCancel.getHolder();
                String vip = null;
                String svip = null;
                if (instanceInfo != null) {
                    instanceInfo.setActionType(ActionType.DELETED);
                    recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
                    instanceInfo.setLastUpdatedTimestamp();
                    vip = instanceInfo.getVIPAddress();
                    svip = instanceInfo.getSecureVipAddress();
                }
                invalidateCache(appName, vip, svip);
                logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
                return true;
            }
        } finally {
            read.unlock();
        }
    }

其中invalidateCache则是删除当前服务中与该实例相关的缓存

集群的同步下线信息则跟集群信息注册的逻辑差不多

原文地址