Spring Cloud Eureka源码解析之服务下线（六）

比眉伴天荒 2022-09-16 04:56 196阅读 0赞

当Eureka Client 服务关闭停止时，会触发 DiscoveryClient的shutdown关闭eureka-client（**正常关闭，非宕机等的非正常关闭**）

@PreDestroy
    @Override
    public synchronized void shutdown() { 
        if (isShutdown.compareAndSet(false, true)) { 
            logger.info("Shutting down DiscoveryClient ...");
    
            // 关闭状态变更监听器
            if (statusChangeListener != null && applicationInfoManager != null) { 
                applicationInfoManager.unregisterStatusChangeListener(statusChangeListener.getId());
            }
    
            // 关闭该客户端上的定时任务
            cancelScheduledTasks();
    
            // 向server发送下线请求
            if (applicationInfoManager != null
                && clientConfig.shouldRegisterWithEureka()
                && clientConfig.shouldUnregisterOnShutdown()) { 
                applicationInfoManager.setInstanceStatus(InstanceStatus.DOWN);
                unregister();
            }
    
            // 关闭一些资源
            if (eurekaTransport != null) { 
                eurekaTransport.shutdown();
            }
    
            heartbeatStalenessMonitor.shutdown();
            registryStalenessMonitor.shutdown();
    
            logger.info("Completed shut down of DiscoveryClient");
        }
    }

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);
            }
        }
    }

主要看下server如何下线实例

**Eureka Server接收下线请求**

处理下线请求的是InstanceResource\#cancelLease方法  
![在这里插入图片描述][2a4f63beae5ccfc33d110d2dcf08a852.png_pic_center]  
![在这里插入图片描述][07e89166300f8926d93b617008c3e6da.png_pic_center]

@Override
    public boolean cancel(final String appName, final String id,
                          final boolean isReplication) { 
        // 下线
        if (super.cancel(appName, id, isReplication)) { 
            // 下线成功则同步给集群中的其它节点
            replicateToPeers(Action.Cancel, appName, id, null, null, isReplication);
            synchronized (lock) { 
                // 跟注册时一样，重新计算expectedNumberOfRenewsPerMin和numberOfRenewsPerMinThreshold
                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;
    }

@Override
    public boolean cancel(String appName, String id, boolean isReplication) { 
        return internalCancel(appName, id, isReplication);
    }
    
    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) { 
                // 移除该实例的注册租约信息
                leaseToCancel = gMap.remove(id);
            }
            // 添加到最近下线队列中
            synchronized (recentCanceledQueue) { 
                recentCanceledQueue.add(new Pair<Long, String>(System.currentTimeMillis(), appName + "(" + id + ")"));
            }
            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) { 
                // 没有该实例的租约信息，则直接返回false，表示下线失败
                CANCEL_NOT_FOUND.increment(isReplication);
                logger.warn("DS: Registry: cancel failed because Lease is not registered for: {}/{}", appName, id);
                return false;
            } else { 
                // 设置下线时间
                leaseToCancel.cancel();
                InstanceInfo instanceInfo = leaseToCancel.getHolder();
                String vip = null;
                String svip = null;
                if (instanceInfo != null) { 
                    // 添加到最近变更记录队列，ActionType为DELETED，用于增量拉取
                    instanceInfo.setActionType(ActionType.DELETED);
                    recentlyChangedQueue.add(new RecentlyChangedItem(leaseToCancel));
                    instanceInfo.setLastUpdatedTimestamp();
                    vip = instanceInfo.getVIPAddress();
                    svip = instanceInfo.getSecureVipAddress();
                }
                // 使缓存失效，跟注册时一样
                invalidateCache(appName, vip, svip);
                logger.info("Cancelled instance {}/{} (replication={})", appName, id, isReplication);
                return true;
            }
        } finally { 
            read.unlock();
        }
    }

下线的逻辑比较简单

[2a4f63beae5ccfc33d110d2dcf08a852.png_pic_center]: /images/20220828/3e389d3e7709445e90169f5fc5729b0b.png
[07e89166300f8926d93b617008c3e6da.png_pic_center]: /images/20220828/cd165f68f4834f0ca2121c4a5c302b66.png