SpringCloud使用Consul时，服务注销的操作方式

1、为什么要服务注销

当服务升级上线时，为了平滑过渡，一般会先把老的服务从注册中心上摘除（服务本身不停止），等该服务完全没有流量时，再进行下线的操作。采用SpringCloudConsul时，内部默认每3s和注册中心同步一次心跳，并以此刷新各个服务的ip列表。当某个服务从注册中心注销时，不需要进行广播，由心跳机制保证该注册中心剩余的所有服务能够感知到。

2、SpringCloudConsul提供的方法

SpringCloudConsul提供了一个ConsulAutoServiceRegistration类，该类主要提供服务的注册和注销功能，源码如下：

/*
 * Copyright 2013-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.cloud.consul.serviceregistry;

import 
import 
import org.springframework.boot.web.context.WebServerInitializedEvent;
import org.springframework.cloud.client.serviceregistry.AbstractAutoServiceRegistration;
import org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationProperties;
import org.springframework.cloud.consul.discovery.ConsulDiscoveryProperties;
import org.springframework.retry.annotation.Retryable;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

/**
 * @author Spencer Gibb
 */
public class ConsulAutoServiceRegistration extends AbstractAutoServiceRegistration<ConsulRegistration> {

    private static Log log = LogFactory.getLog(ConsulAutoServiceRegistration.class);

    private ConsulDiscoveryProperties properties;
    private ConsulAutoRegistration registration;

    public ConsulAutoServiceRegistration(ConsulServiceRegistry serviceRegistry,
            AutoServiceRegistrationProperties autoServiceRegistrationProperties,
            ConsulDiscoveryProperties properties, ConsulAutoRegistration registration) {
        super(serviceRegistry, autoServiceRegistrationProperties);
        this.properties = properties;
        this.registration = registration;
    }

    void setPortIfNeeded(int port) {
         port);
    }

    @Override
    protected ConsulAutoRegistration getRegistration() {
        if (this.registration.getService().getPort() == null && this.getPort().get() > 0) {
            this.registration.initializePort(this.getPort().get());
        }
        Assert.notNull(this.registration.getService().getPort(), "service.port has not been set");
        return this.registration;
    }

    @Override
    protected ConsulAutoRegistration getManagementRegistration() {
        return this.registration.managementRegistration();
    }

    @Override
    @Retryable(interceptor = "consulRetryInterceptor")
    public void start() {
        super.start();
    }

    @Override
    protected void register() {
        if (!this.properties.isRegister()) {
            log.debug("Registration disabled.");
            return;
        }

        super.register();
    }

    @Override
    protected void registerManagement() {
        if (!this.properties.isRegister()) {
            return;
        }
        super.registerManagement();

    }

    @Override
    protected Object getConfiguration() {
        return properties;
    }

    @Override
    protected void deregister() {
        if (!this.properties.isRegister() || !this.properties.isDeregister()) {
            return;
        }
        super.deregister();
    }

    @Override
    protected void deregisterManagement() {
        if (!this.properties.isRegister() || !this.properties.isDeregister()) {
            return;
        }
        super.deregisterManagement();
    }

    @Override
    protected boolean isEnabled() {
        return this.properties.getLifecycle().isEnabled();
    }

    @Override
    @SuppressWarnings("deprecation")
    protected String getAppName() {
        String appName = properties.getServiceName();
        return StringUtils.isEmpty(appName) ? super.getAppName() : appName;
    }

    @Override
    public void bind(WebServerInitializedEvent event) {
        // do nothing so we can listen for this event in a different class
        // this ensures start() can be retried if spring-retry is available
    }
}

其中服务注销的方法逻辑是：

image-20190218160430479

该方法会最终是调用consul提供的restfulAPI去进行服务的注销：

image-20190218160611472

3、测试SpringCloudConsul的注销方法

我们写一段代码进行服务注销的测试：

@RestController
public class ConsulController {

    private final ConsulAutoServiceRegistration serviceRegistration;

    public ConsulController(ConsulAutoServiceRegistration serviceRegistration) {
        this.serviceRegistration = serviceRegistration;
    }

    @DeleteMapping("deregister")
    public void deregister() {
        serviceRegistration.stop();
    }
    
}

服务启动后consul界面显示服务状态为绿色，代表正常：

image-20190218160840196

执行该接口后，正常情况下consul会摘除这个服务的注册信息，但是多试验几次后，会发现服务信息还在，这个时候如果服务停止的话，必然会出现调用异常的情况，consul上的服务状态为橙色:

image-20190218161830400 image-20190218162026267

4、完整的注销操作

显然以上的做法并不能真正的完成服务注销的操作，consul的注销操作需要到集群中的节点上才能完成，具体代码如下：

@RestController
@Slf4j
public class ConsulController {

    private final ConsulClient consulClient;
    private final ConsulRegistration consulRegistration;

    public ConsulController(ConsulClient consulClient, ConsulRegistration consulRegistration) {
        this.consulClient = consulClient;
        this.consulRegistration = consulRegistration;
    }

    @DeleteMapping("api/deregister")
    public void deregister() {
        String currentInstanceId = consulRegistration.getInstanceId();
        List<Member> members = consulClient.getAgentMembers().getValue();
        for (Member member : members) {
            String address = member.getAddress();
            ConsulClient clearClient = new ConsulClient(address);
            try {
                Map<String, Service> serviceMap = clearClient.getAgentServices().getValue();
                for (Entry<String, Service> entry : serviceMap.entrySet()) {
                    Service service = entry.getValue();
                    String instanceId = service.getId();
                    if (currentInstanceId.equals(instanceId)) {
                        log.warn("在{}客户端上的服务 :{}为无效服务，准备清理...................", address, currentInstanceId);
                        clearClient.agentServiceDeregister(currentInstanceId);
                    }
                }
            } catch (Exception e) {
                log.error("异常信息: {}", e);
            }
        }
    }

}

5、如何让服务在consul上进入维护模式（临时摘除）

暴露/service-registry 端点（需要引入spring-boot-starter-actuator支持）
SpringCloudConsul提供【上线】和【离线】两种服务状态的设置，具体代码在ConsulServiceRegistry类中
image-20190218164331970

发送POST请求到/actuator/service-registry 端点，此时状态应为OUT_OF_SERVICE

curl -X "POST" "http://localhost:8081/actuator/service-registry?status=OUT_OF_SERVICE" -H "Content-Type: application/vnd.spring-boot.actuator.v2+json;charset=UTF-8"

此时consul中显示服务状态进入维护模式：
image-20190218164643941

恢复操作时，只需要将状态变更为UP即可，执行完毕后consul上的服务状态恢复：

curl -X "POST" "http://localhost:8081/actuator/service-registry?status=UP" -H "Content-Type: application/vnd.spring-boot.actuator.v2+json;charset=UTF-8"