使用ServiceComb客户端轻松调用ServiceCenter

使用ServiceComb客户端轻松调用ServiceCenter

1. 问题/背景

在微服务架构中，服务注册中心是必不可少的组件，提供服务注册与管理的能力。目前使用ServiceComb服用中心的java微服务开发者，不仅需要写微服务业务代码，还要写客户端代码去调用ServiceCenter的openAPI。开发者首先需要熟悉ServiceCenter的openAPI文档，然后代码实现http客户端用于发起请求和接收响应，并绑定ServiceCenter配置参数，最后代码实现对服务中心API的调用，才能使用上ServiceCenter。为了简单化开发者使用ServiceCenter，ServiceCenter客户端实现了上述步骤。开发者只需要添加客户端jar包调用API就能轻松使用ServiceCenter，不需要过多关注openAPI文档、不需要写http客户端层代码。使用ServiceComb客户端，开发者可以轻松调用ServiceCenter，更专注于写微服务业务代码。
了解更多ServiceComb-Service-Center：https://docs.servicecomb.io/service-center/zh_CN/index.html
了解更多ServiceCenter客户端：https://github.com/apache/servicecomb-java-chassis/tree/master/clients/service-center-client

2. 客户端原理及关键代码解读

• 基于httpClient设计ServiceCenter客户端

1. 客户端发起请求和接收响应。客户端选择httpclient作为底层组件，用于实际发起请求和接收响应，并对请求和响应类进行了封装。代码中get方法对应发起GET请求，调用doRequest方法首先添加服务注册中心信息到封装过的httpRequest请求头部，再基于httpclient组件发起实际的http请求，最后将请求响应结果转化为封装过的httpResponse对象返回。

   //make GET request
   @Override
   public HttpResponse get(HttpRequest request) throws IOException {
       request.setMethod(HttpRequest.GET);
       return doRequest(request);
   }
   ......
   
   //make http request with httpClient component
   public HttpResponse doRequest(HttpRequest httpRequest) throws IOException {
       //add cse-serviceregistry-client header to identify client
       httpRequest.addHeader(HEADER_CONTENT_TYPE, "application/json");
       httpRequest.addHeader(HEADER_USER_AGENT, "cse-serviceregistry-client/1.0.0");
       
       if (globalHeaders != null) {
       globalHeaders.forEach(httpRequest::addHeader);
       }
       
       //make http request
       org.apache.http.HttpResponse response = httpClient.execute(httpRequest.getRealRequest());
       
       int statusCode = response.getStatusLine().getStatusCode();
       String messgae = response.getStatusLine().getReasonPhrase();
       String context = EntityUtils.toString(response.getEntity(), "UTF-8");
       
       return new HttpResponse(statusCode, messgae, context);
   }
   

2. 客户端支持定制化服务中心配置参数。代码中看到，客户端支持开发者定制服务中心IP，端口，项目名称，租户名称，导入TLSConfig和新增请求头，并通过客户端的Builder方法注入配置。TLSConfig为客户端TLS认证配置类，给客户端导入TLS证书配置，即可开启客户端双向认证模式。

   /**
   * Customized host, port, projectName, tenantName, TLSConf, headers and any one parameter can be null.
   */
   public ServiceCenterClient(String host, int port, String projectName, String tenantName, TLSConfig tlsConfig,
     Map<String, String> extraGlobalHeaders) {
   HttpTransport httpTransport = HttpTransportFactory.getDefaultHttpTransport();
   if (tlsConfig != null) {
     httpTransport = new TLSHttpsTransport(tlsConfig);
   }
   httpTransport.addHeaders(extraGlobalHeaders);
   
   //set configuration parameters
   this.httpClient = new ServiceCenterRawClient.Builder()
       .setHost(host)
       .setPort(port)
       .setProjectName(projectName)
       .setTenantName(tenantName)
       .setHttpTransport(httpTransport).build();
   }
   

• ServiceCenter客户端核心API

1. 服务注册与发现，注册服务和实例到服务注册中心，根据服务ID发现服务实例。registerMicroserviceInstance方法用于注册服务实例，发起httpPOST请求访问服务实例注册URL，并将实例注入到请求body中，返回服务ID字符串; getMicroserviceInstanceList方法用于发现服务的所有实例，根据服务ID，发起httpGET请求访问服务发现URL，返回MicroserviceInstancesResponse对象。

   //service register
   public String registerMicroserviceInstance(MicroserviceInstance instance, String serviceId) {
       try {
         ObjectMapper mapper = new ObjectMapper();
         mapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
         HttpResponse response = httpClient.postHttpRequest("/registry/microservices/" + serviceId + "/instances", null,
             mapper.writeValueAsString(instance));
         if (response.getStatusCode() == HttpStatus.SC_OK) {
           return response.getContent();
         } else {
           throw new OperationException(
               "register service instance fails, statusCode = " + response.getStatusCode() + "; message = " + response
                   .getMessage()
                   + "; content = " + response.getContent());
         }
       } catch (IOException e) {
         throw new OperationException(
             "register service instance fails", e);
       }
   }
   //service discovery
   public MicroserviceInstancesResponse getMicroserviceInstanceList(String serviceId) {
       try {
         HttpResponse response = httpClient
             .getHttpRequest("/registry/microservices/" + serviceId + "/instances", null, null);
         if (response.getStatusCode() == HttpStatus.SC_OK) {
           ObjectMapper mapper = new ObjectMapper();
           return mapper.readValue(response.getContent(), MicroserviceInstancesResponse.class);
         } else {
           throw new OperationException(
               "get service instances list fails, statusCode = " + response.getStatusCode() + "; message = " + response
                   .getMessage()
                   + "; content = " + response.getContent());
         }
       } catch (IOException e) {
         throw new OperationException(
             "get service instances list fails", e);
       }
   }      
   

2. 心跳，服务实例发送心跳告知服务中心。代码中发起httpPUT请求中访问心跳URL，并导入HeartbeatsRequest （包含服务ID和实例ID）到请求body中，响应状态码为200表示心跳成功。

   //heartBeats
   public void sendHeartBeats(HeartbeatsRequest heartbeatsRequest) {
     try {
       ObjectMapper mapper = new ObjectMapper();
       HttpResponse response = httpClient
           .putHttpRequest("/registry/heartbeats", null, mapper.writeValueAsString(heartbeatsRequest));
   
       if (response.getStatusCode() == HttpStatus.SC_OK) {
         LOGGER.info("HEARTBEATS SUCCESS");
       } else {
         throw new OperationException(
             "heartbeats fails, statusCode = " + response.getStatusCode() + "; message = " + response.getMessage()
                 + "; content = " + response.getContent());
       }
     } catch (IOException e) {
       throw new OperationException(
           "heartbeats fails ", e);
     }
   }
   

3. 更多客户端API介绍，参考客户端说明文档 https://github.com/apache/servicecomb-java-chassis/tree/master/clients/service-center-client

3. ServiceCenter客户端实践

1. 实践准备
   • 启动ServiceComb服务中心：http://servicecomb.apache.org/cn/docs/service-center/install/
   • 下载演示代码：https://github.com/zaneChou1/spring-boot-servicecenter
2. provider端启动服务，通过客户端注册到ServiceCenter
   运行provider模块，启动helloServer服务，并调用客户端API创建客户端对象、创建helloServer服务和实例对象、注册服务和实例到servicecomb 服务中心，并保持30s一次心跳，代码实现如下。

    public static void registerMicroservice(){
    	//new ServiceCenterClient object
   	 ServiceCenterClient sc = new ServiceCenterClient();
   	
   	 //new Microservice object and setting properties and serviceName is necessary
   	 Microservice microservice = new Microservice();
   	 microservice.setServiceId("1111");
   	 microservice.setServiceName("HelloServer");
   	 //register microservice to service-center
   	 sc.registerMicroservice(microservice);
   	
   	 //new MicroserviceInstance object and bind server IP and port
   	 MicroserviceInstance instance = new MicroserviceInstance();
   	 List<String> endPoints = new ArrayList<String>();
   	 endPoints.add("rest://127.0.0.1:8080/");
   	 instance.setEndpoints(endPoints);
   	 //setting instance hostName, instanceId and hostName is necessary
   	 instance.setHostName("test");
   	 instance.setInstanceId("2222");
   	 //register microservice instance to service-center
   	 sc.registerMicroserviceInstance(instance,microservice.getServiceId());
   	
   	 //send a heartbeat every 30s
   	 HeartbeatsRequest heartbeatsRequest = new HeartbeatsRequest("1111","2222");
   	 while(true){
   	   sc.sendHeartBeats(heartbeatsRequest);
   	   try {
   	     Thread.sleep(30000);
   	   } catch (InterruptedException e) {
   	     e.printStackTrace();
   	   }
   	 }
   }
   

   查看service-center的UI显示如下，helloServer服务注册到服务中心成功，且有一个服务实例test。
   
   访问provider服务监听的8080端口，返回“Hello Spring-Boot-ServiceCenter !”。
   
3. consumer端通过客户端发现服务实例，发起服务调用
   运行consumer模块，启动consumer服务，调用客户端API新建客户端对象、发现helloServer服务实例、获取服务监听的IP和端口，最后调用provider端helloServer服务返回结果。

   //find service instance
   ServiceCenterClient sc = new ServiceCenterClient();
   MicroserviceInstancesResponse instances = sc.getMicroserviceInstanceList("1111");
   //get IP and port that service is listening on
   URI endpointURIBuilder = new URIBuilder(instances.getInstances().get(0).getEndpoints().get(0)).build();
   int port = endpointURIBuilder.getPort();
   String host = endpointURIBuilder.getHost();
   
   //call service
   RestTemplate restTemplate = new RestTemplate();
   ResponseEntity<String> result = restTemplate.getForEntity("http://"+host+":"+port,String.class);
   return result.getBody();
   

   访问consumer端监听的8081端口，返回helloServer的响应结果“Hello Spring-Boot-ServiceCenter !”，consumer端通过ServiceComb服务注册中心调用provider端服务成功。