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
2.1 基于httpClient设计ServiceCenter客户端
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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); } -
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(); }
2.2 ServiceCenter客户端核心API
- 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); } } - 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); } }
2.3 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
3.1 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
3.2 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 !”。
3.3 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。
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