在《你好spring-cloud-kubernetes》一文中,对spring-cloud-kubernetes这个SpringCloud官方kubernetes服务框架有了基本了解,今天来小结此框架涉及的关键技术,为后面的深入学习做准备;
本文是《spring-cloud-kubernetes实战系列》的第三篇,全文链接如下:
总结下来有三个关键知识点需要深入理解:
接下来我们逐一分析每个知识点;
先来回顾一下上一章的DiscoveryController.java的内容:
@RestController
public class DiscoveryController {
@Autowired
private DiscoveryClient discoveryClient;
/**
* 探针检查响应类
* @return
*/
@RequestMapping("/health")
public String health() {
return "health";
}
/**
* 返回远程调用的结果
* @return
*/
@RequestMapping("/getservicedetail")
public String getUri(
@RequestParam(value = "servicename", defaultValue = "") String servicename) {
return "Service [" + servicename + "]'s instance list : " + JSON.toJSONString(discoveryClient.getInstances(servicename));
}
/**
* 返回发现的所有服务
* @return
*/
@RequestMapping("/services")
public String services() {
return this.discoveryClient.getServices().toString()
+ ", "
+ new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
}
}
上述代码中,我们并没有写创建DiscoveryClient实例的代码,discoveryClient从何而来?
这一切,要从DiscoveryController.java所在项目的pom.xml说起;
<dependency>
<groupId>org.springframework.cloudgroupId>
<artifactId>spring-cloud-kubernetes-discoveryartifactId>
<version>1.0.1.RELEASEversion>
dependency>
/**
* Bootstrap config for Kubernetes discovery config client.
*
* @author Zhanwei Wang
*/
@Configuration
@ConditionalOnProperty("spring.cloud.config.discovery.enabled")
@Import({ KubernetesAutoConfiguration.class,
KubernetesDiscoveryClientAutoConfiguration.class })
public class KubernetesDiscoveryClientConfigClientBootstrapConfiguration {
}
@Bean
@ConditionalOnMissingBean
public KubernetesClient kubernetesClient(Config config) {
return new DefaultKubernetesClient(config);
}
@Bean
@ConditionalOnMissingBean
@ConditionalOnProperty(name = "spring.cloud.kubernetes.discovery.enabled", matchIfMissing = true)
public KubernetesDiscoveryClient kubernetesDiscoveryClient(KubernetesClient client,
KubernetesDiscoveryProperties properties,
KubernetesClientServicesFunction kubernetesClientServicesFunction,
DefaultIsServicePortSecureResolver isServicePortSecureResolver) {
return new KubernetesDiscoveryClient(client, properties,
kubernetesClientServicesFunction, isServicePortSecureResolver);
}
接下来看第二个问题;
@RequestMapping("/services")
public String services() {
return this.discoveryClient.getServices().toString()
+ ", "
+ new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
}
如上所示,discoveryClient.getServices()方法返回了所有kubernetes的服务信息;
2. discoveryClient对应的类是spring-cloud-kubernetes项目的KubernetesDiscoveryClient.java,看方法:
public List<String> getServices(Predicate<Service> filter) {
return this.kubernetesClientServicesFunction.apply(this.client).list().getItems()
.stream().filter(filter).map(s -> s.getMetadata().getName())
.collect(Collectors.toList());
}
这段代码的关键在于this.kubernetesClientServicesFunction.apply(this.client).list(),先看KubernetesClientServicesFunction实例的初始化过程,在KubernetesDiscoveryClientAutoConfiguration类中:
@Bean
public KubernetesClientServicesFunction servicesFunction(
KubernetesDiscoveryProperties properties) {
if (properties.getServiceLabels().isEmpty()) {
return KubernetesClient::services;
}
return (client) -> client.services().withLabels(properties.getServiceLabels());
}
KubernetesClientServicesFunction是个lambda表达式,用于KubernetesClient的时候,返回KubernetesClient.services()的结果,如果指定了标签过滤,就用指定的标签来做过滤(也就是kubernetes中的标签选择器的效果)
因此,数据来源其实就是上面的this.client,调用其services方法的返回结果;
3. KubernetesDiscoveryClient.getServices方法中的this.client是什么呢?分析前面的问题时已经提到过了,就是DefaultKubernetesClient类的实例,所以,此时要去看DefaultKubernetesClient.services方法,发现client是ServiceOperationsImpl实例:
@Override
public MixedOperation<Service, ServiceList, DoneableService, ServiceResource<Service, DoneableService>> services() {
return new ServiceOperationsImpl(httpClient, getConfiguration(), getNamespace());
}
public L list() throws KubernetesClientException {
try {
HttpUrl.Builder requestUrlBuilder = HttpUrl.get(getNamespacedUrl()).newBuilder();
String labelQueryParam = getLabelQueryParam();
if (Utils.isNotNullOrEmpty(labelQueryParam)) {
requestUrlBuilder.addQueryParameter("labelSelector", labelQueryParam);
}
String fieldQueryString = getFieldQueryParam();
if (Utils.isNotNullOrEmpty(fieldQueryString)) {
requestUrlBuilder.addQueryParameter("fieldSelector", fieldQueryString);
}
Request.Builder requestBuilder = new Request.Builder().get().url(requestUrlBuilder.build());
L answer = handleResponse(requestBuilder, listType);
updateApiVersion(answer);
return answer;
} catch (InterruptedException | ExecutionException | IOException e) {
throw KubernetesClientException.launderThrowable(forOperationType("list"), e);
}
}
展开上面代码的handleResponse方法,可见里面是一次http请求,至于请求的地址,可以展开getNamespacedUrl()方法,里面调用的getRootUrl方法如下:
public URL getRootUrl() {
try {
if (apiGroup != null) {
return new URL(URLUtils.join(config.getMasterUrl().toString(), "apis", apiGroup, apiVersion));
}
return new URL(URLUtils.join(config.getMasterUrl().toString(), "api", apiVersion));
} catch (MalformedURLException e) {
throw KubernetesClientException.launderThrowable(e);
}
}
可见最终的地址应该是:xxxxxx/api/v1或者xxxxxx/apis/xx/v1这样的字符串。
这样的字符串意味着什么呢?这是访问kubernetes的API Server时用到的URL标准格式,有关API Server服务的详情请参考官方文档,地址是:https://kubernetes.io/docs/reference/using-api/api-concepts/
如下图,用OperationSupport类的源码和官方文档的URL截图做个对比,大家就一目了然了:
5. 还剩个小问题,上图中,OperationSupport类的成员变量resourceT是什么值?官方文档示例中是"pods",在获取service的时候又该是多少呢?顺着源码一路找下去,找到了类的构造方法,如下所示,第五个参数就是resourceT,这里直接被写死为"services":
public ServiceOperationsImpl(OkHttpClient client, Config config, String apiVersion, String namespace, String name, Boolean cascading, Service item, String resourceVersion, Boolean reloadingFromServer, long gracePeriodSeconds, Map<String, String> labels, Map<String, String> labelsNot, Map<String, String[]> labelsIn, Map<String, String[]> labelsNotIn, Map<String, String> fields) {
super(client, config, null, apiVersion, "services", namespace, name, cascading, item, resourceVersion, reloadingFromServer, gracePeriodSeconds, labels, labelsNot, labelsIn, labelsNotIn, fields);
}
至此,第二个问题“controller中用到的kubernetes服务数据从何而来"已经清楚了:最终是调用okhttp的newCall方法向kubernetes的API Server发起http请求,获取service资源的数据列表;
接下来,该最后一个问题了;
关于API Server如何响应各类http请求,本文只做一些简单的说明,详细信息还请参考官方文档,地址是:https://kubernetes.io/docs/reference/command-line-tools-reference/kube-apiserver/
如下图所示,在kubernetes环境中,pod、service这些资源的数据都存储在etcd,任何服务想要增删改查etcd的数据,都只能通过向API Server发起RestFul请求的方式来完成,咱们的DiscoveryController类获取所有service也是发请求到API Server,由API Server从etcd中取得service的数据返回给DiscoveryController:
如果您想弄清楚service数据在etcd中如何存储的,可以参考《查看k8s的etcd数据》一文,亲自动手连接etcd查看里面的service内容;
至此,spring-cloud-kubernetes背后的三个关键知识点都已经学习了,下图算是对这些问题的一个小结:
希望以上的分析总结能对您有参考作用,由于对基本原理都已经了解,后面的spring-cloud-kubernetes实战可以更顺畅,也能从原理出发继续深入的分析和学习。