先说CloudFoundry的命令行工具CLI。我们在CloudFoundry环境下工作，第一个使用的命令就是cf login。
如果在环境变量里维护CF_TRACE的值为true：
则我们能发现，诸如cf login这种命令，实际上也是通过消费Restful API来完成的。
下图是cf login这个命令的api endpoint请求细节，供大家参考：
API endpoint: https://api.cf.eu10.hana.ondemand.com
REQUEST: [2018-09-21T14:50:57+08:00]
GET /v2/info HTTP/1.1
Host: api.cf.eu10.hana.ondemand.com
Accept: application/json
Content-Type: application/json
User-Agent: go-cli 6.36.1+e3799ad7e.2018-04-04 / windows
RESPONSE: [2018-09-21T14:50:59+08:00]
HTTP/1.1 200 OK
Connection: close
Content-Length: 550
Content-Type: application/json;charset=utf-8
Date: Fri, 21 Sep 2018 06:50:58 GMT
Server: nginx
X-Content-Type-Options: nosniff
X-Vcap-Request-Id: abf32f52-294a-41f5-5919-be948d78f0dd::a32b17bb-da82-4d45-930f-f0344c8a83b3
{"name":"","build":"","support":"","version":0,"description":"Cloud Foundry at SAP Cloud Platform","authorization_endpoint":"https://login.cf.eu10.hana.ondemand.com","token_endpoint":"[PRIVATE DATA HIDDEN]","min_cli_version":null,"min_recommended_cli_version":null,"api_version":"2.115.0","app_ssh_endpoint":"ssh.cf.eu10.hana.ondemand.com:2222","app_ssh_host_key_fingerprint":"f3:12:47:b5:3a:19:6e:6c:4e:9d:90:2e:6f:8e:87:cc","app_ssh_oauth_client":"ssh-proxy","doppler_logging_endpoint":"wss://doppler.cf.eu10.hana.ondemand.com:443"}
REQUEST: [2018-09-21T14:50:59+08:00]
GET /login HTTP/1.1
Host: login.cf.eu10.hana.ondemand.com
Accept: application/json
Content-Type: application/json
User-Agent: go-cli 6.36.1+e3799ad7e.2018-04-04 / windows
API响应结果：
RESPONSE: [2018-09-21T14:51:00+08:00]
HTTP/1.1 200 OK
Connection: close
Content-Length: 551
Cache-Control: no-store
Content-Language: en-US
Content-Type: application/json;charset=UTF-8
Date: Fri, 21 Sep 2018 06:50:59 GMT
Set-Cookie: X-Uaa-Csrf=8uoxBvyG8QCwo29efrrZNh; Max-Age=86400; Expires=Sat, 22-Sep-2018 06:51:00 GMT; Path=/; Secure; HttpOnly
Strict-Transport-Security: max-age=31536000 ; includeSubDomains
X-Content-Type-Options: nosniff
X-Frame-Options: DENY
X-Vcap-Request-Id: f6b29d8f-f78e-4c5e-61f3-5c9d906828ed
X-Xss-Protection: 1; mode=block
{"app":{"version":"4.19.0"},"links":{"uaa":"https://uaa.cf.eu10.hana.ondemand.com","passwd":"https://accounts.sap.com/ui/createForgottenPasswordMail?spName=cf.eu10.hana.ondemand.com","login":"https://login.cf.eu10.hana.ondemand.com","register":"https://accounts.sap.com/ui/public/showRegisterForm?spName=cf.eu10.hana.ondemand.com"},"zone_name":"uaa","entityID":"login.cf.eu10.hana.ondemand.com","commit_id":"7897100","idpDefinitions":{},"prompts":{"username":["text","Email"],"password":["password","Password"]},"timestamp":"2018-06-13T12:02:09-0700"}
Email>
再看Kubernetes。我们用的很多的命令：
kubectl get pods，返回pods列表。
而用命令行
kubectl --v=8 get pods
则发现，get pods这个命令实际上也是发请求发往Kubernetes的API server：
https://:6443/api/v1/namespaces/default/pods?limit=500
API请求明细如下：
API server是Kubernetes最重要的核心组件之一：
1. 提供集群管理的REST API接口，包括认证授权、数据校验以及集群状态变更等
2. 提供其他模块之间的数据交互和通信的枢纽（其他模块通过API Server查询或修改
数据，只有API Server才直接操作etcd）
kube-apiserver支持同时提供https（默认监听在6443端口）和http API（默认监听在
127.0.0.1的8080端口），其中http API是非安全接口，不做任何认证授权机制，不建议
生产环境启用。两个接口提供的REST API格式相同，参考Kubernetes API Reference查
看所有API的调用格式。
在实际使用中，通常通过kubectl来访问apiserver，也可以通过Kubernetes各个语言的
client库来访问apiserver。
比如上面get pods命令对应的API的文档：
https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.10/#list-62
