这篇文章将为大家详细讲解有关kubernetes API Server原理分析是怎样的，文章内容质量较高，因此小编分享给大家做个参考，希望大家阅读完这篇文章后对相关知识有一定的了解。

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一：简介
k8s API Server提供了k8s各类资源对象（pod,RC,Service等）的增删改查及watch等HTTP Rest接口，是整个系统的数据总线和数据中心。功能特性：
1.是集群管理的API入口
2.是资源配额控制的入口
3.提供了完善的集群安全机制


二：概述
通常可以通过命令行工具Kubectl来与API Server交互，它们之间的接口是REST调用，同时也可以使用curl命令行工具进行快速验证。通过配置参数KUBE_MASTER="--master=http://10.116.137.196:8080" 客户获得API Server的访问路径。

1.获取 API的版本信息
curl 10.116.137.196:8080/api

点击(此处)折叠或打开

1. {

2.   "kind": "APIVersions",

3.   "versions": [

4.     "v1"

5.   ],

6.   "serverAddressByClientCIDRs": [

7.     {

8.       "clientCIDR": "0.0.0.0/0",

9.       "serverAddress": "10.116.137.196:6443"

10.     }

11.   ]

12. }

2.获取目前所支持的资源对象的种类
curl 10.116.137.196:8080/api/v1

1. {

2.   "kind": "APIResourceList",

3.   "groupVersion": "v1",

4.   "resources": [

5.     {

6.       "name": "bindings",

7.       "singularName": "",

8.       "namespaced": true,

9.       "kind": "Binding",

10.       "verbs": [

11.         "create"

12.       ]

13.     },

14.     {

15.       "name": "componentstatuses",

16.       "singularName": "",

17.       "namespaced": false,

18.       "kind": "ComponentStatus",

19.       "verbs": [

20.         "get",

21.         "list"

22.       ],

23.       "shortNames": [

24.         "cs"

25.       ]

26.     },

27.     {

28.       "name": "configmaps",

29.       "singularName": "",

30.       "namespaced": true,

31.       "kind": "ConfigMap",

32.       "verbs": [

33.         "create",

34.         "delete",

35.         "deletecollection",

36.         "get",

37.         "list",

38.         "patch",

39.         "update",

40.         "watch"

41.       ],

42.       "shortNames": [

43.         "cm"

44.       ]

45.     },

46.     {

47.       "name": "endpoints",

48.       "singularName": "",

49.       "namespaced": true,

50.       "kind": "Endpoints",

51.       "verbs": [

52.         "create",

53.         "delete",

54.         "deletecollection",

55.         "get",

56.         "list",

57.         "patch",

58.         "update",

59.         "watch"

60.       ],

61.       "shortNames": [

62.         "ep"

63.       ]

64.     },

65.     {

66.       "name": "events",

67.       "singularName": "",

68.       "namespaced": true,

69.       "kind": "Event",

70.       "verbs": [

71.         "create",

72.         "delete",

73.         "deletecollection",

74.         "get",

75.         "list",

76.         "patch",

77.         "update",

78.         "watch"

79.       ],

80.       "shortNames": [

81.         "ev"

82.       ]

83.     },

84.     {

85.       "name": "limitranges",

86.       "singularName": "",

87.       "namespaced": true,

88.       "kind": "LimitRange",

89.       "verbs": [

90.         "create",

91.         "delete",

92.         "deletecollection",

93.         "get",

94.         "list",

95.         "patch",

96.         "update",

97.         "watch"

98.       ],

99.       "shortNames": [

100.         "limits"

101.       ]

102.     },

103.     {

104.       "name": "namespaces",

105.       "singularName": "",

106.       "namespaced": false,

107.       "kind": "Namespace",

108.       "verbs": [

109.         "create",

110.         "delete",

111.         "get",

112.         "list",

113.         "patch",

114.         "update",

115.         "watch"

116.       ],

117.       "shortNames": [

118.         "ns"

119.       ]

120.     },

121.     {

122.       "name": "namespaces/finalize",

123.       "singularName": "",

124.       "namespaced": false,

125.       "kind": "Namespace",

126.       "verbs": [

127.         "update"

128.       ]

129.     },

130.     {

131.       "name": "namespaces/status",

132.       "singularName": "",

133.       "namespaced": false,

134.       "kind": "Namespace",

135.       "verbs": [

136.         "get",

137.         "patch",

138.         "update"

139.       ]

140.     },

141.     {

142.       "name": "nodes",

143.       "singularName": "",

144.       "namespaced": false,

145.       "kind": "Node",

146.       "verbs": [

147.         "create",

148.         "delete",

149.         "deletecollection",

150.         "get",

151.         "list",

152.         "patch",

153.         "proxy",

154.         "update",

155.         "watch"

156.       ],

157.       "shortNames": [

158.         "no"

159.       ]

160.     },

161.     {

162.       "name": "nodes/proxy",

163.       "singularName": "",

164.       "namespaced": false,

165.       "kind": "Node",

166.       "verbs": []

167.     },

168.     {

169.       "name": "nodes/status",

170.       "singularName": "",

171.       "namespaced": false,

172.       "kind": "Node",

173.       "verbs": [

174.         "get",

175.         "patch",

176.         "update"

177.       ]

178.     },

179.     {

180.       "name": "persistentvolumeclaims",

181.       "singularName": "",

182.       "namespaced": true,

183.       "kind": "PersistentVolumeClaim",

184.       "verbs": [

185.         "create",

186.         "delete",

187.         "deletecollection",

188.         "get",

189.         "list",

190.         "patch",

191.         "update",

192.         "watch"

193.       ],

194.       "shortNames": [

195.         "pvc"

196.       ]

197.     },

198.     {

199.       "name": "persistentvolumeclaims/status",

200.       "singularName": "",

201.       "namespaced": true,

202.       "kind": "PersistentVolumeClaim",

203.       "verbs": [

204.         "get",

205.         "patch",

206.         "update"

207.       ]

208.     },

209.     {

210.       "name": "persistentvolumes",

211.       "singularName": "",

212.       "namespaced": false,

213.       "kind": "PersistentVolume",

214.       "verbs": [

215.         "create",

216.         "delete",

217.         "deletecollection",

218.         "get",

219.         "list",

220.         "patch",

221.         "update",

222.         "watch"

223.       ],

224.       "shortNames": [

225.         "pv"

226.       ]

227.     },

228.     {

229.       "name": "persistentvolumes/status",

230.       "singularName": "",

231.       "namespaced": false,

232.       "kind": "PersistentVolume",

233.       "verbs": [

234.         "get",

235.         "patch",

236.         "update"

237.       ]

238.     },

239.     {

240.       "name": "pods",

241.       "singularName": "",

242.       "namespaced": true,

243.       "kind": "Pod",

244.       "verbs": [

245.         "create",

246.         "delete",

247.         "deletecollection",

248.         "get",

249.         "list",

250.         "patch",

251.         "proxy",

252.         "update",

253.         "watch"

254.       ],

255.       "shortNames": [

256.         "po"

257.       ],

258.       "categories": [

259.         "all"

260.       ]

261.     },

262.     {

263.       "name": "pods/attach",

264.       "singularName": "",

265.       "namespaced": true,

266.       "kind": "Pod",

267.       "verbs": []

268.     },

269.     {

270.       "name": "pods/binding",

271.       "singularName": "",

272.       "namespaced": true,

273.       "kind": "Binding",

274.       "verbs": [

275.         "create"

276.       ]

277.     },

278.     {

279.       "name": "pods/eviction",

280.       "singularName": "",

281.       "namespaced": true,

282.       "group": "policy",

283.       "version": "v1beta1",

284.       "kind": "Eviction",

285.       "verbs": [

286.         "create"

287.       ]

288.     },

289.     {

290.       "name": "pods/exec",

291.       "singularName": "",

292.       "namespaced": true,

293.       "kind": "Pod",

294.       "verbs": []

295.     },

296.     {

297.       "name": "pods/log",

298.       "singularName": "",

299.       "namespaced": true,

300.       "kind": "Pod",

301.       "verbs": [

302.         "get"

303.       ]

304.     },

305.     {

306.       "name": "pods/portforward",

307.       "singularName": "",

308.       "namespaced": true,

309.       "kind": "Pod",

310.       "verbs": []

311.     },

312.     {

313.       "name": "pods/proxy",

314.       "singularName": "",

315.       "namespaced": true,

316.       "kind": "Pod",

317.       "verbs": []

318.     },

319.     {

320.       "name": "pods/status",

321.       "singularName": "",

322.       "namespaced": true,

323.       "kind": "Pod",

324.       "verbs": [

325.         "get",

326.         "patch",

327.         "update"

328.       ]

329.     },

330.     {

331.       "name": "podtemplates",

332.       "singularName": "",

333.       "namespaced": true,

334.       "kind": "PodTemplate",

335.       "verbs": [

336.         "create",

337.         "delete",

338.         "deletecollection",

339.         "get",

340.         "list",

341.         "patch",

342.         "update",

343.         "watch"

344.       ]

345.     },

346.     {

347.       "name": "replicationcontrollers",

348.       "singularName": "",

349.       "namespaced": true,

350.       "kind": "ReplicationController",

351.       "verbs": [

352.         "create",

353.         "delete",

354.         "deletecollection",

355.         "get",

356.         "list",

357.         "patch",

358.         "update",

359.         "watch"

360.       ],

361.       "shortNames": [

362.         "rc"

363.       ],

364.       "categories": [

365.         "all"

366.       ]

367.     },

368.     {

369.       "name": "replicationcontrollers/scale",

370.       "singularName": "",

371.       "namespaced": true,

372.       "group": "autoscaling",

373.       "version": "v1",

374.       "kind": "Scale",

375.       "verbs": [

376.         "get",

377.         "patch",

378.         "update"

379.       ]

380.     },

381.     {

382.       "name": "replicationcontrollers/status",

383.       "singularName": "",

384.       "namespaced": true,

385.       "kind": "ReplicationController",

386.       "verbs": [

387.         "get",

388.         "patch",

389.         "update"

390.       ]

391.     },

392.     {

393.       "name": "resourcequotas",

394.       "singularName": "",

395.       "namespaced": true,

396.       "kind": "ResourceQuota",

397.       "verbs": [

398.         "create",

399.         "delete",

400.         "deletecollection",

401.         "get",

402.         "list",

403.         "patch",

404.         "update",

405.         "watch"

406.       ],

407.       "shortNames": [

408.         "quota"

409.       ]

410.     },

411.     {

412.       "name": "resourcequotas/status",

413.       "singularName": "",

414.       "namespaced": true,

415.       "kind": "ResourceQuota",

416.       "verbs": [

417.         "get",

418.         "patch",

419.         "update"

420.       ]

421.     },

422.     {

423.       "name": "secrets",

424.       "singularName": "",

425.       "namespaced": true,

426.       "kind": "Secret",

427.       "verbs": [

428.         "create",

429.         "delete",

430.         "deletecollection",

431.         "get",

432.         "list",

433.         "patch",

434.         "update",

435.         "watch"

436.       ]

437.     },

438.     {

439.       "name": "serviceaccounts",

440.       "singularName": "",

441.       "namespaced": true,

442.       "kind": "ServiceAccount",

443.       "verbs": [

444.         "create",

445.         "delete",

446.         "deletecollection",

447.         "get",

448.         "list",

449.         "patch",

450.         "update",

451.         "watch"

452.       ],

453.       "shortNames": [

454.         "sa"

455.       ]

456.     },

457.     {

458.       "name": "services",

459.       "singularName": "",

460.       "namespaced": true,

461.       "kind": "Service",

462.       "verbs": [

463.         "create",

464.         "delete",

465.         "get",

466.         "list",

467.         "patch",

468.         "proxy",

469.         "update",

470.         "watch"

471.       ],

472.       "shortNames": [

473.         "svc"

474.       ],

475.       "categories": [

476.         "all"

477.       ]

478.     },

479.     {

480.       "name": "services/proxy",

481.       "singularName": "",

482.       "namespaced": true,

483.       "kind": "Service",

484.       "verbs": []

485.     },

486.     {

487.       "name": "services/status",

488.       "singularName": "",

489.       "namespaced": true,

490.       "kind": "Service",

491.       "verbs": [

492.         "get",

493.         "patch",

494.         "update"

495.       ]

496.     }

497.   ]

498. }

3.如果只想对外暴露部分REST服务，则可以在Master或其他任何节点上通过运行kubectl proxy进程启动一个内部代理来实现
kubectl proxy --port=8001

三：Kubernetes Proxy API接口

 API Server最主要的REST接口是资源对象的增删改查，另外还有一类特殊的REST接口--Kubernetes  Proxy API接口，这类接口的作用是代理REST请求，即kubernetes API Server把收到的REST请求转发到某个Node上的kubelet守护进程的REST端口上，由该kubelet进程负责响应。

1.Node 相关的接口

点击(此处)折叠或打开

1. /api/v1/proxy/nodes/{name}/pods/    #列出指定节点内所有Pod的信息

3. /api/v1/proxy/nodes/{name}/stats/   #列出指定节点内物理资源的统计信息

5. /api/v1/prxoy/nodes/{name}/spec/    #列出指定节点的概要信息

这里获取的Pod信息来自Node而非etcd数据库，两者时间点可能存在偏差。

2.Pod 相关的接口

点击(此处)折叠或打开

1. /api/v1/proxy/namespaces/{namespace}/pods/{name}/{path:*} #访问pod的某个服务接口

3. /api/v1/proxy/namespaces/{namespace}/pods/{name} #访问Pod

5. #以下写法不同，功能一样

7. /api/v1/namespaces/{namespace}/pods/{name}/proxy/{path:*} #访问pod的某个服务接口

9. /api/v1/namespaces/{namespace}/pods/{name}/proxy               #访问Pod

Pod的proxy接口的作用：在kubernetes集群之外访问某个pod容器的服务（HTTP服务），可以用Proxy API实现，这种场景多用于管理目的，比如逐一排查Service的Pod副本，检查哪些Pod的服务存在异常问题。

3.Service 相关的接口

点击(此处)折叠或打开

1. /api/v1/proxy/namespaces/{namespace}/services/{name}

四：集群功能模块之间的通信
kubernetes API Server作为集群的核心，负责集群各功能模块之间的通信，集群内各个功能模块通过API Server将信息存入etcd，当需要获取和操作这些数据时，通过API Server提供的REST接口（GET\LIST\WATCH方法）来实现，从而实现各模块之间的信息交互。

1. kubelet与API SERVER交互
每个Node节点上的kubelet定期就会调用API Server的REST接口报告自身状态，API Server接收这些信息后，将节点状态信息更新到etcd中。kubelet也通过API Server的Watch接口监听Pod信息，从而对Node机器上的POD进行管理。

2. kube-controller-manager与API SERVER交互
kube-controller-manager中的Node Controller模块通过API Server提供的Watch接口，实时监控Node的信息，并做相应处理。

3.kube-scheduler与API SERVER交互
Scheduler通过API Server的Watch接口监听到新建Pod副本的信息后，它会检索所有符合该Pod要求的Node列表，开始执行Pod调度逻辑。调度成功后将Pod绑定到目标节点上。

五： 说明
为了缓解各模块对API Server的访问压力，各功能模块都采用缓存机制来缓存数据，各功能模块定时从API Server获取指定的资源对象信息（LIST/WATCH方法），然后将信息保存到本地缓存，功能模块在某些情况下不直接访问API Server，而是通过访问缓存数据来间接访问API Server。

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