kubernetes patch学习小结

kubernetes patch操作

• PUT操作 /<资源名复数形式>/<名字> 通过给出的资源名和客户端提供的json对象来更新或创建资源

• PATCH操作 /<资源名复数形式>/<名字> 选择修改资源详细指定的域

  • Kubernetes使用Patch命令来对运行中的应用进行动态跟新
  • 对于patch操作，kubernetes API通过相应的HTTP首部"Content-Type"对其进行识别

• PATCH API对象的三种方式

  • JSON Patch，Content-Type: application/json-patch+json

    在RFC6902定义中，JSON Patch是执行在资源对象上的一系列操作，进行局部更新。例如：

    {"op":"add", "path": "/a/b/c", "value": ["foo", "bar"]}
    

  • Merge Patch，Content-Type: application/merge-json-patch+json。

    Merge Patch必须包含一个对资源对象的部分描述，json对象。该json对象被提交到服务端，并和服务端的当前对象进行合并，从而创建新的对象。完整的替换列表，也就是说，新的列表定义会替换原有的定义。

  • JSON strategic merge patch，这种补丁是以增量的形式来对已有的定义进行修改，可以理解为类似于linux diff创建的补丁。

• PATCH 示例

  // 示例1
  {
      "a":{
          "b":{
              "c":"foo"
          }
      }
  }
   
  // JSON Patch 操作
  [
    { "op": "test", "path": "/a/b/c", "value": "foo" },
    { "op": "remove", "path": "/a/b/c" },
    { "op": "add", "path": "/a/b/c", www.tianhengyl1.com/ "value": [ "foo", "bar" ] },
    { "op": "replace", "path":www.ysgj1688.com  "/a/b/c", "value": 42 },
    { "op": "move", "from": www.baohuayule.net "www.089188.cn /a/b/c"www.taohuayuan178.com , "path": "/a/b/d" },
    { "op": "copy", "from": "/a/b/d",www.qinlinyule.cn "path": "/a/b/e" }
  ]
  
  // 示例2
  {
  	"users" : [
  		    		{ "name" : "Alice" , "email" : "[email protected]" },
      { "name" : "Bob" , "email" : "[email protected]" }
     	]
  }
  
  patch操作
  [
  	  {
      		"op" : "replace" ,
  				    "path" : "/users/0/email" ,
  		    "value" : "[email protected]"
  	  },
    	{
  		    "op" : "add" ,
      		"path" : "/users/-" ,
      		"value" : {
        			"name" : "Christine",
       			 "email" : "[email protected]"
  		  }
  	}
  ]
  
  结果
  {
  	"users" : [
      		{ "name" : "Alice" , "email" : "[email protected]" },
      		{ "name" : "Bob" , "email" : "[email protected]" },
      		{ "name" : "Christine" , "email" : "[email protected]" }
     			]
  }
  

strategic merge patch to update a Deployment

示例

apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: patch-demo
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: patch-demo-ctr
        image: nginx
      tolerations:
      - effect: NoSchedule
        key: dedicated
        value: test-team

创建deployment

kubectl apply -f deployment-patch.yaml

每个pod运行一个容器。现在patch操作使pod 运行两个容器: nginx和redis

patch-file-containers.yaml 文件内容:

spec:
  template:
    spec:
      containers:
      - name: patch-demo-ctr-2
        image: redis

kubectl patch deployment patch-demo --patch "$(cat patch-file-containers.yaml)"

kubectl get deployment patch-demo -o yaml

   containers:
      - image: redis
        imagePullPolicy: Always
        name: patch-demo-ctr-2
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File
      - image: nginx
        imagePullPolicy: Always
        name: patch-demo-ctr
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File

可以看到每个pod运行两个容器。

注意

上述操作 patch称为 a strategic merge patch。patch操作没有替换 containers 列表，相反在列表中添加新的容器。merge进patch操作进入存在的列表中。 可能在某些情况下会进行替换，而不是merge列表操作。a strategic merge patch 列表要么被替换要么被merge取决于patch策略。源码中通过 patchStrategy 键值指定。如下示：

type PodSpec struct {
  ...
  Containers []Container `json:"containers" patchStrategy:"merge" patchMergeKey:"name" ...`
  Tolerations []Toleration `json:"tolerations,omitempty" opt,name=tolerations"`

上述可以看出Tolerations列表就会被替换，而不是merge操作。原因是没有patchStrategy键值，所有the strategic merge patch 使用默认的replace patch策略。

示例省略，详细的toleration patch可参考官网示例。

JSON merge patch to update a Deployment

A strategic merge patch 与 JSON merge patch有所不同。a JSON merge patch，如果你想去更新列表必须指定完整的新列表，新列表将进行完全替换。

kubectl patch xxxx --type xxxx --patch xxxx

默认的type参数是strategic。

示例

创建文件patch-file-2.yaml

spec:
  template:
    spec:
      containers:
      - name: patch-demo-ctr-3
        image: gcr.io/google-samples/node-hello:1.0 // redis

kubectl patch deployment patch-demo --type merge --patch "$(cat patch-file-2.yaml)"

注：镜像拉取可能会产生问题，换个redis镜像。

kubectl get deployment patch-demo --output yaml

   spec:
      containers:
      - image: redis
        imagePullPolicy: Always
        name: patch-demo-ctr-3
        resources: {}
        terminationMessagePath: /dev/termination-log
        terminationMessagePolicy: File

json格式的更新 patch-file.json

{
   "spec": {
      "template": {
         "spec": {
            "containers": [
               {
                  "name": "patch-demo-ctr-2",
                  "image": "redis"
               }
            ]
         }
      }
   }
}

kubectl patch deployment patch-demo --patch "$(cat patch-file.yaml)"
kubectl patch deployment patch-demo --patch 'spec:\n template:\n  spec:\n   containers:\n   - name: patch-demo-ctr-2\n     image: redis'

kubectl patch deployment patch-demo --patch "$(cat patch-file.json)"
kubectl patch deployment patch-demo --patch '{"spec": {"template": {"spec": {"containers": [{"name": "patch-demo-ctr-2","image": "redis"}]}}}}'

json patch

总结

kubectl patch用于更改Deployment对象的实时配置，并没有更改最初用于创建Deployment对象的配置文件。用于更新API对象的其他命令包括 kubectl annotate， kubectl edit， kubectl replace， kubectl scale和kubectl apply。

本文主要是介绍patch操作及put操作区别，kubernetes几种patch操作，以及后续我们在接口中如何使用patch操作实时更新对象。

参考文档

JSON Patch: https://blog.csdn.net/li123128/article/details/80321815
PATCH和PUT方法的区别？: https://blog.csdn.net/varyall/article/details/80895945
JSON Patch and JSON Merge Patch: http://erosb.github.io/post/json-patch-vs-merge-patch/
Update API Objects in Place Using kubectl patch: https://kubernetes.io/docs/tasks/run-application/update-api-object-kubectl-patch/