Kubernetes报错:MatchExpressions:[]v1.LabelSelectorRequirement(nil)}: field is immutable

报错信息

MatchExpressions:[]v1.LabelSelectorRequirement(nil)}: field is immutable

原因

原因：这个问题的本质原因是，两个相同的Deployment（一个已部署，一个要部署），但它们选择器不同。

场景复现

例：
app.yaml

apiVersion: apps/v1                                                                  kind: Deployment
metadata:
  name: my-app
  labels:
    app: my-app
spec:
  replicas: 10
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
        version: v1.0.0
      annotations:
        prometheus.io/scrape: "true"
        prometheus.io/port: "9101"
    spec:
      containers:
      - name: my-app
        image: containersol/k8s-deployment-strategies
        ports:
        - name: http
          containerPort: 8080
        - name: probe
          containerPort: 8086
        env:
        - name: VERSION
          value: v1.0.0
        livenessProbe:
          httpGet:
            path: /live
            port: probe
          initialDelaySeconds: 5
          periodSeconds: 5
        readinessProbe:
          httpGet:
            path: /ready
            port: probe
          periodSeconds: 5

部署完成之后，查看一下结果

$kubectl get deployment
NAME     READY   UP-TO-DATE   AVAILABLE   AGE
my-app   10/10   10           10          84s

接下来，我们修改deployment的选择器，主要内容如下

spec:
  replicas: 10
  selector:
    matchLabels:
      app: my-app-change
  template:
    metadata:
      labels:
        app: my-app-change
        version: v1.0.0

完成文件如下:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
  labels:
    app: my-app
spec:
  replicas: 10
  selector:
    matchLabels:
      app: my-app-change
  template:
    metadata:
      labels:
        app: my-app-change
        version: v1.0.0
      annotations:
        prometheus.io/scrape: "true"
        prometheus.io/port: "9101"
    spec:
      containers:
      - name: my-app
        image: containersol/k8s-deployment-strategies
        ports:
        - name: http
          containerPort: 8080
        - name: probe
          containerPort: 8086
        env:
        - name: VERSION
          value: v1.0.0
        livenessProbe:
          httpGet:
            path: /live
            port: probe
          initialDelaySeconds: 5
          periodSeconds: 5
        readinessProbe:
          httpGet:
            path: /ready
            port: probe
          periodSeconds: 5

部署的时候，会出现如下报错：

$kubectl apply -f app.yaml
The Deployment "my-app" is invalid: spec.selector: Invalid value: v1.LabelSelector{MatchLabels:map[string]string{"app":"my-app-change"}, MatchExpressions:[]v1.LabelSelectorRequirement(nil)}: field is immutable

可以看已经部署的deployment的selector：

$kubectl describe deployment my-app
Name:                   my-app
...
Selector:               app=my-app
...

可以看到deployment名字为my-app的已经有了选择器，内容为app=my-app。而此时，报错的原因是因为新部署的deployment名字也为my-app，但是选择器的内容是app=my-app-change。

解决方式：

1： 可以将原先的deployment删除后再部署
2： 修改deployment的名字，不要重名