1.Label

标签(labels)：附加到 k8s 对象上的键值对。用于指定对用户有意义且相关的对象的标识属性。

示例标签：

• "release" : "stable", "release" : "canary"
• "environment" : "dev", "environment" : "qa", "environment" : "production"
• "tier" : "frontend", "tier" : "backend", "tier" : "cache"
• "partition" : "customerA", "partition" : "customerB"
• "track" : "daily", "track" : "weekly"

推荐使用的标签：

apiVersion: apps/v1
kind: StatefulSet
metadata:
  labels:
    app.kubernetes.io/name: mysql
    app.kubernetes.io/instance: mysql-abcxzy
    app.kubernetes.io/version: "5.7.21"
    app.kubernetes.io/managed-by: helm
    app.kubernetes.io/component: database
    app.kubernetes.io/part-of: wordpress
...

2. 语法

Label Key:

• 不超过63个字符
• 支持使用前缀，前缀必须是DNS子域，不超过253个字符。系统化组件创建的label必须指定前缀。kubernetes.io 和 k8s.io 由 kubernetes 保留
• 格式：[A-Za-z0-9][A-Za-z0-9_\-\.]

Label Value:

• 不超过63个字符
• 格式：[A-Za-z0-9][A-Za-z0-9_\-\.]

3. Label selector

Label 不是唯一的，很多对象可能有相同的label

通过 label selector，可指定一个object集合，通过 label selector 对 object 集合进行操作

两种类型：

• equality-based: 使用=, ==, != 操作符，可使用逗号分隔多个表达式： environment=production,tier!=frontend

• set-based：使用in, notin, !操作符。! 表示没有该 label 的 object

$ kubectl get pods -l environment=production,tier=frontend
$ kubectl get pods -l 'environment in (production),tier in (frontend)'
$ kubectl get pods -l 'environment in (production, qa)'
$ kubectl get pods -l 'environment,environment notin (frontend)'

4. API

• Service

  spec.selector = map[string]string

  selector:
    component: redis
  

• Deployment, StatefulSet, DaemonSet, ReplicaSet, Job

  sepc.selector.matchLabels = map[string]string

  sepc.selector.matchExpressions:

  • key: string
  • operator: In, NotIn, Exists or DoesNotExist
  • values: []string

  selector:
    matchLabels:
      component: redis
    matchExpressions:
      - {key: tier, operator: In, values: [cache]}
      - {key: environment, operator: NotIn, values: [dev]}
  

• node affinity 和 pod affinity 中的 selector

  spec.template.spec.affinity.nodeAffinity:

  • requiredDuringSchedulingIgnoredDuringExecution.nodeSelectorTerms
  • preferredDuringSchedulingIgnoredDuringExecution.preference
    • matchExpressions: by node labels
      • key: string
      • operator: In, NotIn, Exists, DoesNotExist, Gt or Lt
      • values: []string
    • matchFields: by node fields
      • key: string
      • operator: In, NotIn, Exists, DoesNotExist, Gt or Lt
      • values: []string

  spec.template.spec.affinity.podAffinity.requiredDuringSchedulingIgnoredDuringExecution

  spec.template.spec.affinity.podAffinity.preferredDuringSchedulingIgnoredDuringExecution.podAffinityTerm

  spec.template.spec.affinity.podAntiAffinity.requiredDuringSchedulingIgnoredDuringExecution

  spec.template.spec.affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution.podAffinityTerm

  • labelSelector:
    • matchExpressions:
      • key: string
      • operator: In, NotIn, Exists or DoesNotExist
      • values: []string
    • matchLabels: map[string]string
  • namespaceSelector:
    • matchExpressions:
      • key: string
      • operator: In, NotIn, Exists or DoesNotExist
      • values: []string
    • matchLabels: map[string]string

  affinity:
      nodeAffinity:
        requiredDuringSchedulingIgnoredDuringExecution:
          nodeSelectorTerms:
          - matchExpressions:
            - key: kubernetes.io/hostname
              operator: In
              values:
              - k8s-node01
              - k8s-node02
        preferredDuringSchedulingIgnoredDuringExecution:
        - weight: 1
          preference:
            matchExpressions:
            - key: another-node-label-key
              operator: In
              values:
              - another-node-label-value
      podAntiAffinity:
        preferredDuringSchedulingIgnoredDuringExecution:
        - podAffinityTerm:
            labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - kafka-container
            topologyKey: kubernetes.io/hostname
          weight: 100