Labels And Selectors For Identifying Objects

Labels can be used to identifying objects. Labels can be applied to all kinds of objects.
Selectors can be used for "filtering" objects by specified selector(s).

Labels in Pods

In a pod def file, labels can exist:

apiVersion: v1
kind: Pod
metadata:
  name: dummy-web-server
  labels:
    app: web-server
    stack-area: frontend
spec:
  containers:
  - name: api-box
    image: api-box-img
    ports:
      - containerPort: 8080

These can be used by the kubectl get command:

kubectl get pods --selector stack-area=frontend

Any other pod that has the same stack-area will appear in the list of pods. Any pod without that label will not appear.

Labels in ReplicaSets

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: dummy-web-server-rs
  labels:
    app: web-server-rs
    stack-area: frontend
spec:
  replicas: 3
  # match replica sets to pods
  selector:
    matchLabels:
      stack-area: frontend
      app: frontend
  # pod defs under the "template" key, sibling of selector+replicas keys
  template:
    metadata:
      labels:
        app: web-server
        stack-area: frontend
    spec:
      containers:
      - name: api-box
        image: api-box-img
        ports:
          - containerPort: 8080

Annotations in ReplicaSets

apiVersion: apps/v1
kind: ReplicaSet
metadata:
  name: dummy-web-server-rs
  labels:
    app: web-server-rs
    stack-area: frontend
  annotations:
    buildVersion: 8.67.5309
spec:
  replicas: 3
  # match replica sets to pods
  selector:
    matchLabels:
      stack-area: frontend
      app: frontend
  # pod defs under the "template" key, sibling of selector+replicas keys
  template:
    metadata:
      labels:
        app: web-server
        stack-area: frontend
    spec:
      containers:
      - name: api-box
        image: api-box-img
        ports:
          - containerPort: 8080

Tags:

Kubernetes