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Labels and Selectors

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In this section, we will take a look at Labels and Selectors

Labels and Selectors are standard methods to group things together.

Labels are properties attached to each item.

Selectors help you to filter these items

How are labels and selectors are used in kubernetes?

• We have created different types of objects in kubernetes such as PODs, ReplicaSets, Deployments etc.

  

How do you specify labels?

    apiVersion: v1
    kind: Pod
    metadata:
     name: simple-webapp
     labels:
       app: App1
       function: Front-end
    spec:
     containers:
     - name: simple-webapp
       image: simple-webapp
       ports:
       - containerPort: 8080

Once the pod is created, to select the pod with labels run the below command

$ kubectl get pods --selector app=App1

Kubernetes uses labels to connect different objects together

    apiVersion: apps/v1
    kind: ReplicaSet
    metadata:
      name: simple-webapp
      labels:
        app: App1
        function: Front-end
    spec:
     replicas: 3
     selector:
       matchLabels:
        app: App1
     template:
       metadata:
         labels:
           app: App1
           function: Front-end
       spec:
         containers:
         - name: simple-webapp
           image: simple-webapp   

For services

  ```
  apiVersion: v1
  kind: Service
  metadata:
   name: my-service
  spec:
   selector:
     app: App1
   ports:
   - protocol: TCP
     port: 80
     targetPort: 9376 
   ```   ![lrs1](/k8s.github.io/images/lrs1.PNG)

Annotations

• While labels and selectors are used to group objects, annotations are used to record other details for informative purpose.

    apiVersion: apps/v1
    kind: ReplicaSet
    metadata:
      name: simple-webapp
      labels:
        app: App1
        function: Front-end
      annotations:
         buildversion: 1.34
    spec:
     replicas: 3
     selector:
       matchLabels:
        app: App1
    template:
      metadata:
        labels:
          app: App1
          function: Front-end
      spec:
        containers:
        - name: simple-webapp
          image: simple-webapp   
  

  

K8s Reference Docs:

• https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/