You can add labels to pods, services and deployments either at build time or at run time. If you're adding labels at build time, you can add a label section in the metadata portion of the YAML as shown below:

apiVersion: v1
kind: Pod
metadata:
  name: helloworld
  labels:
    env: production
    author: karthequian
    application_type: ui
    release-version: "1.0"
spec:
  containers:
  - name: helloworld
    image: karthequian/helloworld:latest

You can deploy the code above by using the command kubectl create -f helloworld-pod-with-labels.yml

kubectl get pods --show-labels.

kubectl label po/helloworld app=helloworld. This adds the label app with the value helloworld to the pod.

To update the value of a label, use the --overwrite flag in the command as follows: kubectl label po/helloworld app=helloworldapp --overwrite

To remove an existing label, just add a - to the end of the label key as follows: kubectl label po/helloworld app-. This will remove the app label from the helloworld pod.

• You can search for labels with the flag --selector (or -l). If you want to search for all the pods that are running in production, you can run kubectl get pods --selector env=production
• You can also do more complicated searches, like finding any pods owned by Karthik in the development tier, by the following query dev-lead=karthik,env=staging: kubectl get pods -l dev-lead=karthik,env=staging
• Or, any apps not owned by Karthik in staging (using the ! construct): kubectl get pods -l dev-lead!=karthik,env=staging
• Querying also supports the in keyword kubectl get pods -l 'release-version in (1.0,2.0)'
• Or a more complicated example: kubectl get pods -l "release-version in (1.0,2.0),team in (marketing,ecommerce)"
• The opposite of "in" is "notin". Surprise. "Notin" is supported as well, as shown in this example: kubectl get pods -l 'release-version notin (1.0,2.0)'

Labels will also work with kubectl get services/deployments/all --show-labels and will return labels for your services, deployments or all objects. kubectl get all --show-labels

And, you can delete pods, services or deployments by label as well! For example kubectl delete pods -l dev-lead=karthik will delete all pods who's dev-lead was Karthik.