label-and-selectors

                          Labels & Selectors

Labels are key/value pairs that are attached to Kubernetes.
They are used as identifying attributes for objects such as pods and replication controller

Selectors:
They are used by the users to select a set of objects.

example:
1. If you have pod running with name- nginx-8glqx

2. for your convience you can label the pod as: 

command:
--->kubecl label pod nginx-8glqx nginx=test  --overwrite

3. if you want to find more details about label, then you can use:
command:
-- kubectl describe pod -l  nginx=test

@master:~/kub-test-folder# kubectl describe deployment -l app=nginx
Name:                   nginx-deployment
Namespace:              default
CreationTimestamp:      Thu, 05 Sep 2019 11:38:20 +0530
Labels:                 app=nginx
                        nginx=test
Annotations:            deployment.kubernetes.io/revision: 1
Selector:               app=nginx



4. to delete the label:
--kubectl delete deployment -l nginx=test
deployment.extensions "nginx-deployment" deleted

-------------------------------------------------------------------------------
 Selectors

selectors allow filtering of keys according to a set of values

apiVersion: v1
kind: Service
metadata:
   name: nginx-app
spec:
   ports:
      - port: 0000
      name: nginx
   type: NodePort
   selector:
      app: nginx ---------> 1