Define kubernetes ReplicaSets with Example and commands:

A ReplicaSet’s purpose is to maintain a stable set of replica Pods running at any given time. As such, it is often used to guarantee the availability of a specified number of identical Pods

There are many ways we can use replicasets such that always required number of pods running is guarangteed.

1. While creating the deployment

 kubectl create deployment pradeepa--image=scmgalaxy/nginx-devopsschoolv1 --replicas=3 -n=pradeepa

2. While the deployment is running

kubectl edit deploy pradeepa-n=pradeepa
Replicas:               2 desired | 2 updated | 2 total | 2 available | 0 unavailable //change this value to desired number of replicas

3. Using scale option

kubectl scale --replicas=1 deploy/pradeepa-n=pradeepa

Always the required number of pods are running is guaranteed.

[centos@ip-172-31-22-14 pradeepa]$ kubectl create deployment pradeepa--image=scmgalaxy/nginx-devopsschoolv1 --replicas=3 -n=pradeepa
deployment.apps/pradeepa created
[centos@ip-172-31-22-14 pradeepa]$ kubectl get deploy -n=pradeepa
NAME READY UP-TO-DATE AVAILABLE AGE
pradeepa 3/3 3 3 9s
[centos@ip-172-31-22-14 pradeepa]$ kubectl get pods -n=pradeepa
NAME READY STATUS RESTARTS AGE
pradeepa-88bcb4f5d-9jq4d 1/1 Running 0 18s
pradeepa-88bcb4f5d-dtn2c 1/1 Running 0 18s
pradeepa-88bcb4f5d-hppkz 1/1 Running 0 18s
[centos@ip-172-31-22-14 pradeepa]$ kubcectl delete pod pradeepa-88bcb4f5d-hppkz -n=pradeepa
-bash: kubcectl: command not found
[centos@ip-172-31-22-14 pradeepa]$ kubectl delete pod pradeepa-88bcb4f5d-hppkz -n=pradeepa
pod "pradeepa-88bcb4f5d-hppkz" deleted
[centos@ip-172-31-22-14 pradeepa]$ kubectl get pods
NAME READY STATUS RESTARTS AGE
pradeepa1/1 Running 0 93m
[centos@ip-172-31-22-14 pradeepa]$ kubectl get pods -n=pradeepa
NAME READY STATUS RESTARTS AGE
pradeepa-88bcb4f5d-9jq4d 1/1 Running 0 52s
pradeepa-88bcb4f5d-dtn2c 1/1 Running 0 52s
pradeepa-88bcb4f5d-qms2q 1/1 Running 0 10s //this is the newly created pod after deleting the existing POD