Replication

In Kubernetes the role of ReplicaSet/ReplicationController is to ensure we have always X pod up and running.

ReplicationController

kubectl create -f rc-definition.yaml
kubectl get replicattioncontroller
kubectl get pods

ReplicaSet

It selects the pods it needs to monitor and keep an eye on through labels. And replica set uses the template section in the yaml file to start a new pod when one of the pods fail.

kubectl apply -f rs-definition.yaml
kubectl scale --replicas=6 -f rs-definition.yaml # overrides the replicas directive in the yaml file. 

Here are some useful commands:

kubectl create -f rs-definition.yaml # You can use either apply or create
kubectl get name-of-replicaset
kubectl delete replicaset name-of-replicaset # It will delete all the pods it created for the replica set while deleting the replica set
kubectl replace -f new-rs-definition.yaml
kubectl get replicasets.apps

[!TIP]

You can always edit a replicaset configuration live by using this command: kubectl edit replicaset replicaset-name

Keep in mind this is a in memory file k8s creates for itself and won’r be persisted. But changes there are applied immediately.