A ReplicationController ensures that
a specified number of pod replicas are running at any one time. In other words,
a ReplicationController makes sure that a pod or a homogeneous set of pods is
always up and available.
How a
ReplicationController Works
If there are too many pods, the ReplicationController terminates the extra pods. If there are too few, the ReplicationController starts more pods. Unlike manually created pods, the pods maintained by a ReplicationController are automatically replaced if they fail, are deleted, or are terminated. For example, your pods are re-created on a node after disruptive maintenance such as a kernel upgrade. For this reason, you should use a ReplicationController even if your application requires only a single pod.
LAB
1. Replication Controller YAML file
2. Create and display
kubectl create -f nginx-rc.yaml
kubectl get po -o wide
kubectl get po -l app=nginx-app
kubectl get rc nginx-rc
kubectl describe rc nginx-rc
*******************************************************************
# 3. Reschedule
kubectl get po -o wide --watch
kubectl get po -o wide
kubectl get nodes
*******************************************************************
# 4. Scaling up cluster
kubectl scale rc nginx-rc --replicas=5
kubectl get rc nginx-rc
kubectl get po -o wide
*******************************************************************
# 5. Scalling down
kubectl scale rc nginx-rc --replicas=3
kubectl get rc nginx-rc
kubectl get po -o wide
*******************************************************************
# 6. Cleanup
kubectl delete -f nginx-rc.yaml
kubectl get rc
kubectl get po -l app=nginx-app
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