Kubernetes deployment is designed to help you with scaling applications up and down as per your need. Let's say you want to scale your application from 3 replicas to 10. You can do this by running the following command:
kubectl scale deployments nginx --replicas=10
Let's verify,
kubectl get pods -l app=frontend
You will see the following output where some of the pods are still in the ContainerCreating phase. After some time you will see all the pods are in a Running state.
NAME READY STATUS RESTARTS AGE
nginx-776567f984-4vrmn 0/1 ContainerCreating 0 3s
nginx-776567f984-5556g 1/1 Running 0 3s
nginx-776567f984-8z8mj 0/1 ContainerCreating 0 3s
nginx-776567f984-9s2jb 1/1 Running 0 3m45s
nginx-776567f984-9sbdd 0/1 ContainerCreating 0 3s
nginx-776567f984-dnp6s 0/1 ContainerCreating 0 3s
nginx-776567f984-p9qf8 0/1 ContainerCreating 0 3s
nginx-776567f984-sdrns 1/1 Running 0 3m45s
nginx-776567f984-vplg9 0/1 ContainerCreating 0 3s
nginx-776567f984-vxdzw 1/1 Running 0 3m45s
If you want to scale down the application replicas, say from 10 to 2, you can do this by running the following command:
kubectl scale deployments nginx --replicas=2
Verify it using kubectl get pods -l app=frontend. Some of the pods will be in the Terminating state.
NAME READY STATUS RESTARTS AGE
nginx-776567f984-4vrmn 1/1 Terminating 0 112s
nginx-776567f984-5556g 1/1 Terminating 0 112s
nginx-776567f984-8z8mj 1/1 Terminating 0 112s
nginx-776567f984-dnp6s 0/1 Terminating 0 112s
nginx-776567f984-p9qf8 1/1 Terminating 0 112s
nginx-776567f984-sdrns 1/1 Running 0 5m34s
nginx-776567f984-vxdzw 1/1 Running 0 5m34s
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