If we have to add a container in pod but without deleting existing pod,what is best way to do it.
I don’t think there is one.
Pods, once deployed, are immutable. If you need to make changes you need to edit its definition and add the additional container into the definition. Then apply the definition.
This will destroy the running container and create a new container though. I don’t think keeping the pod alive and apply changes is possible.
Keep in mind: In some cases it makes sense to have two containers per pod, in general you should only have one container per pod though. So make the decision to put two containers into one pod very consciously and see if there are other options where you don’t have to do that.