Even though the Replica Set is a very powerful concept, there is one part of it that we have not talked about: what happens when we apply a new configuration to a Replica Set in order to upgrade our applications? How does it handle the fact that we want to keep our application alive 100% of the time without service interruption?
Well, the answer is simple: it doesn't. If you apply a new configuration to a Replica Set with a new version of the image, the Replica Set will destroy all the Pods and create newer ones without any guaranteed order or control. In order to ensure that our application is always up with a guaranteed minimum amount of resources (Pods), we need to use Deployments.
First, take a look at what a deployment looks ...
