The scaling of our application up and down as our resource demands change is useful for many production scenarios, but what about simple application updates? Any production system will have code updates, patches, and feature additions. These could be occurring monthly, weekly, or even daily. Making sure that we have a reliable way to push out these changes without interruption to our users is a paramount consideration.
Once again, we benefit from the years of experience the Kubernetes system is built on. There is built-in support for rolling updates with the 1.0 version. The rolling-update command allows us to update entire ReplicationControllers or just the underlying Docker image used by each replica. We can also specify an update interval, which will allow us to update one pod at a time and wait until proceeding to the next.
Let's take our scaling example and perform a rolling update to the 0.2 version of our container image. We will use an update interval of 2 minutes, so...
