What is the difference between ReplicaSet and ReplicationController?

Question

From what I can tell in the documentation, a ReplicaSet is created when running a Deployment. It seems to support some of the same features of a ReplicationController - scale up

Answer 1

For now, the difference should be insignificant in most cases. ReplicaSet has a generalized label selector: https://github.com/kubernetes/kubernetes/issues/341#issuecomment-140809259. It should support all the features the replication controller supports.

Will ReplicaSet eventually replace ReplicationController? Why would I want to use Deployment and ReplicaSet instead of ReplicationController?

This boils down to rolling update vs deployment. Please read docs on deployment to understand the difference: http://kubernetes.io/docs/user-guide/deployments/. In short, if you start a rolling update and close your laptop, your replicas have some mix of intermediate image versions. If you create a deployement and close your laptop, the deployment either gets POSTed successfully to apiserver, in which case it works server side, or it doesn't, in which case all your replicas are still on the old version.

The bad thing is that nearly all current documentation is about ReplicationControllers.

Agreed, most docs are being updated. Unfortunately docs on the internet are harder to update than the ones on github.