Using ReplicaSets

ReplicaSets are the simplest Kubernetes Pod controller resource. They replace the older ReplicationController resource.

The major difference between a ReplicaSet and a ReplicationController is that a ReplicationController uses a more basic type of selector – the filter that determines which Pods should be controlled.

While ReplicationControllers use simple equity-based (key=value) selectors, ReplicaSets use a selector with multiple possible formats, such as matchLabels and matchExpressions, which will be reviewed in this chapter.

Important note

There shouldn't be any reason to use a ReplicationController over a ReplicaSet – just stick with ReplicaSets unless you have a really good reason not to.

ReplicaSets allow us to inform Kubernetes to maintain a certain number of Pods for a particular Pod spec. The YAML for a ReplicaSet is very similar to that for a Pod. In fact, the entire Pod spec is nested in the ReplicaSet YAML, under the...