The ReplicationController will ensure a specified number of pod replicas will run at all time.
Pods created with ReplicationController will automatically be replaced if they fail, get deleted or are terminated.
A ReplicationController is similar to a process supervisor, but instead of supervising individual processes on a single node, the ReplicationController supervises multiple pods across multiple nodes.
ReplicationController is often abbreviated to "rc" in discussion, and as a shortcut in kubectl commands.
The ReplicationController helps up run multiple instances of a single pod in the Kubernetes cluster thus providing high availability. Even if you have a single pod the ReplicationController can help by automatically bringing up a new pod when the existing one fails. Thus the ReplicationController that the specified number of pods are runing at all times even it is just one or one hundred.
The ReplicationController spans across multiple nodes in the cluster.
ReplicationController is the older technology that is being replaced by Replica Set. Replica Set is the new, recommended way to setup the replication.