Question
What is a ReplicationController in Kubernetes?
Answer
It is a component that ensures the pods are constantly running (page 90 and 91 of Kubernetes in Action by Luksa). They were designed to create and manage redundant pods (page 91 of Kubernetes in Action by Luksa). They do just that -- they do not transfer pods but create new ones on different nodes (page 93 of Kubernetes in Action by Luksa).
There are three parts to ReplicationControllers: a label selector, a replica count, and a pod template (page 92 of Kubernetes in Action by Luksa).
They are created with a JSON or YAML file (page 93 of Kubernetes in Action by Luksa). If you post this file to the Kubernetes API server, a ReplicationController will be created and pods according to its specification including the number of pods, their label(s), the image of the container for the pods, and the container port values (page 94 of Kubernetes in Action by Luksa).