Merge "Add Pod, Service, Replication Controller terms"

doc/source/userguide.rst

@@ -54,6 +54,34 @@ Container Orchestration Engine (COE)
   number of container orchestration engines, each with their own pros and cons,
   including Docker Swarm, Kubernetes, and Mesos.
 
+Pod
+  When using the Kubernetes container orchestration engine, a pod is the
+  smallest deployable unit that can be created and managed. A pod is a
+  co-located group of application containers that run with a shared context.
+  When using Magnum, pods are created and managed within bays. Refer to the
+  `Kubernetes User Guide
+  <http://kubernetes.io/v1.0/docs/user-guide/pods.html>`__ for more
+  information.
+
+Replication controller
+  A replication controller is used to ensure that at any given time a certain
+  number of replicas of a pod are running. Pods are automatically created and
+  deleted by the replication controller as necessary based on a template to
+  ensure that the defined number of replicas exist. Refer to the `Kubernetes
+  User Guide
+  <http://kubernetes.io/v1.0/docs/user-guide/replication-controller.html>`__
+  for more information.
+
+Service
+  A service is an additional layer of abstraction provided by the Kubernetes
+  container orchestration engine which defines a logical set of pods and a
+  policy for accessing them. This is useful because pods are created and
+  deleted by a replication controller, for example, other pods needing to
+  discover them can do so via the service abstraction. Refer to the
+  `Kubernetes User Guide
+  <http://kubernetes.io/v1.0/docs/user-guide/services.html>`__ for more
+  information.
+
 ========
 Overview
 ========