.. _glossary:

========
Glossary
========

Magnum Terminology
~~~~~~~~~~~~~~~~~~

.. glossary::

Cluster (previously Bay)
  A cluster is the construct in which Magnum launches container orchestration
  engines. After a cluster has been created the user is able to add containers
  to it either directly, or in the case of the Kubernetes container
  orchestration engine within pods - a logical construct specific to that
  implementation. A cluster is created based on a ClusterTemplate.

ClusterTemplate (previously BayModel)
  A ClusterTemplate in Magnum is roughly equivalent to a flavor in Nova. It
  acts as a template that defines options such as the container orchestration
  engine, keypair and image for use when Magnum is creating clusters using
  the given ClusterTemplate.

Container Orchestration Engine (COE)
  A container orchestration engine manages the lifecycle of one or more
  containers, logically represented in Magnum as a cluster. Magnum supports a
  number of container orchestration engines, each with their own pros and cons,
  including Docker Swarm, Kubernetes, and Mesos.

Labels
  Labels is a general method to specify supplemental parameters that are
  specific to certain COE or associated with certain options.  Their
  format is key/value pair and their meaning is interpreted by the
  drivers that uses them.

Cluster Drivers
  A cluster driver is a collection of python code, heat templates, scripts,
  images, and documents for a particular COE on a particular distro. Magnum
  presents the concept of ClusterTemplates and clusters. The implementation
  for a particular cluster type is provided by the cluster driver. In other
  words, the cluster driver provisions and manages the infrastructure for the
  COE.

Kubernetes Terminology
~~~~~~~~~~~~~~~~~~~~~~

.. glossary::

Kubernetes uses a range of terminology that we refer to in this guide. We
define these common terms for your reference:

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 clusters. Refer to the
  `pods section <https://kubernetes.io/docs/concepts/workloads/pods/pod-overview/>`_ in
  `Kubernetes Tasks`_ 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 `replication
  controller section
  <https://kubernetes.io/docs/tasks/run-application/rolling-update-replication-controller/>`_ in
  the `Kubernetes Tasks`_ 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
  `services section
  <https://kubernetes.io/docs/concepts/services-networking/service/>`_ in
  `Kubernetes Concepts`_ for more information.

.. _Kubernetes Tasks: https://kubernetes.io/docs/tasks/
.. _Kubernetes Concepts: https://kubernetes.io/docs/concepts/