Glossary¶

Magnum Terminology¶

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¶

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 in the Kubernetes User Guide 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 in the Kubernetes User Guide 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 in the Kubernetes User Guide for more information.