f7a89cedda
Adds a document on pod templates that can be shared between various controller docs. Move more philosophical content to later in the doc. Add more task-oriented stuff earlier. Put example config in the document, early on, so users have something concrete to relate the discussion of fields to. Link to Job and DaemonSet docs. Make format more like that of Job and DaemonSet docs. Use jsonpath in examples, which is available in v1.1. Added example files.
2.2 KiB
PLEASE NOTE: This document applies to the HEAD of the source tree
If you are using a released version of Kubernetes, you should refer to the docs that go with that version.
Documentation for other releases can be found at releases.k8s.io.
Pod Templates
Pod templates are pod specifications which are included in other objects, such as Replication Controllers, Jobs, and DaemonSets. Controllers use Pod Templates to make actual pods.
Rather than specifying the current desired state of all replicas, pod templates are like cookie cutters. Once a cookie has been cut, the cookie has no relationship to the cutter. There is no quantum entanglement. Subsequent changes to the template or even switching to a new template has no direct effect on the pods already created. Similarly, pods created by a replication controller may subsequently be updated directly. This is in deliberate contrast to pods, which do specify the current desired state of all containers belonging to the pod. This approach radically simplifies system semantics and increases the flexibility of the primitive.
Future Work
A replication controller creates new pods from a template, which is currently inline in the ReplicationController object, but which we plan to extract into its own resource #170.