Describe API groups and spec/status for simple kinds

contributors/devel/api-conventions.md

@@ -1,7 +1,7 @@
 API Conventions
 ===============
 
-Updated: 4/22/2016
+Updated: 2/23/2017
 
 *This document is oriented at users who want a deeper understanding of the
 Kubernetes API structure, and developers wanting to extend the Kubernetes API.
@@ -74,6 +74,9 @@ kinds would have different attributes and properties)
 via HTTP to the server. Resources are exposed via:
   * Collections - a list of resources of the same type, which may be queryable
   * Elements - an individual resource, addressable via a URL
+* **API Group** a set of resources that are exposed together at the same. Along
+with the version is exposed in the "apiVersion" field as "GROUP/VERSION", e.g.
+"policy.k8s.io/v1".
 
 Each resource typically accepts and returns data of a single kind. A kind may be
 accepted or returned by multiple resources that reflect specific use cases. For
@@ -82,8 +85,17 @@ to create, update, and delete pods, while a separate "pod status" resource (that
 acts on "Pod" kind) allows automated processes to update a subset of the fields
 in that resource.
 
+Resources are bound together in API groups - each group may have one or more
+versions that evolve independent of other API groups, and each version within
+the group has one or more resources. Group names are typically in domain name
+form - the Kubernetes project reserves use of the empty group, all single
+word names ("extensions", "apps"), and any group name ending in "*.k8s.io" for
+its sole use. When choosing a group name, we recommend selecting a subdomain
+your group or organization owns, such as "widget.mycompany.com".
+
 Resource collections should be all lowercase and plural, whereas kinds are
-CamelCase and singular.
+CamelCase and singular. Group names must be lower case and be valid DNS
+subdomains.
 
 
 ## Types (Kinds)
@@ -156,6 +168,16 @@ API endpoints may deviate from the strict REST pattern and return resources that
 are not singular JSON objects, such as streams of JSON objects or unstructured
 text log data.
 
+A common set of "meta" API objects are used across all API groups and are
+thus considered part of the server group named `meta.k8s.io`. These types may
+evolve independent of the API group that uses them and API servers may allow
+them to be addressed in their generic form. Examples are `ListOptions`,
+`DeleteOptions`, `List`, `Status`, `WatchEvent`, and `Scale`. For historical
+reasons these types are part of each existing API group. Generic tools like
+quota, garbage collection, autoscalers, and generic clients like kubectl
+leverage these types to define consistent behavior across different resource
+types, like the interfaces in programming languages.
+
 The term "kind" is reserved for these "top-level" API types. The term "type"
 should be used for distinguishing sub-categories within objects or subobjects.
 
@@ -276,6 +298,14 @@ cannot vary from the user's desired intent MAY have only "spec", and MAY rename
 Objects that contain both spec and status should not contain additional
 top-level fields other than the standard metadata fields.
 
+Some objects which are not persisted in the system - such as `SubjectAccessReview`
+and other webhook style calls - may choose to add spec and status to encapsulate
+a "call and response" pattern. The spec is the request (often a request for
+information) and the status is the response. For these RPC like objects the only
+operation may be POST, but having a consistent schema between submission and
+response reduces the complexity of these clients.
+
+
 ##### Typical status properties
 
 **Conditions** represent the latest available observations of an object's