Reference Documentation

Design docs, concept definitions, and references for APIs and CLIs.

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Kubernetes API Overview

This page contains an overview of the Kubernetes API.

The REST API is the fundamental fabric of Kubernetes. All operations and communications between components are REST API calls handled by the API Server, including external user commands. Consequently, everything in the Kubernetes platform is treated as an API object and has a corresponding entry in the API.

Most operations can be performed through the kubectl command-line interface or other command-line tools, such as kubeadm, which in turn use the API. However, the API can also be accessed directly using REST calls.

Consider using one of the client libraries if you are writing an application using the Kubernetes API.

API versioning

To make it easier to eliminate fields or restructure resource representations, Kubernetes supports multiple API versions, each at a different API path, such as /api/v1 or /apis/extensions/v1beta1.

The version is set at the API level rather than at the resource or field level to ensure that the API presents a clear, consistent view of system resources and behavior, and to enable controlling access to end-of-life and/or experimental APIs. The JSON and Protobuf serialization schemas follow the same guidelines for schema changes; all descriptions below cover both formats.

Note that API versioning and software versioning are only indirectly related. The API and release versioning proposal describes the relationship between API versioning and software versioning.

Different API versions imply different levels of stability and support. The criteria for each level are described in more detail in the API Changes documentation.

The criteria are summarized here:

API groups

API groups make it easier to extend the Kubernetes API. The API group is specified in a REST path and in the apiVersion field of a serialized object.

Currently, there are several API groups in use:

There are two supported paths to extending the API with custom resources:

  1. CustomResourceDefinition is for users with very basic CRUD needs.
  2. Coming soon: users needing the full set of Kubernetes API semantics can implement their own apiserver and use the aggregator to make it seamless for clients.

Enabling API groups

Certain resources and API groups are enabled by default. You can enable or disable them by setting --runtime-config on apiserver. --runtime-config accepts comma separated values. For example, to disable batch/v1, set --runtime-config=batch/v1=false, to enable batch/v2alpha1, set --runtime-config=batch/v2alpha1. The flag accepts comma separated set of key=value pairs describing runtime configuration of the apiserver.

IMPORTANT: Enabling or disabling groups or resources requires restarting apiserver and controller-manager to pick up the --runtime-config changes.

Enabling resources in the groups

DaemonSets, Deployments, HorizontalPodAutoscalers, Ingress, Jobs and ReplicaSets are enabled by default. You can enable other extensions resources by setting --runtime-config on apiserver. --runtime-config accepts comma separated values. For example, to disable deployments and jobs, set --runtime-config=extensions/v1beta1/deployments=false,extensions/v1beta1/jobs=false


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