API Overview

This section provides reference information for the Kubernetes API.

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

The Kubernetes API reference lists the API for Kubernetes version v1.21.

For general background information, read The Kubernetes API. Controlling Access to the Kubernetes API describes how clients can authenticate to the Kubernetes API server, and how their requests are authorized.

API versioning

The JSON and Protobuf serialization schemas follow the same guidelines for schema changes. The following descriptions cover both formats.

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

Different API versions indicate different levels of stability and support. You can find more information about the criteria for each level in the API Changes documentation.

Here’s a summary of each level:

  • Alpha:

    • The version names contain alpha (for example, v1alpha1).
    • The software may contain bugs. Enabling a feature may expose bugs. A feature may be disabled by default.
    • The support for a feature may be dropped at any time without notice.
    • The API may change in incompatible ways in a later software release without notice.
    • The software is recommended for use only in short-lived testing clusters, due to increased risk of bugs and lack of long-term support.

  • Beta:

    • The version names contain beta (for example, v2beta3).

    • The software is well tested. Enabling a feature is considered safe. Features are enabled by default.

    • The support for a feature will not be dropped, though the details may change.

    • The schema and/or semantics of objects may change in incompatible ways in a subsequent beta or stable release. When this happens, migration instructions are provided. Schema changes may require deleting, editing, and re-creating API objects. The editing process may not be straightforward. The migration may require downtime for applications that rely on the feature.

    • The software is not recommended for production uses. Subsequent releases may introduce incompatible changes. If you have multiple clusters which can be upgraded independently, you may be able to relax this restriction.

    Note: Please try beta features and provide feedback. After the features exit beta, it may not be practical to make more changes.

  • Stable:

    • The version name is vX where X is an integer.
    • The stable versions of features appear in released software for many subsequent versions.

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.

There are several API groups in Kubernetes:

  • The core (also called legacy) group is found at REST path /api/v1. The core group is not specified as part of the apiVersion field, for example, apiVersion: v1.
  • The named groups are at REST path /apis/$GROUP_NAME/$VERSION and use apiVersion: $GROUP_NAME/$VERSION (for example, apiVersion: batch/v1). You can find the full list of supported API groups in Kubernetes API reference.

Enabling or disabling API groups

Certain resources and API groups are enabled by default. You can enable or disable them by setting --runtime-config on the API server. The --runtime-config flag accepts comma separated <key>[=<value>] pairs describing the runtime configuration of the API server. If the =<value> part is omitted, it is treated as if =true is specified. For example:

  • to disable batch/v1, set --runtime-config=batch/v1=false
  • to enable batch/v2alpha1, set --runtime-config=batch/v2alpha1

Note: When you enable or disable groups or resources, you need to restart the API server and controller manager to pick up the --runtime-config changes.

Persistence

Kubernetes stores its serialized state in terms of the API resources by writing them into etcd.

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