Updated for adherence to style guide and the links to: /docs/user-gui… (#7817)
* Updated for adherence to style guide and the links to: /docs/user-guide/kubectl Can someone please confirm what the "Coming soon" path to extend the API with custom resources is? * Incorporated the changes suggested @heckj @zacharysarah Could one of you please confirm What "Coming soon: " in line 82 stands for? Is there a name or definition or reference? * Update api-overview.md * Update api-overview.md * fixed a typo * Update api-overview.mdpull/7865/merge
Rajakavitha1
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@ -8,55 +8,62 @@ approvers:
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---
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{% capture overview %}
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This page contains an overview of the Kubernetes API.
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This page provides an overview of the Kubernetes API.
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{% endcapture %}
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{% capture body %}
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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
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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
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platform is treated as an API object and has a corresponding entry in the
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[API](/docs/reference/generated/kubernetes-api/{{page.version}}/).
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Most operations can be performed through the
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[kubectl](/docs/user-guide/kubectl-overview/) command-line interface or other
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command-line tools, such as [kubeadm](/docs/admin/kubeadm/), which in turn use
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the API. However, the API can also be accessed directly using REST calls.
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[kubectl](/docs/reference/kubectl/overview/) command-line interface or other
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command-line tools, such as [kubeadm](/docs/reference/setup-tools/kubeadm/kubeadm/), which in turn use
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the API. However, you can also access the API directly using REST calls.
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Consider using one of the [client libraries](/docs/reference/client-libraries/)
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if you are writing an application using the Kubernetes API.
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## API versioning
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To make it easier to eliminate fields or restructure resource representations, Kubernetes supports
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multiple API versions, each at a different API path, such as `/api/v1` or
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To eliminate fields or restructure resource representations, Kubernetes supports
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multiple API versions, each at a different API path. For example: `/api/v1` or
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`/apis/extensions/v1beta1`.
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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.
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The version is set at the API level rather than at the resource or field level to:
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- Ensure that the API presents a clear and consistent view of system resources and behavior.
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- Enable control access to end-of-life and/or experimental APIs.
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Note that API versioning and software versioning are only indirectly related. The [API and release
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The JSON and Protobuf serialization schemas follow the same guidelines for schema changes. The following descriptions cover both formats.
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**Note:** the API versioning and software versioning are indirectly related. The [API and release
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versioning proposal](https://git.k8s.io/community/contributors/design-proposals/release/versioning.md) describes the relationship between API versioning and software versioning.
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{: .note}
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Different API versions imply different levels of stability and support. The criteria for each level are described
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in more detail in the [API Changes documentation](https://git.k8s.io/community/contributors/devel/api_changes.md#alpha-beta-and-stable-versions).
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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](https://git.k8s.io/community/contributors/devel/api_changes.md#alpha-beta-and-stable-versions).
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The criteria are summarized here:
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- Alpha level:
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Here's a summary of each level:
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- Alpha:
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- The version names contain `alpha` (for example, `v1alpha1`).
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- The software may contain bugs. Enabling a feature may expose bugs. A feature may be disabled by default.
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- The software may contain bugs. Enabling a feature may expose bugs. A feature may be disabled by default.
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- The support for a feature may be dropped at any time without notice.
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- The API may change in incompatible ways in a later software release without notice.
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- The software is recommended for use only in short-lived testing clusters, due to increased risk of bugs and lack of long-term support.
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- Beta level:
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- The software is recommended for use only in short-lived testing clusters, due to increased risk of bugs and lack of long-term support.
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- Beta:
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- The version names contain `beta` (for example, `v2beta3`).
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- The software is well tested. Enabling a feature is considered safe. Features are enabled by default.
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- The software is well tested. Enabling a feature is considered safe. Features are enabled by default.
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- The support for a feature will not be dropped, though the details may change.
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- The schema and/or semantics of objects may change in incompatible ways in a subsequent beta or stable release. When this happens, migration instructions will be provided. This may require deleting, editing, and re-creating
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- 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. This may require deleting, editing, and re-creating
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API objects. The editing process may require some thought. This may require downtime for applications that rely on the feature.
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- The software is recommended for only non-business-critical uses because of potential for incompatible changes in subsequent releases. If you have multiple clusters which can be upgraded independently, you may be able to relax this restriction.
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- **Please try our beta features and give feedback on them! Once they exit beta, it may not be practical for us to make more changes.**
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- Stable level:
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- The software is recommended for only non-business-critical uses because of potential for incompatible changes in subsequent releases. If you have multiple clusters which can be upgraded independently, you may be able to relax this restriction.
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**Note:** Try the beta features and provide feedback. After the features exit beta, it may not be practical to make more changes.
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{: .note}
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- Stable:
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- The version name is `vX` where `X` is an integer.
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- The stable versions of features will appear in released software for many subsequent versions.
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- The stable versions of features appear in released software for many subsequent versions.
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## API groups
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@ -66,26 +73,26 @@ Currently, there are several API groups in use:
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* The *core* (also called *legacy*) group, which is at REST path `/api/v1` and is not specified as part of the `apiVersion` field, for example, `apiVersion: v1`.
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* The named groups are at REST path `/apis/$GROUP_NAME/$VERSION`, and use `apiVersion: $GROUP_NAME/$VERSION`
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(for example, `apiVersion: batch/v1`). Full list of supported API groups can be seen in [Kubernetes API reference](/docs/reference/).
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(for example, `apiVersion: batch/v1`). You can find the full list of supported API groups in [Kubernetes API reference](/docs/reference/).
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There are two supported paths to extending the API with [custom resources](/docs/concepts/api-extension/custom-resources/):
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The two paths that support extending the API with [custom resources](/docs/concepts/api-extension/custom-resources/) are:
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1. [CustomResourceDefinition](/docs/tasks/access-kubernetes-api/extend-api-custom-resource-definitions/)
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is for users with very basic CRUD needs.
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1. Coming soon: users needing the full set of Kubernetes API semantics can implement their own apiserver
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and use the [aggregator](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/aggregated-api-servers.md)
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to make it seamless for clients.
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- [CustomResourceDefinition](/docs/tasks/access-kubernetes-api/extend-api-custom-resource-definitions/)
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for basic CRUD needs.
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- [aggregator](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/aggregated-api-servers.md) for a full set of Kubernetes API semantics to implement their own apiserver.
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## Enabling API groups
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Certain resources and API groups are enabled by default. You can enable or disable them by setting `--runtime-config`
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on apiserver. `--runtime-config` accepts comma separated values. For example, to disable batch/v1, set
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`--runtime-config=batch/v1=false`, to enable batch/v2alpha1, set `--runtime-config=batch/v2alpha1`.
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Certain resources and API groups are enabled by default. You can enable or disable them by setting `--runtime-config`
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on the apiserver. `--runtime-config` accepts comma separated values. For example:
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- to disable batch/v1, set `--runtime-config=batch/v1=false`
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- to enable batch/v2alpha1, set `--runtime-config=batch/v2alpha1`
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The flag accepts comma separated set of key=value pairs describing runtime configuration of the apiserver.
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IMPORTANT: Enabling or disabling groups or resources requires restarting apiserver and controller-manager
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**Note:** When you enable or disable groups or resources, you need to restart the apiserver and controller-manager
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to pick up the `--runtime-config` changes.
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{: .note}
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## Enabling resources in the groups
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