Remove duplicated content in concepts and reference
We currently have quite some contents duplicated between the concepts and the reference section, which is not good. This PR is an effort to remove the duplicated content from the two pages while providing links for readers to check the reference easily.pull/23866/head
Qiming Teng
parent
ba3c2c4b29
commit
3cc1371651
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@ -16,30 +16,23 @@ card:
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The core of Kubernetes' {{< glossary_tooltip text="control plane" term_id="control-plane" >}}
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is the {{< glossary_tooltip text="API server" term_id="kube-apiserver" >}}. The API server
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exposes an HTTP API that lets end users, different parts of your cluster, and external components
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communicate with one another.
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exposes an HTTP API that lets end users, different parts of your cluster, and
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external components communicate with one another.
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The Kubernetes API lets you query and manipulate the state of objects in the Kubernetes API
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(for example: Pods, Namespaces, ConfigMaps, and Events).
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API endpoints, resource types and samples are described in the [API Reference](/docs/reference/kubernetes-api/).
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Most operations can be performed through the
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[kubectl](/docs/reference/kubectl/overview/) command-line interface or other
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command-line tools, such as
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[kubeadm](/docs/reference/setup-tools/kubeadm/kubeadm/), which in turn use the
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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/using-api/client-libraries/)
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if you are writing an application using the Kubernetes API.
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<!-- body -->
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## API changes
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Any system that is successful needs to grow and change as new use cases emerge or existing ones change.
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Therefore, Kubernetes has design features to allow the Kubernetes API to continuously change and grow.
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The Kubernetes project aims to _not_ break compatibility with existing clients, and to maintain that
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compatibility for a length of time so that other projects have an opportunity to adapt.
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In general, new API resources and new resource fields can be added often and frequently.
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Elimination of resources or fields requires following the
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[API deprecation policy](/docs/reference/using-api/deprecation-policy/).
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What constitutes a compatible change, and how to change the API, are detailed in
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[API changes](https://git.k8s.io/community/contributors/devel/sig-architecture/api_changes.md#readme).
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## OpenAPI specification {#api-specification}
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Complete API details are documented using [OpenAPI](https://www.openapis.org/).
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@ -78,95 +71,58 @@ You can request the response format using request headers as follows:
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<caption>Valid request header values for OpenAPI v2 queries</caption>
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</table>
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Kubernetes implements an alternative Protobuf based serialization format for the API that is primarily intended for intra-cluster communication, documented in the [design proposal](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/protobuf.md) and the IDL files for each schema are located in the Go packages that define the API objects.
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Kubernetes implements an alternative Protobuf based serialization format that
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is primarily intended for intra-cluster communication. For more information
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about this format, see the [Kubernetes Protobuf serialization](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/protobuf.md) design proposal and the
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Interface Definition Language (IDL) files for each schema located in the Go
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packages that define the API objects.
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## API versioning
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## API changes
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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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`/apis/rbac.authorization.k8s.io/v1alpha1`.
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Any system that is successful needs to grow and change as new use cases emerge or existing ones change.
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Therefore, Kubernetes has designed its features to allow the Kubernetes API to continuously change and grow.
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The Kubernetes project aims to _not_ break compatibility with existing clients, and to maintain that
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compatibility for a length of time so that other projects have an opportunity to adapt.
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Versioning is done at the API level rather than at the resource or field level to ensure that the
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API presents a clear, consistent view of system resources and behavior, and to enable controlling
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access to end-of-life and/or experimental APIs.
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In general, new API resources and new resource fields can be added often and frequently.
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Elimination of resources or fields requires following the
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[API deprecation policy](/docs/reference/using-api/deprecation-policy/).
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The JSON and Protobuf serialization schemas follow the same guidelines for schema changes - all descriptions below cover both formats.
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What constitutes a compatible change, and how to change the API, are detailed in
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[API changes](https://git.k8s.io/community/contributors/devel/sig-architecture/api_changes.md#readme).
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Note that API versioning and Software versioning are only indirectly related. The
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[Kubernetes Release Versioning](https://git.k8s.io/community/contributors/design-proposals/release/versioning.md)
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proposal describes the relationship between API versioning and software versioning.
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## API groups and versioning
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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
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[API Changes](https://git.k8s.io/community/contributors/devel/sig-architecture/api_changes.md#alpha-beta-and-stable-versions)
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documentation. They are summarized here:
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To make it easier to eliminate fields or restructure resource representations,
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Kubernetes supports multiple API versions, each at a different API path, such
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as `/api/v1` or `/apis/rbac.authorization.k8s.io/v1alpha1`.
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- Alpha level:
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- The version names contain `alpha` (e.g. `v1alpha1`).
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- May be buggy. Enabling the feature may expose bugs. Disabled by default.
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- Support for 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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- 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 version names contain `beta` (e.g. `v2beta3`).
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- Code is well tested. Enabling the feature is considered safe. Enabled by default.
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- Support for the overall feature will not be dropped, though 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,
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we will provide instructions for migrating to the next version. 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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- Recommended for only non-business-critical uses because of potential for incompatible changes in subsequent releases. If you have
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multiple clusters which can be upgraded independently, you may be able to relax this restriction.
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- **Please do 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 version name is `vX` where `X` is an integer.
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- Stable versions of features will appear in released software for many subsequent versions.
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Versioning is done at the API level rather than at the resource or field level
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to ensure that the API presents a clear, consistent view of system resources
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and behavior, and to enable controlling access to end-of-life and/or
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experimental APIs.
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## API groups
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Refer to [API versions reference](/docs/reference/using-api/api-overview/#api-versioning)
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for more details on the API version level definitions.
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To make it easier to extend its API, Kubernetes implements [*API groups*](https://git.k8s.io/community/contributors/design-proposals/api-machinery/api-group.md).
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The API group is specified in a REST path and in the `apiVersion` field of a serialized object.
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To make it easier to evolve and to extend its API, Kubernetes implements
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[API groups](/docs/reference/using-api/api-overview/#api-groups) that can be
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[enabled or disabled](/docs/reference/using-api/api-overview/#enabling-or-disabling).
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There are several API groups in a cluster:
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## API Extension
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1. The *core* group, also referred to as the *legacy* group, is at the REST path `/api/v1` and uses `apiVersion: v1`.
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1. *Named* groups are at REST path `/apis/$GROUP_NAME/$VERSION`, and use `apiVersion: $GROUP_NAME/$VERSION`
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(e.g. `apiVersion: batch/v1`). The Kubernetes [API reference](/docs/reference/kubernetes-api/) has a
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full list of available API groups.
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There are two paths to extending the API with [custom resources](/docs/concepts/extend-kubernetes/api-extension/custom-resources/):
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1. [CustomResourceDefinition](/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/)
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lets you declaratively define how the API server should provide your chosen resource API.
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1. You can also [implement your own extension API server](/docs/tasks/extend-kubernetes/setup-extension-api-server/)
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and use the [aggregator](/docs/tasks/extend-kubernetes/configure-aggregation-layer/)
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to make it seamless for clients.
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## Enabling or disabling API groups
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Certain resources and API groups are enabled by default. They can be enabled or disabled by setting `--runtime-config`
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as a command line option to the kube-apiserver.
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`--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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The flag accepts comma separated set of key=value pairs describing runtime configuration of the API server.
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{{< note >}}Enabling or disabling groups or resources requires restarting the kube-apiserver and the
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kube-controller-manager to pick up the `--runtime-config` changes.{{< /note >}}
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## Persistence
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Kubernetes stores its serialized state in terms of the API resources by writing them into
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{{< glossary_tooltip term_id="etcd" >}}.
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The Kubernetes API can be extended in one of two ways:
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1. [Custom resources](/docs/concepts/extend-kubernetes/api-extension/custom-resources/)
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let you declaratively define how the API server should provide your chosen resource API.
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1. You can also extend the Kubernetes API by implementing an
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[aggregation layer](/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/).
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## {{% heading "whatsnext" %}}
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[Controlling API Access](/docs/reference/access-authn-authz/controlling-access/) describes
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how the cluster manages authentication and authorization for API access.
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Overall API conventions are described in the
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[API conventions](https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#api-conventions)
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document.
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API endpoints, resource types and samples are described in the [API Reference](/docs/reference/kubernetes-api/).
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- Learn how to extend the Kubernetes API by adding your own
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[CustomResourceDefinition](/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/).
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- [Controlling API Access](/docs/reference/access-authn-authz/controlling-access/) describes
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how the cluster manages authentication and authorization for API access.
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- Learn about API endpoints, resource types and samples by reading
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[API Reference](/docs/reference/kubernetes-api/).
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@ -18,95 +18,100 @@ This page provides an overview of the Kubernetes API.
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<!-- body -->
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The REST API is the fundamental fabric of Kubernetes. All operations and communications between components
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and external user commands are REST API calls that the API Server handles. Consequently, everything in the Kubernetes
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The REST API is the fundamental fabric of Kubernetes. All operations and
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communications between components, and external user commands are REST API
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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/{{< param "version" >}}/).
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Most operations can be performed through the
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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/using-api/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 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/rbac.authorization.k8s.io/v1alpha1`.
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The JSON and Protobuf serialization schemas follow the same guidelines for
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schema changes. The following descriptions 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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The API versioning and software versioning are indirectly related.
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The [API and release versioning proposal](https://git.k8s.io/community/contributors/design-proposals/release/versioning.md)
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describes the relationship between API versioning and software versioning.
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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 deprecated or experimental APIs.
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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 >}}
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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 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/sig-architecture/api_changes.md#alpha-beta-and-stable-versions).
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Different API versions indicate different levels of stability and support. You
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can find more information about the criteria for each level in the
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[API Changes documentation](https://git.k8s.io/community/contributors/devel/sig-architecture/api_changes.md#alpha-beta-and-stable-versions).
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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
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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
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and lack of long-term support.
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- The software is recommended for use only in short-lived testing clusters,
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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.
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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 or semantics of objects may change in incompatible ways in a subsequent beta or stable release.
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When this happens, migration instructions are provided. Schema changes may require deleting, editing,
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or recreating API objects. The editing process may not be straightforward. Migration may require
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downtime for applications that rely on the feature.
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- The software is not recommended for production uses. Subsequent releases may introduce
|
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incompatible changes. If you have multiple clusters which can be upgraded independently,
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you may be able to relax this restriction.
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- Try the beta features and provide feedback. After the features exit beta, it may not be practical
|
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to make more changes.
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|
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- The schema and/or semantics of objects may change in incompatible ways in
|
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a subsequent beta or stable release. When this happens, migration
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instructions are provided. Schema changes may require deleting, editing, and
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re-creating API objects. The editing process may not be straightforward.
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The migration may require downtime for applications that rely on the feature.
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- The software is not recommended for production uses. Subsequent releases
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may introduce incompatible changes. If you have multiple clusters which
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can be upgraded independently, you may be able to relax this restriction.
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{{< note >}}
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Try the beta features and provide feedback. After the features exit beta, it
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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 appear in released software for many subsequent versions.
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## API groups
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[API groups](https://git.k8s.io/community/contributors/design-proposals/api-machinery/api-group.md) 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.
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[API groups](https://git.k8s.io/community/contributors/design-proposals/api-machinery/api-group.md)
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make it easier to extend the Kubernetes API.
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The API group is specified in a REST path and in the `apiVersion` field of a
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serialized object.
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Currently, there are several API groups in use:
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- The *core* (also called *legacy*) group is found at REST path `/api/v1`. The core group is not specified
|
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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`). You can find the full list of supported API groups in
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[Kubernetes API reference](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/).
|
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* The *core* (also called *legacy*) group is found at REST path `/api/v1`.
|
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The core group is not specified as part of the `apiVersion` field, for
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example, `apiVersion: v1`.
|
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* The named groups are at REST path `/apis/$GROUP_NAME/$VERSION` and use
|
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`apiVersion: $GROUP_NAME/$VERSION` (for example, `apiVersion: batch/v1`).
|
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You can find the full list of supported API groups in
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[Kubernetes API reference](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/).
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The two paths that support extending the API with [custom resources](/docs/concepts/extend-kubernetes/api-extension/custom-resources/) are:
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## Enabling or disabling API groups {#enabling-or-disabling}
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- [CustomResourceDefinition](/docs/tasks/extend-kubernetes/custom-resources/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 API server.
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Certain resources and API groups are enabled by default. You can enable or
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disable them by setting `--runtime-config` on the API server. The
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`--runtime-config` flag accepts comma separated `<key>=<value>` pairs
|
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describing the runtime configuration of the API server. For example:
|
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|
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## Enabling or disabling API groups
|
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|
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Certain resources and API groups are enabled by default. You can enable or disable them by
|
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setting `--runtime-config` on the API server. The `--runtime-config` flag accepts comma separated
|
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key=value pairs describing the runtime configuration of the API server. For example:
|
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|
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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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- 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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|
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{{< note >}}
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When you enable or disable groups or resources, you need to restart the API server and controller-manager
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to pick up the `--runtime-config` changes.
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When you enable or disable groups or resources, you need to restart the API
|
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server and controller manager to pick up the `--runtime-config` changes.
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{{< /note >}}
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## Persistence
|
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|
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Kubernetes stores its serialized state in terms of the API resources by writing them into
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{{< glossary_tooltip term_id="etcd" >}}.
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## {{% heading "whatsnext" %}}
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- Learn more about [API conventions](https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#api-conventions)
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- Read the design documentation for
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[aggregator](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/aggregated-api-servers.md)
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|
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