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Remove duplicated content in concepts and reference

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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.
This commit is contained in:
Qiming Teng
2020-09-14 10:41:23 +08:00
parent ba3c2c4b29
commit 3cc1371651
2 changed files with 114 additions and 153 deletions
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content/en/docs/reference/using-api/api-overview.md
+64 -59
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@@ -18,95 +18,100 @@ This page provides an overview of the Kubernetes API.
<!-- body -->
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
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](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/).
Most operations can be performed through the
[kubectl](/docs/reference/kubectl/overview/) command-line interface or other
command-line tools, such as [kubeadm](/docs/reference/setup-tools/kubeadm/kubeadm/), which in turn use
the API. However, you can also access the API directly using REST calls.
Consider using one of the [client libraries](/docs/reference/using-api/client-libraries/)
if you are writing an application using the Kubernetes API.
## API versioning
To eliminate fields or restructure resource representations, Kubernetes supports
multiple API versions, each at a different API path. For example: `/api/v1` or
`/apis/rbac.authorization.k8s.io/v1alpha1`.
The JSON and Protobuf serialization schemas follow the same guidelines for
schema changes. The following descriptions cover both formats.
The version is set at the API level rather than at the resource or field level to:
The API versioning and software versioning are indirectly related.
The [API and release versioning proposal](https://git.k8s.io/community/contributors/design-proposals/release/versioning.md)
describes the relationship between API versioning and software versioning.
- Ensure that the API presents a clear and consistent view of system resources and behavior.
- Enable control access to deprecated or experimental APIs.
The JSON and Protobuf serialization schemas follow the same guidelines for schema changes. The following descriptions cover both formats.
{{< note >}}
The API versioning and software versioning are indirectly related. The [API and release
versioning proposal](https://git.k8s.io/community/contributors/design-proposals/release/versioning.md) describes the relationship between API versioning and software versioning.
{{< /note >}}
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).
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).
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 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.
- 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 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 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,
or recreating API objects. The editing process may not be straightforward. 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.
- Try the beta features and provide feedback. After the features exit beta, it may not be practical
to make more changes.
- 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 >}}
Try the beta features and provide feedback. After the features exit beta, it
may not be practical to make more changes.
{{< /note >}}
- 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](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.
[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.
Currently, there are several API groups in use:
- 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](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/).
* 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](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/).
The two paths that support extending the API with [custom resources](/docs/concepts/extend-kubernetes/api-extension/custom-resources/) are:
## Enabling or disabling API groups {#enabling-or-disabling}
- [CustomResourceDefinition](/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/)
for basic CRUD needs.
- [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.
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. For example:
## 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. For example:
- to disable batch/v1, set `--runtime-config=batch/v1=false`
- to enable batch/v2alpha1, set `--runtime-config=batch/v2alpha1`
- 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.
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.
{{< /note >}}
## Persistence
Kubernetes stores its serialized state in terms of the API resources by writing them into
{{< glossary_tooltip term_id="etcd" >}}.
## {{% heading "whatsnext" %}}
- Learn more about [API conventions](https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#api-conventions)
- Read the design documentation for
[aggregator](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/api-machinery/aggregated-api-servers.md)