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community/contributors/devel/adding-an-APIGroup.md

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Adding an API Group

This document includes the steps to add an API group. You may also want to take a look at PR #16621 and PR #13146, which add API groups.

Please also read about API conventions and API changes before adding an API group.

Your core group package:

We plan on improving the way the types are factored in the future; see #16062 for the directions in which this might evolve.

  1. Create a folder in pkg/apis to hold your group. Create types.go in pkg/apis/<group>/ and pkg/apis/<group>/<version>/ to define API objects in your group;

  2. Create pkg/apis/<group>/{register.go, <version>/register.go} to register this group's API objects to the encoding/decoding scheme (e.g., pkg/apis/authentication/register.go and pkg/apis/authentication/v1beta1/register.go; The register files must have a var called SchemeBuilder for the generated code to reference. There must be an AddToScheme method for the installer to reference. You can look at a group under pkg/apis/... for example register.go files to use as a template, but do not copy the register.go files under pkg/api/...--they are not general.

  3. Add a pkg/apis/<group>/install/install.go, You probably only need to change the name of group and version in the example). This package must be imported by the server along with k8s.io/kubernetes/pkg/api/install. Import these packages with the blank identifier as they do not have user callable code and exist solely for their initialization side-effects.

Step 2 and 3 are mechanical, we plan on autogenerate these using the cmd/libs/go2idl/ tool.

Type definitions in types.go

Each type should be an exported struct (have a capitalized name). The struct should have the TypeMeta and ObjectMeta embeds. There should be a Spec and a Status field. If the object is solely a data storage object, and will not be modified by a controller, the status field can be left off and the fields inside the Spec can be inlined directly into the struct.

For each top-level type there should also be a List struct. The List struct should have the TypeMeta and ListMeta embeds. There should be an Items field that is a slice of the defined type.

Scripts changes and auto-generated code:

  1. Generate conversions and deep-copies:

    1. Add your "group/" or "group/version" into cmd/libs/go2idl/conversion-gen/main.go;
    2. Make sure your pkg/apis/<group>/<version> directory has a doc.go file with the comment // +k8s:deepcopy-gen=package,register, to catch the attention of our generation tools.
    3. Make sure your pkg/apis/<group>/<version> directory has a doc.go file with the comment // +k8s:conversion-gen=<internal-pkg>, to catch the attention of our generation tools. For most APIs the only target you need is k8s.io/kubernetes/pkg/apis/<group> (your internal API).
    4. Make sure your pkg/apis/<group> and pkg/apis/<group>/<version> directories have a doc.go file with the comment +groupName=<group>.k8s.io, to correctly generate the DNS-suffixed group name.
    5. Run hack/update-all.sh.

  2. Generate files for Ugorji codec:

    1. Touch types.generated.go in pkg/apis/<group>{/, <version>};
    2. Run hack/update-codecgen.sh.

  3. Generate protobuf objects:

    1. Add your group to cmd/libs/go2idl/go-to-protobuf/protobuf/cmd.go to New() in the Packages field
    2. Run hack/update-generated-protobuf.sh

Client (optional):

We are overhauling pkg/client, so this section might be outdated; see #15730 for how the client package might evolve. Currently, to add your group to the client package, you need to:

  1. Create pkg/client/unversioned/<group>.go, define a group client interface and implement the client. You can take pkg/client/unversioned/extensions.go as a reference.

  2. Add the group client interface to the Interface in pkg/client/unversioned/client.go and add method to fetch the interface. Again, you can take how we add the Extensions group there as an example.

  3. If you need to support the group in kubectl, you'll also need to modify pkg/kubectl/cmd/util/factory.go.

Make the group/version selectable in unit tests (optional):

  1. Add your group in pkg/api/testapi/testapi.go, then you can access the group in tests through testapi.<group>;

  2. Add your "group/version" to KUBE_TEST_API_VERSIONS in hack/make-rules/test.sh and hack/make-rules/test-integration.sh

TODO: Add a troubleshooting section.

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