Add ability to skip OpenAPI handler installation

[kevindelgado]

What type of PR is this?

/kind bug

What this PR does / why we need it:

This provides the ability to configure a GenericAPIServer to not install the OpenAPI handler so that the kube-aggregator (which has its own OpenAPI handler) does not double register the openapi/v2 handler.

Which issue(s) this PR fixes:

Addresses #99046 (comment)

Does this PR introduce a user-facing change?

NONE

[kevindelgado]

/assign @liggitt

[kevindelgado]

cc @apelisse

[kevindelgado]

Thinking about Anotine's feedback about not wanting to store a bool another idea I have is to require consumers to set the StaticOpenAPISpec on the generic config themselves at the same time they set the OpenAPIConfig. This would require adding the spec to the generic config struct.

Then, the handler installation is triggered by the spec being non-nil rather than the config. Instead of calling routes.OpenAPI#Install which creates a spec to then install the handler, we install the handler directly from the provided spec.

The end result is that GenericAPIServer's StaticOpenAPISpec is only used for openAPI handler installation while the openAPIConfig is only used for generating openAPI models (which is in turn used by the field manager).

This seems like a better approach in terms of decoupling the OpenAPIConfig and StaticOpenAPISpec as long as we're okay with requiring the consumer to be the one to generate the spec from the config (if they want the handler installed).

Let me know what you think @liggitt @apelisse

[kevindelgado]

Okay, I just spoke to @apelisse and we decided to continue with the boolean approach. My suggestion about requiring consumers to pass the spec could introduce a big foot-gun where the spec doesn't match the config and so we'd probably need to generate the spec anyways to check for that.

Other ideas like passing a function in the config to optionally convert to a spec seemed like overkill compared to the bool, so we've agreed on that for now. Thoughts? PTAL @liggitt

[liggitt]

yeah, this seems reasonable

/lgtm
/approve
/ok-to-test

[liggitt]

/milestone v1.21
/kind bug

avoids a spurious stack trace in the API server log on every start as a regression in 1.21

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kevindelgado, liggitt

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Needs approval from an approver in each of these files:

• cmd/kube-apiserver/OWNERS [liggitt]
• staging/src/k8s.io/apiserver/OWNERS [liggitt]
• staging/src/k8s.io/kube-aggregator/OWNERS [liggitt]

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[kevindelgado]

Can you give it another lgtm @liggitt, I had to change the name of the config in server/start (s/genericConfig/serverConfig). All tests passing now.

[liggitt]

/lgtm

[kevindelgado]

/retest