kube-proxy service health: add new header with number of local endpoints

[cezarygerard]

/kind feature

What this PR does / why we need it:

• add new header "X-Load-Balancing-Endpoint-Weight" returned from service health. Value of the header is number of local endpoints. Header can be used in weighted load balancing. Parsing header for number of endpoints is faster than unmarshalling json from the content body.

• add missing unit test for new and old headers returned from service health

Special notes for your reviewer:

I am happy to discuss this on SIG Network meeting

Does this PR introduce a user-facing change?

yes, to some extend
kube-proxy service health will return additional http header "X-Load-Balancing-Endpoint-Weight" with number of local endpoints.
no action is required from users

kube-proxy service health returns http header "X-Load-Balancing-Endpoint-Weight" with number of local endpoints. The same information is still available in response body JSON payload.LocalEndpoints.

[k8s-ci-robot]

This issue is currently awaiting triage.

If a SIG or subproject determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

The triage/accepted label can be added by org members by writing /triage accepted in a comment.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[aojea]

/assign @thockin @danwinship @khenidak

I talked with Cezary offline about this, and the header seems generic enough and not used anywhere that all new implementations can benefit from it.

It LGTM but waiting for others to have consensus

[thockin]

I'm OK with this, but open to discussion. We could add a flag to set the header name, but I'd only do that if we have a concrete use-case.

We would want other proxier implementations to adopt this, too, right? Cilium, Antrea, ... who else? @rikatz

Can you bring this to sig-net in an upcoming meeting?

[rikatz]

should mark @tgraf @antoninbas and probably @caseydavenport for the proxiers of each CNI :)

[danwinship]

The HealthCheckNodePort check returns a JSON result. We could add this there.
We already include this there:

fmt.Fprint(resp, strings.Trim(dedent.Dedent(fmt.Sprintf(`
	{
		"service": {
			"namespace": %q,
			"name": %q
		},
		"localEndpoints": %d,
		"serviceProxyHealthy": %v
	}
	`, h.name.Namespace, h.name.Name, count, kubeProxyHealthy)), "\n"))

[cezarygerard]

@danwinship

I know the value from the header can already be parsed out from the body
but header is easier to parse for Load Balancers

[cezarygerard]

One more use case suggested by @thockin is HTTP HEAD method that can be used to check the health.

Current implementation of the service healthchecks supports the HEAD method, I guess this comes for free with "net/http" implementation.

Example from my k8s node:

$curl --head localhost:32478

HTTP/1.1 200 OK
Content-Type: application/json
X-Content-Type-Options: nosniff
Date: Thu, 06 Jul 2023 16:47:07 GMT
Content-Length: 104

[cezarygerard]

@danwinship

added draft PR with documentation update to https://kubernetes.io/docs/concepts/services-networking/service/

kubernetes/website#41926

[thockin]

Thanks!

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 8daa96f2294288354ad2d26baea4272cef690287

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cezarygerard, thockin

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• pkg/proxy/OWNERS [thockin]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment