User-specified readiness probes with periodSeconds>0 should not be ignored

[julz]

What version of Knative?

all recent ones

Expected Behavior

setting a readinessprobe with period>0 should cause the container's readiness to be probed at the requested frequency for the life of the container

Actual Behavior

the probe is ignored after startup. See https://github.com/knative/serving/blob/master/pkg/queue/health/health_state.go#L87-L89.

Steps to Reproduce the Problem

1. ko apply -f https://github.com/julz/readybutnotsteady/blob/main/service.yaml
2. Wait for startup to succeed
3. curl readynotsteady.default.$domain/start-failing
4. See the pod never goes unready, even though the probe will now fail forever

[julz]

I don't think anyone thinks the current behaviour is correct, so I'm going to fix. I guess there's a question as to whether we need a feature flag for a release since it's technically backwards-incompatible to start doing this 🤔

/assign

[evankanderson]

/good-first-issue
/area autoscale
/triage accepted

[knative-prow-robot]

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Details

In response to this:

/good-first-issue
/area autoscale
/triage accepted

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.

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