[WIP] Add a flag to QueueProxy to enable reporting the request latency in header

[lichenran1234]

[WIP] Add a flag to QueueProxy to enable reporting the request latency in header

Proposed Changes

Add a flag to QueueProxy to enable reporting the request_latency/app_request_latency in the response header. They are already emitted by QueueProxy as Prometheus metrics:

• app_request_latency is user container latency
• request_latency is user container latency + queue latency

Some Knative users run Knative with an extra layer on top of the Knative networking layer, so the architecture looks like: extra layer (could be a custom load balancer) -> Knative networking layer -> Knative activator -> QueueProxy -> user container

With this change, those users can measure the latency between their custom load balancer and QueueProxy (i.e. the additional overhead imposed by their system).

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[linux-foundation-easycla[bot]]

• :x: - login: @lichenran1234 / name: Chenran Li . The commit (151655b4727f2e1af8c762b07412e20a4f879547, bd2f26458d2021f31b8f21da98adc6a2299f3ba0, 9fb82965a757df7a3ba47ed0f6d341ca9ee1d9dc, 604e61a9639cdebf7ebfe2b410ab3f0fa01e7a27, 257030fc3a02c6a7d98df5575e4fe3509ec16049, 56521caf41b4ca5b30b50d10a6f409ce3beeb065, 65b9b542248da5cd9f4153b3c97f440eeee10954, 62e1512d2ed75bad05a7f62587e0a4ee113c2b6c) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

[knative-prow[bot]]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: lichenran1234 To complete the pull request process, please assign nak3 after the PR has been reviewed. You can assign the PR to them by writing /assign @nak3 in a comment when ready.

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[knative-prow[bot]]

Hi @lichenran1234. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[knative-prow-robot]

@lichenran1234: PR needs rebase.

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[nader-ziada]

@dprotaso should this PR be closed as well based on closing the issue for inactivity - https://github.com/knative/serving/issues/12908#issuecomment-1203086546

[github-actions[bot]]

This Pull Request is stale because it has been open for 90 days with no activity. It will automatically close after 30 more days of inactivity. Reopen with /reopen. Mark as fresh by adding the comment /remove-lifecycle stale.

[dprotaso]

@dprotaso should this PR be closed as well based on closing the issue for inactivity - #12908 (comment)