Throttler: CheckThrottlerResponseCode to replace HTTP status codes

[shlomi-noach]

Description

This PR adds CheckThrottlerResponseCode as a more formalized/standard response code to replace the existing HTTP response codes.

For now, and for v21, all checks return both HTTP response codes and CheckThrottlerResponseCode, and both are tested. Of course, v20 (and below) servers only return HTTP response codes.

In v22 or later we can get rid of the HTTP StatusCode fields used throughout the code and any associated functionality.

Related Issue(s)

• RFC: tablet throttler multi-metrics #15624 (comment) and RFC: tablet throttler multi-metrics #15624 (comment)
• Followup to Tablet throttler: multi-metric support #15988
• Documentation PR (required): Docs: throttler's response code replaces HTTP status website#1799

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[shlomi-noach]

Seeing Online DDL flow - Upgrade Downgrade Testing failures - converting to Draft while looking into it.

[codecov]

Codecov Report

Attention: Patch coverage is 72.63158% with 26 lines in your changes missing coverage. Please review.

Project coverage is 68.63%. Comparing base (e341f23) to head (d1a1039).

Files	Patch %	Lines
go/vt/vttablet/tabletmanager/rpc_throttler.go	0.00%	16 Missing ⚠️
.../vt/vttablet/tabletserver/throttle/check_result.go	89.74%	4 Missing ⚠️
go/vt/vttablet/tabletserver/tabletserver.go	0.00%	2 Missing ⚠️
go/vt/vttablet/tabletserver/throttle/check.go	92.30%	2 Missing ⚠️
go/vt/vttablet/tabletserver/throttle/throttler.go	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16491      +/-   ##
==========================================
+ Coverage   68.62%   68.63%   +0.01%     
==========================================
  Files        1551     1551              
  Lines      199515   199555      +40     
==========================================
+ Hits       136915   136970      +55     
+ Misses      62600    62585      -15     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[shlomi-noach]

Seeing Online DDL flow - Upgrade Downgrade Testing failures - converting to Draft while looking into it.

An unrelated artifact fetching error. Good to go.

[mattlord]

❤️

[mattlord]

Should this be an else if? I wouldn't think we'd want the http code to override the response code for the error, but maybe we do.

[shlomi-noach]

The two cpde blocks will behave identically. I intentionally separated to two separate ifs because for backwards compatibility sake, I must keep the old one, so adding as a separate block is "clean" diff-wise. In v22 we will remove that old one, and again the diff will be clean. WDYT?

[mattlord]

Sure, not a big deal at all.

[timvaillancourt]

🚀