[PR] Only restore a retried parent when the retry succeeds [trafficserver]

["masaori335 (via GitHub)" <gi...@apache.org>]

masaori335 opened a new pull request, #13474:
URL: https://github.com/apache/trafficserver/pull/13474

   A parent that accepts connections but never sends a response was marked down and then restored to the pool by the very next retry probe, even when that probe also failed, so it kept receiving traffic indefinitely while healthy peers took none of the load.
   
   handle_response_from_parent() called markParentUp() on entry, before the switch on current.state, so a parent selected as a retry candidate was restored before ATS knew the retry's outcome. markParentUp() zeroes failedAt and failCount; the markParentDown() that follows a failed probe then takes its result->retry branch, which leaves new_fail_count at 0, so available is never re-cleared. The parent therefore returned to the pool with a cleared failure count after every retry_time window, no matter how long it stayed degraded.
   
   The CONNECTION_ALIVE branch already calls markParentUp() for a retry that actually succeeded, which is the correct restore point. Removing the entry call restores the behavior that predates #8546: that commit backed out the retry-limiting work and replaced a retryComplete() call -- which only decremented an in-flight retry counter and never touched availability -- with markParentUp(), silently turning "the retry finished" into "the parent is healthy".
   
   Two autests pin both outcomes of the retry path. A parent that is still silent when probed stays down; a parent that has recovered is restored. Each was negative-controlled against its own call site: reverting this change fails the first, and removing the CONNECTION_ALIVE call fails only the second.


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Re: [PR] Only restore a retried parent when the retry succeeds [trafficserver]

["cmcfarlen (via GitHub)" <gi...@apache.org>]

cmcfarlen commented on PR #13474:
URL: https://github.com/apache/trafficserver/pull/13474#issuecomment-5207867798

   Cherry-picked to the 10.2.x branch as a403974a7664b071e3b1c2ac4f3af6ea11f4207b for the 10.2.0 release.


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Re: [PR] Only restore a retried parent when the retry succeeds [trafficserver]

["masaori335 (via GitHub)" <gi...@apache.org>]

masaori335 merged PR #13474:
URL: https://github.com/apache/trafficserver/pull/13474


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