https://bz.apache.org/bugzilla/show_bug.cgi?id=66302
Bug ID: 66302
Summary: Passing health check does not recover worker from its
error state
Product: Apache httpd-2
Version: 2.4-HEAD
Hardware: PC
OS: Linux
Status: NEW
Keywords: PatchAvailable
Severity: regression
Priority: P2
Component: mod_proxy_hcheck
Assignee: bugs@httpd.apache.org
Reporter: alessandro.cavali...@unibo.it
Target Milestone: ---
Created attachment 38407
--> https://bz.apache.org/bugzilla/attachment.cgi?id=38407&action=edit
mod_proxy_hcheck: recover worker from error state
While we were in the process of enabling mod_proxy_hcheck on some of our
apache2 nodes we encountered an unusual behavior: sometimes, after rebooting a
backend, its worker status remains marked as "Init Err" (balancer manager)
until another request is made to the backend, no matter how many health checks
complete successfully.
The following list shows the sequence of events leading to the problem:
1. Watchdog triggers health check, request is successful; worker status is
"Init Ok"
2. HTTP request to apache2 with unreachable backend (rebooting); status becomes
"Init Err"
3. Watchdog triggers another health check, request is again successful because
the backend recovered; worker status remains "Init Err"
4. same as 3
5. same as 4
The only way for the worker status to recover is to wait for "hcfails"
unsuccessful health checks and then again for "hcpasses" requests to be
completed or just wait for legitimate traffic to retry the failed worker, which
may not happen for a long time for rarely used applications.
This was surprising to us since we were expecting the worker status to be
recovered after "hcpasses" successful health checks; however this doesn't seem
to happen when the error status is triggered by ordinary traffic to the backend
(i.e not health checks).
We believe this behavior was accidentally introduced in r1725523. The patch we
are proposing seems to fix the problem in our environment.
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