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From Alex Bligh <a...@alex.org.uk>
Subject [users@httpd] Reverse proxy ap_get_scoreboard_lb(0) failed + seg fault
Date Wed, 27 Jun 2012 12:39:54 GMT
I am occasionally seeing a seg fault and/or "ap_get_scoreboard_lb(%d) failed
in child" in logs in apache on one particular instance of our software (see
anonymised example below).

This should be on:
 apache2-mpm-prefork 2.2.14-5ubuntu8.7
or similar (I am checking).

This occurs after doing a 'reload' on apache, then trying to use the
a site with a reverse proxy (relevant lines of config appended).

I note this bug:
 https://issues.apache.org/bugzilla/show_bug.cgi?id=41729

which does not contain the seg fault, but seems similar. There is apparently
and issue with graceful reload of apache and scoreboard maintenance for the
reverse proxy. Google suggests others are having similar issues.

Any ideas:

1. How to get around this, without doing a stop/start every time rather than
   a reload, which is undesirable (we have automated processes triggering
   a reload)?

2. How to detect when it has got into this state?

3. Why it might be affecting one particular customer of ours, and not
   the rest of the world?

-- 
Alex Bligh

[Thu Jun 21 15:29:42 2012] [notice] child pid 17313 exit signal 
Segmentation fault (11)
[Thu Jun 21 15:29:43 2012] [notice] child pid 17317 exit signal 
Segmentation fault (11)
[Thu Jun 21 15:29:43 2012] [error] proxy: ap_get_scoreboard_lb(2) failed in 
child 17404 for worker proxy:reverse
[Thu Jun 21 15:29:43 2012] [error] proxy: ap_get_scoreboard_lb(0) failed in 
child 17404 for worker http://192.200.0.2:1234/admin/
[Thu Jun 21 15:29:43 2012] [error] proxy: ap_get_scoreboard_lb(1) failed in 
child 17404 for worker http://192.200.0.2:1234/user/
[Thu Jun 21 15:29:44 2012] [notice] child pid 17316 exit signal 
Segmentation fault (11)
[Thu Jun 21 15:29:44 2012] [error] proxy: ap_get_scoreboard_lb(2) failed in 
child 17408 for worker proxy:reverse
[Thu Jun 21 15:29:44 2012] [error] proxy: ap_get_scoreboard_lb(2) failed in 
child 17407 for worker proxy:reverse
[Thu Jun 21 15:29:44 2012] [error] proxy: ap_get_scoreboard_lb(0) failed in 
child 17408 for worker http://192.200.0.2:1234/admin/
[Thu Jun 21 15:29:44 2012] [error] proxy: ap_get_scoreboard_lb(0) failed in 
child 17407 for worker http://192.200.0.2:1234/admin/
[Thu Jun 21 15:29:44 2012] [error] proxy: ap_get_scoreboard_lb(1) failed in 
child 17408 for worker http://192.200.0.2:1234/user/
[Thu Jun 21 15:29:44 2012] [error] proxy: ap_get_scoreboard_lb(1) failed in 
child 17407 for worker http://192.200.0.2:1234/user/
[Thu Jun 21 15:29:45 2012] [notice] child pid 17322 exit signal 
Segmentation fault (11)
[Thu Jun 21 15:29:46 2012] [notice] child pid 17326 exit signal 
Segmentation fault (11)
[Thu Jun 21 15:29:46 2012] [error] proxy: ap_get_scoreboard_lb(2) failed in 
child 17413 for worker proxy:reverse
[Thu Jun 21 15:29:46 2012] [error] proxy: ap_get_scoreboard_lb(0) failed in 
child 17413 for worker http://192.200.0.2:1234/admin/
[Thu Jun 21 15:29:46 2012] [error] proxy: ap_get_scoreboard_lb(1) failed in 
child 17413 for worker http://192.200.0.2:1234/user/



Listen 192.200.0.1:4443
<VirtualHost 192.200.0.1:4443>
        <Proxy *>
                AddDefaultCharset off
                Order deny,allow
                Allow from all
        </Proxy>

        ServerAdmin noone@example.com
        ServerName 192.200.0.1
...
        SSLEngine on
...
        # Let apache correctly rewrite redirect
        ProxyPass / http://192.200.0.2:1234/admin/ timeout=30 
connectiontimeout=30 retry=10
        ProxyPassReverse / http://192.200.0.2:1234/admin/
        ProxyTimeout 30

        # Let apache pass the original host not the ProxyPass one
        ProxyPreserveHost On
....

</VirtualHost>



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