[request-tracker-maintainers] Bug#595054: Bug#595054: request-tracker3.8: Race condition between RT3.8+apache2 and MySQL when booting by insserv

[Matt Zagrabelny]

On Tue, Aug 31, 2010 at 3:39 PM, Dominic Hargreaves <dom at earth.li> wrote:
> On Tue, Aug 31, 2010 at 10:17:34PM +0400, Konstantin Khomoutov wrote:
>> I'm using RT 3.8 with apache2 via mod_perl, MySQL is used as a database
>> backend. When the server is booted using insserv, apache2 starts long
>> before MySQL and for some reason some bit of RT tries to access the
>> MySQL server, times out and fails; this prevents apache2 from starting.
>
> [snip logs]
>
>> DBI connect('dbname=rtdb;host=localhost','rtuser',...) failed: Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2) at /usr/share/perl5/DBIx/SearchBuilder/Handle.pm line 106
>> [Tue Aug 31 21:40:18 2010] [error] Connect Failed Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)\n at /usr/share/request-tracker3.8/lib/RT.pm line 217\nCompilation failed in require at (eval 2) line 1.\n
>> [Tue Aug 31 21:40:18 2010] [error] Can't load Perl file: /usr/share/request-tracker3.8/libexec/webmux.pl for server rt-admin.domain007.com:0, exiting...
>>
>> If I then start apache2 by hand, it starts OK (it only complains about
>> the RTAddressRegexp config variable being unset which is harmless I suppose).
>
> [snip details]
>
>> I suspect the included "/etc/request-tracker3.8/apache2-modperl2.conf"
>> file might be a culprit as otherwise I can't imagine what other code
>> could call RT internals and make it access the DB backend.
>
> Okay, there are two possible resolutions to this problem which spring
> to mind:
>
> * Arrange for database servers to start before Apache
>
> I'm not sure if this is feasible, but it seems to me that it's likely
> to be generally correct, given the layering implicit in database + web
> applications.
>
> * Arrange for RT to be more robust when a connection to the database fails
>
> This is certainly something worth exploring, but is likely to be a rather
> involved fix; not something I relish at this stage of the release cycle
> (diverging from upstream). Then again, perhaps changing Apache or MySQL
> (and the other database servers) would be more disruptive :)
>
> I've added the CC because I'm not sure where to start discussing
> whether the Apache/MySQL ordering can be changed. I had a look at
> Policy (which doesn't seem to mention dependency based booting at all;
> surely an inconsistency if it is to be enabled for squeeze?) and
> <http://wiki.debian.org/LSBInitScripts> which leads me to think that
> Apache needs something like "Should-Start: $database_server", but this
> is mainly guessing. I would appreciate input from those familiar with
> this part of the Debian infrastructure.

Perhaps for /etc/init.d/mysql-server (or whatever it is called)

# X-Start-Before:    apache2
# X-Stop-After:      apache2

I would think that it would be innocuous if apache2 was not installed.
Is there a way to reference the virtual package httpd in the LSB
headers?

-matt zagrabelny