[Rt-devel] webmux connecting to the database; causing mod_perl startup to fail

[Dominic Hargreaves]

On Sat, Sep 11, 2010 at 11:38:32AM -0400, Jesse Vincent wrote:
> That's going to become impossible as we continue to move RT's configuration into the database. I consider having your database around before application startup to be a fairly serious requirement. Parallel startup scripts don't have a way to declare dependencies? How do you deal with, say, starting up apps that are mounted on NFS filesystems?

They do, but the problem is that I'm not in a position to mandate
the dependencies declared by Apache, and it's not just RT that fails
to start up but Apache in total, which may be used in other ways on the
same system.

There are network filesystem dependencies already included in the
parallel startup stuff, I believe. But as pointed out already, there
are some requirements you can't satisfy as easily: lack of a database
server on a remote host being the obvious one, so even if there was
sufficient information in the dependency information of the init
scripts, that doesn't solve the underlying problem.

I should have pointed out the short discussion on debian-devel on this
matter, which was fairly strongly of the opinion that RT shouldn't
break Apache in this way, and was also fairly negative about trying
to persuade the Apache maintainers to add some dependencies so Apache
will always start before the database servers:

http://lists.debian.org/debian-devel/2010/08/msg00786.html
and continuing:
http://lists.debian.org/debian-devel/2010/09/msg00011.html

If you think it's impossible to fix this in RT, then probably the
only thing we can do is deprecate support for mod_perl, and suggest
that people use FastCGI instead; because FastCGI doesn't turn fatal
errors in the application into a fatal error to start the web server
(certainly the Apache modules both seem to have a retry-with-backoff
approach to the problem). Or maybe there's a mod_perl trick to do a
similar thing which I'm not aware of.

Cheers,
Dominic.

-- 
Dominic Hargreaves, Systems Development and Support Team
Computing Services, University of Oxford
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