Re: Struggling with logrotate and unicorn

From: Emmanuel Gomez <emmanuel.gomez@gmail.com>
To: Eric Wong <normalperson@yhbt.net>
Cc: unicorn list <mongrel-unicorn@rubyforge.org>
Subject: Re: Struggling with logrotate and unicorn
Date: Tue, 12 Apr 2011 11:36:38 -0700	[thread overview]
Message-ID: <91269EF1-4FEC-4CD3-82EE-4DF48F2544EE@gmail.com> (raw)
In-Reply-To: <20110412175855.GA21250@dcvr.yhbt.net>

On Apr 12, 2011, at 10:58 AM, Eric Wong wrote:
> Emmanuel Gomez <emmanuel.gomez@gmail.com> wrote:
>> I have confirmed that logrotate creates the logs with a 0600 umask and
>> the uid/gid of my unprivileged user (per my logrotate config, loosely
>> based on the example logrotate.conf from 3.4 or 3.5). 
> 
> Did the permissions of the old (rotated) log files change?

No, they remained owned by root.

>> The problem occurs when I send a USR1 signal to the master process (as
>> root, because the master is running as root) after the logs have been
>> rotated. As near as I can tell, after that the Unicorn master chowns
>> the logs to root ownership. Then, the workers attempt to chown the
>> logs back to ownership by the unprivileged user, which repeatedly
>> fails, spewing megabytes of errors that look like:
> 
> The rotation error handling should probably just exit! the worker
> and rely on the master to restart it...

That would probably be better behavior, although in this specific case the worker would immediately die on respawn because the log is still owned by root and unwriteable by my unprivileged user.

I did find a resolution: in the after_fork block, I had copied the code to switch users from the GitHub blog post on unicorn (https://github.com/blog/517-unicorn). I didn't see Unicorn::Worker#user, which implements the same code with the addition of a call to Unicorn::Util.chown_logs. When I replace the inline GitHub-blog-derived code with a call to Unicorn::Worker#user, it works. 

My understanding is that this (after_fork/Unicorn::Util.chown_logs) shouldn't be executed on USR1; I don't see how the Unicorn::Util.chown_logs call on after_fork (startup) would make a difference w/r/t rotation (much later), but my understanding is obviously incomplete, because it works.

Thanks for your reply, I'm off to comment on the GitHub blog post to try to warn others to use Unicorn::Worker#user instead of the example code in after_fork.

-- Emmanuel
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