synchronous restart

Stephen Eley sfeley at
Tue Aug 31 16:29:56 EDT 2010

On Tue, Aug 31, 2010 at 4:08 PM, Jamie Wilkinson <jamie at> wrote:
> I should clarify... the above is exactly what I'm trying to avoid. i.e. how do you know if your new master failed to boot unless you are actively tailing the logs?

Well, first, you can specify a .pid file in your Unicorn configuration
file, then look at it before and a few seconds after the USR2 signal
to see if the process IDs are different.  Unicorn's pretty smart about
maintaining that file, and copying the old one out until you kill the
old process.

Second...  I'm confused as to why you think tailing the logs is
something to be avoided.  Isn't finding out status what logs are
*for?*  You could certainly automate the inspection and have some
process that emails you with an alarm if things don't look right.
Regardless of how you do it, if you're hoping to get away with
frequent automated deploys without *some* verification that requests
are working, you're taking big risks.  Even if your unicorn process
runs, you could still have problems at the application level throwing
exceptions at every user.

Have Fun,
   Steve Eley (sfeley at
   ESCAPE POD - The Science Fiction Podcast Magazine

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