"unicorn -D" always returns 0 "success" (even when failed to load)

Eric Wong normalperson at yhbt.net
Wed Dec 23 02:26:17 EST 2009


Iñaki Baz Castillo <ibc at aliax.net> wrote:
> Hi, I'm writing a Debian init script for unicorn and realized that when 
> starting unicorn with daemonize option, the command always returns 0, even if 
> the start action failed (due for example Errno::EADDRINUSE).
> 
> Returning 0 in such case is not good as it breaks service init scripts or 
> service controllers (as HeartBeat) that fully rely on the appropriate exit 
> code.
> 
> Is there some way to determine if unicorn failed to start when using "-D"?

Hi Iñaki,

No way to determine that currently, as I've never encountered the need.

For validating startups, most folks I know have specific endpoint(s) in
application dedicated to checks.  That way they can get way more info
and all the way down into stack including things like database/memcached
connections.

Anything less is superficial because they can fail to detect other
misconfigurations (including stuff like wrong RAILS_ENV); not just
startup errors.

> Another related issue: When the Rack config.ru file contains some error (as a 
> typo) the worker(s) returns 1 (at the moment usually). Then unicorn master 
> process reapes the terminated worker process and restarts it. Of course it 
> would fail again and again. Anyhow "unicorn -D" returns 0 again (success).
> 
> Usually if a worker (all the workers) fail to start at the moment of running 
> it, it obviously means that there is some error in the application with 
> prevents it to run. It could be great if Unicorn could detect it.

I'm generally hesitant to introduce code/features/bloat that aren't
helpful to people who properly test configurations before deploying :)

Adding this code doesn't solve problems.  Either way the site can become
inaccessible/unusable and problems are noticeable very quickly.

If there's sufficient interest, I'll consider accepting a small patch
for this.  Right now I'm unconvinced...

> For that I suggest something as a new option "--validation-time TIME". Let's 
> suppose TIME is 5 seconds. In case *all* the workers fail within 5 seconds 
> after starting unicorn, then unicorn understands that the Rack application is 
> wrong (or any other error as Errno::EADDRINUSE) so terminates all the workers 
> and itself (and hopefully returns 1 or any other non-zero exit status).
> 
> Of course, all the above means that Unicorn should wait TIME seconds before 
> being daemonized (so after TIME seconds it can decide which code to return).
> 
> Does it make sense? Thanks a lot.

We avoid introducing command-line options since they're unlikely to be
compatible with "rackup" parsing of the "#\" lines in .ru files.

-- 
Eric Wong


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