On wto, paź 20, 2009 at 01:26:24 -0700, jlist9 wrote:
> My understand is that nginx doesn't launch a process, being it a CGI process
> or FastCGI back-end server. I wonder what are the reasons behind this decision.
> I used to use another web server that takes care of launching FastCGI processes.
>
> The nice thing about it is that the web server checks if a backend process is
> running. If not, it automatically starts it. This means, for whatever reason if
> the backend process crashes, it will be re-launched. Also, the web server
> gets to control how many back-end server processes to start, according
> to the conf file. With this managing the processes is really easy, because
> it's all managed by the web server.
>
> This is a very handy feature. Any chance of having this in nginx?

We've been looking into it for quite some time but eventually decided
against it (we being mostly myself and I am definitely not speaking for
Nginx developers). Nginx supports some weird features like upgrading
binaries on the fly, which doesn't mesh with managing processes at all.
Or do you want to restart your application servers because you've just
made a "zero-downtime" upgrade of Nginx? Not so zero-downtime any more,
is it?

Like fellow posters said, spawning processes by the web server is not
a good idea (especially by a lean and mean server like Nginx). What
we're using (or at least migrating to) is supervisord[1] for process
management and a custom Nginx module for integration. We have Nginx
communicate with supervisord over XMLRPC to start/shutdown processes as
directed by the load balancer. Supervisord provides process management
way above Nginx could offer, while Nginx provides load data in real
time, so we have exactly as many backends as we need.

If you aim for simply running a pool of backends, look at supervisord,
period.

If you also want to size the pool dynamically, watch this space :)
ngx_supervisord isn't yet available (still waiting for finishing
touches) but consider this a pre-announcement. It's going to require
patches to the load balancer but if you're using upstream-fair, the
patch comes with the module source.

Best regards,
Grzegorz Nosek

1. http://www.supervisord.org/