Re: Manual: why not restart service over killing the process

[Jason Conroy <conjaroy@gmail.com>]

Perhaps a third option is adding a Shepherd "reload" action for nginx to
perform the SIGHUP, similar to this?

https://git.savannah.gnu.org/cgit/guix.git/commit/gnu/services/base.scm?id=d3f75179e5741db29358e3e723146fd20ec79de9

I'm curious whether this approach has trade-offs compared to what's
documented in the manual.

Jason

On Sat, Nov 28, 2020 at 10:44 AM Christopher Baines <mail@cbaines.net>
wrote:

>
> EuAndreh <eu@euandre.org> writes:
>
> > Hi!
> >
> > The manual suggests a deploy-hook for the certbot-service-type that
> > looks like this:
> >
> > (define %nginx-deploy-hook
> >   (program-file
> >    "nginx-deploy-hook"
> >    #~(let ((pid (call-with-input-file "/var/run/nginx/pid" read)))
> >        (kill pid SIGHUP))))
> >
> > Instead of requiring the deploy-hook to know the path of the PID file,
> > why not restart the Shepherd service instead? Something like this:
> >
> > (define %nginx-deploy-hook
> >   (program-file
> >    "nginx-deploy-hook"
> >    (with-imported-modules '((gnu services herd))
> >      #~(begin
> >          (use-modules (gnu services herd))
> >          (restart-service 'nginx)))))
> >
> > If I understood correctly, those would result in equivalent outcomes,
> > and I tend to find the latter a more elegant approach. It is a bit
> > longer, but I like more restarting the service rather than killing the
> > process. Is there any downside I'm missing?
>
> You're sort of right, but you've got the downsides the wrong way around.
>
> The key bit with the kill call is the SIGHUP but, not that it's not
> SIGKILL. The current situation won't kill the NGinx process, but instead
> just get it to reload the certificate (at least that's the intention).
>
> The restart action would "kill" the process, in that it would send it
> SIGTERM and the the shepherd would start a new NGinx process, and this
> has the potential of interrupting whatever is using NGinx.
>
> Does that make sense?
>