Nginx – Unicorn master failed to start error

Indeed, a limitation of upstart is that it cannot track daemons that do what unicorn is doing.. that being fork/exec and exit their main process. Believe it or not, sshd does the same thing on SIGHUP, and if you look, /etc/init/ssh.conf makes sure sshd runs in the foreground. This is also one reason apache2 still uses an init.d script.

It sounds like gunicorn actually sort of daemonizes itself when receiving SIGUSR1 by forking and then exitting. This would be confusing for any of the process managers out there that try and keep a process alive.

I think you have two options. 1 is just to not use the SIGUSR1 and stop/start gunicorn when you need it.

The other option is to not use upstart's pid tracking, and just do this:

start on ..
stop on ..

pre-start exec gunicorn -D --pid-file=/run/gunicorn.pid
post-stop exec kill `cat /run/gunicorn.pid`

Not as sexy as pid tracking, but at least you won't have to write a whole init.d script.

(incidentally, this has nothing to do with the shebangs/execs. Both of those things work just like running a regular executable, so they wouldn't cause any extra forks).

No, there is no option to restart individual virtual server instances. However, there shouldn't even be any need to do that when app server is upgraded.