Relaunch a php-fpm when Nginx finds a 502
Introduction
This shell script is to be used as a CGI with thttpd for automatically relaunching php-fpm whenever Nginx encounters a 502. This gives you piece of mind when you're developing a site and getting the hang of php-fpm is proving somewhat challenging.
Further elaboration
A simple README is hardly the place of describing such an involved process. Bear in mind that we're exploring more or less obscure Nginx directives and using thttpd in a rather strange way.
In a sense we're using
post_action to
implement a webhook that notifies
thttpd which in turn re-launches php-fpm.
The script also can launch php-fpm if it's not running. Hence it works in both cases:
-
php-fpm is stuck in a long, too long computation and it's better to put it out of it's misery and relaunch it so that we have our site back. Just catch the first 502 that shows up and fire up the relaunch.
-
php-fpm it's not running, hence we'll get a 502 at the outset.
This is in very broad strokes how the thing operates.
There are some security measures in place:
-
The script makes use of
superproviding a setuid root wrapper so that only the user that operates the php-fpm pool(s) in question can do the relauching. No root owned file or process was used on the making of this setup. -
It uses an internal redirect and an
internalNginx location. -
thttpd is bound to 127.0.0.1 (or ::1 if you prefer IPv6) and runs in an unprivileged port that should be blocked at the firewall level. In this case
8888.You can get the thttpd config on another github repo.
TODO
-
Make a blog post describing the all process and configuration and detail.
-
Make the script talk with RRDtool in order to have nice graphs showing the distribution of 502s on a time series.