Make php-fpm default to serving on Unix sockets instead of TCP

[gregharvey]

This is actually more complicated than I realised, effectively we want ce-provision to default to using a Unix socket instead of TCP/IP (as it currently does) because we rarely actually have a PHP server cluster, usually PHP is on the same machine as the web server, so losing a load of performance to TCP/IP makes no sense in many cases. That being said, we still want to support TCP/IP, and this impacts NGINX and Apache configs, as they need to handle the config from the PHP-FPM role.

There's some incomplete WIP against the 1.x branch here, which can be used as inspiration but probably won't cleanly merge to 2.x any more:

• https://github.com/codeenigma/ce-provision/pull/860/files

[gregharvey]

The code from #860 is already in 2.x and ready to test.

[gregharvey]

The cachetool binary is now installed by ce-deploy and the adaptor is set using this role:

• https://github.com/codeenigma/ce-deploy/tree/1.x/roles/cache_clear/cache_clear-opcache

[gregharvey]

PR to fix cachetool in ce-deploy is here: codeenigma/ce-deploy#722

[gregharvey]

OK, fully tested NGINX with Unix sockets, that works well. Next is to try a code build and check on the ce-deploy side. There's a couple more PRs for some more cachetool tweaks over there:

• Php unix socket pr devel 1.x ce-deploy#725
• Php unix socket pr 1.x ce-deploy#724

Once that's tested we just need to make the same changes to the Apache role.

[gregharvey]

Fully tested all this on our own dev website and it worked fine. So next is Apache.