What are the differences from running PHP-FPM over an Unix Socket vs a TCP/IP Socket?

Question

There are these two ways of running PHP-FPM. I know that nothing is bullet-proof in tech, but what are the pros and cons from both methods?

Solution

The difference is mainly the added overhead of using the full network stack to "pack" and "unpack" every piece of data. Mind you that the overhead is negligible for most deployments

• Using a socket (e.g. listen = '/tmp/php-fpm.sock') makes sense when both the front-end (e.g. Nginx) and php-fpm are in the same box and

  1. You have the option to scale horizontally both the front and back-end together (say you are building a container with both and you can create more containers, each with a working pair) or
  2. Your only option is to scale vertically the one "box" you are using (say, you add more CPU, RAM, etc)

• Using a TCP connection (e.g. listen = 127.0.0.1:9000) makes sense if you want to de-couple the front and the back-end, for example, if you decide to scale up your environment by having a single Nginx receiving connections and passing the work via the network to a cluster of php-fpm boxes

Every environment is different, so as always, the only true option is to start with the one setup that seems right, load-test, and keep measuring the performance so you can try different options as your load requirements evolve (normally, you go with the one that is cheaper to implement or easier to maintain, since both are solid, battle-tested approaches)