When and why to use AF_UNIX, why work with the same machine

Question

I started studying the socket library in Python for the first time, and I realized that there is a constant called AF_UNIX that does the same thing as AF_INET but it is faster and establishes connection only with the same machine and uses the system file instead of internet connection

but what I didn't understand is why? why would i establish communication with my own machine? what use would that be and in what situation would it really be useful to use AF_UNIX?

Answer 1

Your question has many answers, I'll try to answer a few use cases for AF_UNIX:

1. You could use it to expose a private channel for other processes to communicate securely using files (since it'll respect the filesystem hierarchy and *nix permission model). PostgreSQL is known to expose a unix socket for it's psql cli to connect securely.

2. You could implement exchangeable communications using a socket protocol, as it's easy to move between AF_INET and AF_UNIX and expand it's communication throughout different hosts (redis and docker does this).

3. You could create a extendable and fast way for different processes and technologies to communicate without the device overhead AF_INET would include, even if you're using loopback interface.

The possibilities are actually limitless, as it includes a bit of personal preference. But the fact that AF_UNIX uses a similar specification as AF_INET makes it a powerful tool to extend communications between processes without having to rely on heavily different tools (FIFOs, shared mem, internal queues, files, to name a few).