Capstone: Server Bootstrap Script

Part of the Bash course

A brand new server is a machine with nothing on it. Somebody has to install the web server, create the account you will log in with, put your SSH key in place, and schedule the checks that tell you it is still healthy. Doing that by hand takes twenty minutes and produces a machine nobody can reproduce, because the exact sequence lives only in your terminal history.

Think of a checklist for opening a shop. "Unlock the door" is not a safe instruction if the door might already be unlocked and the instruction is really "turn the key one notch", because doing it twice locks you out again. A safe checklist says "if the door is locked, unlock it." Idempotent describes exactly that: an operation you can perform any number of times and end up in the same state as performing it once. ...