The one_for_one policy means that if a child process terminates, it will get restarted. It is appropriate when the child processes managed by the supervisor are (relatively) independent. The contrasting policy is one_for_all where a terminating child will also induce a restart of all the other children of the supervisor. This is appropriate when there's a number of important dependencies between the children processes, and you'd better just rebuild the whole subtree.

It is key to run the thought process of system failure. You need to understand what will happen if a certain part of your system errors out in an unforeseen way and make sure your restart policies are likely to right the ship.

The should be a first comma after “crashes” IMHO.

“It” is the child.

So if the supervisor (“parent”) has other children, they won’t be restarted