Tasks, Modules, and Handlers

Part of the Ansible course

Picture a playbook that manages a web server. It has three tasks that each touch a different config file, and after any of them changes, the service needs a restart to pick up the new config. The obvious approach, restarting the service as its own task every time, is wasteful: if none of the three config tasks actually changed anything, you just restarted a perfectly fine service for no reason.

Ansible has a purpose-built answer for exactly this shape of problem: handlers. A handler is a task that only runs when something else tells it to, and even then, only once, no matter how many things told it to.