Exercise 1: A fail2ban Role's Directory Structure — Possible Solution
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roles/
  fail2ban/
    tasks/
      main.yml
    handlers/
      main.yml
    defaults/
      main.yml

Explanation:

This uses exactly the subset of the chapter's own standard role
layout that the exercise's own requirements call for -- tasks/main.yml
for the role's actual work (installing/configuring fail2ban),
handlers/main.yml for anything that needs to notify a restart (e.g.
restarting the fail2ban service after a config change, the same
notify/handler pattern from ansible1-6), and defaults/main.yml for
the "one default variable" the exercise specifies -- defaults is the
correct folder for this rather than vars, since the chapter names
defaults/main.yml as specifically meant to be overridable, which is
the natural fit for a single customizable setting like a ban duration
or a retry threshold. Folders the role doesn't currently need
(templates/, files/, meta/) are simply omitted rather than created
empty, since nothing in the exercise's own requirements calls for
them.

WHY THIS WORKS AS AN ANSWER
------------------------------
This sketches only the subdirectories the exercise's own stated needs
actually require, using the chapter's own folder names correctly, and
explicitly justifies choosing defaults/ over vars/ for the one
variable rather than picking one arbitrarily.