Exercise 2: Installing firewalld Only on RedHat-Family Hosts — Possible Solution
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- name: Install firewalld on RedHat-family hosts
  yum:
    name: firewalld
    state: present
  when: ansible_os_family == "RedHat"

Explanation:

This directly mirrors the chapter's own ansible_os_family == "Debian"
example, just testing for "RedHat" instead and installing a package
appropriate to that family (firewalld, RedHat/CentOS/Fedora's own
common firewall management tool, using the yum module rather than
apt, since apt wouldn't exist on a RedHat-family host in the first
place). ansible_os_family is one of the automatically gathered facts
the chapter describes -- available without any extra setup, simply
because fact gathering ran at the start of the play. The when: clause
means this task is skipped entirely (not run, not reported as failed)
on any host where ansible_os_family isn't exactly "RedHat" -- so
running this same playbook against a mixed inventory of Debian and
RedHat-family hosts would only actually install firewalld on the
RedHat-family ones.

WHY THIS WORKS AS AN ANSWER
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This builds a correctly structured conditional task using the exact
when:/ansible_os_family pattern from the chapter's own example,
choosing an appropriately RedHat-specific module (yum) and package
(firewalld) rather than reusing Debian-specific tooling.