linuxexpert-practice-labs/labs/ex294/7-5-desired-state/README.md

EX294 7.5: Desired state

Change a configuration file and restart the service only when the file changed, with handlers: by name, by a listen topic, and after a failure.

Before you start

This VM is the control node. The lab creates the user greg (password Lab-Pass-1) and installs ansible-core. Work as greg, in /home/greg/ansible: its ansible.cfg reads the inventory inventory, logs in to the nodes as devops with greg's SSH key, and becomes root.

The managed nodes node1 (10.99.1.11) and node2 (10.99.1.12) are AlmaLinux 10 containers in the group webservers, each with httpd installed and running with its stock /etc/httpd/conf/httpd.conf. For a root shell on a node, sudo podman exec -it node1 bash.

Tasks

1. Write /home/greg/ansible/web.yml, which sets ServerTokens Prod in /etc/httpd/conf/httpd.conf on the web servers and restarts httpd only when the file changed. The first run shows RUNNING HANDLER, the second doesn't and reports changed=0. Afterwards curl -sI http://node1/ shows Server: Apache without a version.
2. Write /home/greg/ansible/listen.yml, which sets KeepAlive On in the same file and notifies one listen topic that two handlers listen to. Both run, in the order they're defined.
3. Write /home/greg/ansible/force.yml, which sets Timeout 120 in the same file, notifies a handler that restarts httpd, and then runs a task that fails. Get the handler to run anyway. Without force_handlers the handler doesn't run; with it, it does.

Hints

• lineinfile with regexp and line, and notify: with the handler's exact name.
• Handlers take listen: TOPIC; the task notifies the topic.
• force_handlers: true on the play, or --force-handlers.
• To see a handler run again, take the line out first: ansible webservers -m lineinfile -a "path=... regexp=^Timeout state=absent".