Exercise: Implementing handlers

Implementing handlers

• Define handlers in playbooks and notify them to apply configuration changes.

Prerequisites: Complete control-node setup and the preceding lessons in this chapter. Run commands as student on workstation unless a step names another machine.

From the project directory, run the relevant home-lab check. For an exercise with several checkpoints, grade each state before changing or removing it:

lab grade control-handlers

The grader reads project files and host state. A passing report covers the listed checks; also perform the task’s independent connection, repeat-run, and reboot checks where requested.

Change only the php-fpm configuration. Verify that nginx does not restart.

Record the published result first. The grader checks the original requirements, so a changed name or value may intentionally fail those checks.

Complete the supplied deployment so nginx and php-fpm restart only when their own configuration changes.

• Install the packages named by the project variables, then start and enable both services.
• Deploy the supplied nginx and php-fpm configurations to the destinations specified by the project.
• A change to one configuration must restart only its corresponding service. An unchanged repeat run must restart neither.
• Save the complete playbook and explain when the notified handlers execute.

The two .standard files are the stock Rocky Linux configuration files with one comment line added at the top. That extra line is what makes the copy tasks report changed on the first run.

Move into the project directory

[student@workstation ~]$ cd ~/control-handlers

Install the packages

Add a task that installs everything in packages. dnf accepts the whole list.

  tasks:
    - name: "{{ packages }} packages are installed"
      ansible.builtin.dnf:
        name: "{{ packages }}"
        state: present

Start and enable both services

    - name: Make sure the web service is running
      ansible.builtin.service:
        name: "{{ web_service }}"
        state: started
        enabled: true

    - name: Make sure the application service is running
      ansible.builtin.service:
        name: "{{ app_service }}"
        state: started
        enabled: true

Deploy each configuration file and notify its handler

Add two ansible.builtin.copy tasks: one installs the nginx configuration and notifies restart web service; the other installs the php-fpm configuration and notifies restart app service.

    - name: The {{ web_config_dst }} file has been deployed
      ansible.builtin.copy:
        src: "{{ web_config_src }}"
        dest: "{{ web_config_dst }}"
        force: true
      notify:
        - restart web service

    - name: The {{ app_config_dst }} file has been deployed
      ansible.builtin.copy:
        src: "{{ app_config_src }}"
        dest: "{{ app_config_dst }}"
        force: true
      notify:
        - restart app service

Define the two handlers

Add a handlers section, aligned with tasks, with a handler that restarts web_service and one that restarts app_service. Their names must match the notify entries exactly.

  handlers:
    - name: restart web service
      ansible.builtin.service:
        name: "{{ web_service }}"
        state: restarted

    - name: restart app service
      ansible.builtin.service:
        name: "{{ app_service }}"
        state: restarted

Check the syntax

[student@workstation control-handlers]$ ansible-navigator run \
> -m stdout configure_webapp.yml --syntax-check
playbook: /home/student/control-handlers/configure_webapp.yml

Run it: the handlers fire

[student@workstation control-handlers]$ ansible-navigator run \
> -m stdout configure_webapp.yml
...output omitted...
TASK [The /etc/nginx/nginx.conf file has been deployed] ************************
changed: [servera.lab.example.com]

TASK [The /etc/php-fpm.conf file has been deployed] ****************************
changed: [servera.lab.example.com]

RUNNING HANDLER [restart web service] ******************************************
changed: [servera.lab.example.com]

RUNNING HANDLER [restart app service] ******************************************
changed: [servera.lab.example.com]

PLAY RECAP *********************************************************************
servera.lab.example.com    : ok=8    changed=7    unreachable=0    failed=0  ...

The handlers appear as RUNNING HANDLER, after the last task.

Run it again: the handlers stay quiet

[student@workstation control-handlers]$ ansible-navigator run \
> -m stdout configure_webapp.yml
...output omitted...
PLAY RECAP *********************************************************************
servera.lab.example.com    : ok=6    changed=0    unreachable=0    failed=0  ...

The files already match, so the copy tasks report ok, nothing is notified, and neither service is restarted. If only nginx.conf changed in future, only restart web service would run.

Finish

Check your work with lab grade control-handlers, then put the exercise away with lab finish control-handlers.