An awesome feature in that is not available in Ansible is immediate notification i.e. notifies :immediately. Ansible has notification handlers^[1] but they are only triggered at the end of the current playbook unlike Chef’s^[2] which can be triggered immediately! Moreover, you can configure Chef’s notifications to be triggered at specific times i.e. at the very end of a chef-client run i.e. :delayed or immediately i.e. :immediately.

Now, why I’m going into all these boring theories?? Well, when installing tomcat on Ubuntu, dpkg starts it automatically once the process is complete. I wanted to stop tomcat7 service, configure it, deploy its webapps & finally start it. So after installing tomcat7 I added a notification action to call a task that stops tomcat7 service.

tasks:
    - name: Install tomcat7
      apt: name={{ item }} install_recommends=no update_cache=yes state=present
      with_items:
        - tomcat7
        - tomcat7-admin
      notify:
        - Temporarily stop tomcat7

handlers:
    - name: Temporarily stop tomcat7
    service: name=tomcat7 state=stopped

Unfortunately, this didn’t work because notifications trigger tasks in handlers to run at the end of a playbook. So I had to come up with a quick fix for this issue.

Quick Fix

This involved registering a variable in task that installs tomcat packages i.e. register: tomcat_installed, then I would run the next task only if the registered variable has changed i.e. when: tomcat_installed|changed. Basically, handlers use a similar concept to this.

Here’s a snippet from the playbook showing my quick fix:

tasks:
    - name: Install tomcat7
      apt: name={{ item }} install_recommends=no update_cache=yes state=present
      with_items:
        - tomcat7
        - tomcat7-admin
      register: tomcat_installed

    - name: Temporarily stop tomcat7
      service: name=tomcat7 state=stopped
      when: tomcat_installed|changed

As you can see from the snippet, I’ve not used a handler. Yes that’s right, inorder to achieve the ‘effect’ of an immediate handler, I moved the task that stops tomcat7 service from the handler section to the tasks section.

As always, these are my opinions that I don’t mind sharing with anyone. Though I’m sure there are better solutions to my original problem, I think this solution could be useful for other ansible-related problems.

Further Reading

1. Ansible Handlers: Running Operations On Change
2. Chef Notifications