Ansible/Roles

Playbook Roles

What are Ansible roles?

Roles allow you to split your playbook into different parts for different servers.

For example, a webapp with a database backend can define a webserver role and a database role, and it becomes much easier to modify the playbook to run these on the same host or on different hosts.

Feature: pre-tasks and post-tasks

In the playbook you can specify a pre-task and a post-task for a role.

For example, suppose you want to update aptitude before deploying the web server, and you want to send a notification to Slack when you are finished.

Then you could use the following playbook, which defines a pre_tasks list of things to do before the roles are defined, and a post_task list of things to do once the roles have been carried out.

- name: deploy mezzanine on vagrant
  hosts: web
  vars_files:
    - secrets.yml
  pre_tasks:
    - name: update the apt cache
      apt: update_cache=yes
  roles:
    - role: mezzanine
      database_host: "{{ hostvars.db.ansible_eth1.ipv4.address }}"
      live_hostname: 192.168.33.10.xip.io
      domains:
        - 192.168.33.10.xip.io
        - www.192.168.33.10.xip.io
  post_tasks:
    - name: notify Slack that the servers have been updated
      local_action: >
        slack
        domain=acme.slack.com
        token={{ slack_token }}
        msg="web server {{ inventory_hostname }} configured"

Feature: role files

If a role is particularly complicated or has details of its own to take care of, you can put all of the files specific to one particular role into a directory.

Suppose you have two roles, webserver and database. Then your directory structure would look like this:

playbooks/

        roles/
            database/
                tasks/
                    main.yml
                handlers/
                    main.yml
                files/
                    pg_hba.conf
                    postgresql.conf

            webserver/
                ...

The files folder contains two postgres configuration files:

• postgresql.conf configures postgres to accept connections on any network interface (since default is localhost only)
• pg_hba.conf configures postgres to accept a username and password to authenticate

Example

Let's look at an example of deploying an application with Ansible that a classic architecture: a web frontend with a database backend.

The web frontend can use an nginx web server playbook (see Ansible/Nginx Playbook for sample nginx playbook).