Ansible Simple Playbook Example with an FRR Template

This article describes a very simple Ansible example. Use it to learn Ansible; don’t use it as a production-level script. Please refer to the Demos and Training section for more robust examples with Ansible and other DevOp tools.

Ansible simple playbook

Playbook Requirements

The following is always required to run a playbook:

Optional files used in this example:

Install Ansible

The following was performed on Ubuntu:

cumulus@wbench:~$ sudo apt-get update
cumulus@wbench:~$ sudo apt-get install ansible

If you don’t have Ubuntu, you can install Ansible on Red Hat, Debian, CentOS, MacOS, any BSD distro, and so on. See this page on ansible.com.

Configure the Necessary Files

Simply cut and paste the code snippets from the code blocks below. Here are all the pieces of code used in the example.

Inventory File

The inventory is a single file called host with the contents "leaf1" inside.

cumulus@wbench:~$ cat host
leaf1

Again, this is a very simple example. Please read more about creating inventory files on ansible.com.

Playbook .yml File

cumulus@wbench:~$ cat sample-playbook.yml
---
- hosts: leaf1
  vars:
    description: “this is a leaf switch”
  remote_user: root
  tasks:
  - name: write the frr config file
    template: src=frr.j2 dest=/etc/frr/frr.conf
    notify:
    - restart frr
  - name: ensure frr is running
    service: name=frr state=started
  handlers:
    - name: restart frr
      service: name=frr state=restarted

This sample-playbook.yml contains one variable, two tasks, and a handler. Each component is described below:

ComponentDescription
hosts:leaf1Only run this playbook on the host leaf1.
varsThese are the variables defined for the playbook. There is only one variable, called description.
remote_userThis is the user who will run the playbook on the remote system.
tasksThere are two tasks listed, one uses the template module and one uses the service module.
handlersHandlers are tasks that only run if a task notifies it. A task will only notify it if something has changed. In this example, FRR gets restarted only if frr.conf changes.

jinja2 Template File

The template file can use any of the defined variables. The script below replaces the {{description}} with the one listed under vars:

cumulus@wbench:~$ cat frr.j2
!
interface lo
  description {{description}}
!

Run the Playbook

Use the ansible-playbook command to run the sample-playbook.yml file. Use the optional argument -i to point to the inventory file. If the -i option is not used, and there is no ansible.cfg folder indicating otherwise, Ansible will automatically use /etc/ansible/hosts. Alternately, instead of creating the file host with leaf1 in it, simply add leaf1 to /etc/ansible/hosts.

cumulus@wbench:~$ ansible-playbook sample-playbook.yml -i host

PLAY [leaf1] ******************************************************************

GATHERING FACTS ***************************************************************
ok: [leaf1]

TASK: [write the frr config file] ******************************************
changed: [leaf1]

TASK: [ensure frr is running] **********************************************
ok: [leaf1]

NOTIFIED: [restart frr] ****************************************************
changed: [leaf1]

PLAY RECAP ********************************************************************
leaf1                      : ok=4    changed=2    unreachable=0    failed=0

The playbook above runs both tasks. Since FRR was changed, it notifies the tasks, which restarts the FRR service. The playbook assumes that FRR was already running, otherwise this playbook will fail.