Ansible Simple Playbook Example with an FRR Template
This article describes a very simple Ansible example. Use it to learn Ansible; do not use it as a production-level script. Refer to the Demos and Training section for more robust examples with Ansible and other DevOps tools.
Playbook Requirements
The following is always required to run a playbook:
Optional files used in this example:
Install Ansible
Run the following commands on Ubuntu:
cumulus@wbench:~$ sudo apt-get update
cumulus@wbench:~$ sudo apt-get install ansible
If you do not 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
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. Read more about creating inventory files.
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. The following table describes each component:
| Component | Description |
|---|---|
| hosts:leaf1 | Only run this playbook on the host leaf1. |
| vars | These are the variables defined for the playbook. There is only one variable, called description. |
| remote_user | This is the user who runs the playbook on the remote system. |
| tasks | A list of two tasks, one using the template module and one using the service module. |
| handlers | Handlers are tasks that only run if a task notifies it. A task only notifies 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 automatically uses /etc/ansible/hosts. Alternately, instead of creating the file host with leaf1 in it, just 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. Because it changed FRR, it notifies the tasks, which restarts the FRR service. The playbook assumes that FRR was already running, otherwise this playbook is going to fail.