Ansible 101: Working With Facts and Templates

Published on
01-02-2024
Author
Aisys
Category
Interviews
https://cdn.aisys.pro/stories/ansible-101-working-with-facts-and-templates.jpg

In Ansible, variables and facts, along with templates, are foundational tools for creating flexible automation workflows. Variables allow you to manage and change your configurations dynamically. Facts are a special subset of variables that Ansible gathers from the remote systems, providing context-specific information.


Templates enable the generation of variable-driven configuration files, making your playbooks adaptable to varied environments and scenarios.


These tools make playbooks reusable and adaptable, allowing you to avoid hard-coding values and enabling customization for different environments.

Variables & Facts

Variables allow for parameters to be modified without altering the playbook's core logic.

How facts, variables, and templates work together

How facts, variables, and templates work together

  • Types of Variables:
    • Boolean: True or False values.

    • List: An ordered collection of items.

    • Dictionary: Key-value pairs for complex data structures.

    • Registered Variables: Captures the output of tasks to use later in your playbook.

    • Facts: Auto-collected variables that provide details about the remote systems you are managing.


NB: Avoid conflicts in variable names by using bracket notation.


- name: Print the distribution of the target
  hosts: all
  vars:
   curr_time: "{{ now() }}"
  tasks:
   - name: Distro Check
     ansible.builtin.debug:
      msg: "The target system is {{ ansible_facts['distribution'] }}. Timestamp: {{ curr_time }}"
      

Templates & Files

Templates in Ansible use the Jinja2 templating language to dynamically create files using variable interpolation, loops, and conditionals.


- name: Write distro name
  hosts: all
  tasks:
   - name: Write distro name
     ansible.builtin.template:
      src: distro.j2
      dest: /root/distro.txt
      mode: '644'

# src: location of jinja2 template file
# dest: location it will be copied to
# permissions that will be granted to the file

Practice

We're going to use the OS Family to determine whether to install NGINX of Lighttpd, and then, we'll deploy a custom homepage to the remote host containing NGINX all without hardcoding hostnames.


  1. Clone the repo.
git clone https://github.com/perplexedyawdie/ansible-learn.git


2. Change directory to facts-and-templates

cd ansible-learn/facts-and-templates


3. Spin up the environment using docker-compose

docker compose up -d --build


4. SSH into the Ansible server

ssh -o StrictHostKeyChecking=no -o NoHostAuthenticationForLocalhost=yes root@localhost -p 2200
# password: test123

Variables & Facts

5. Create a playbook called server_setup.yaml. Here, we'll setup NGINX & Lighttpd, and then, output the name of the distro for each remote host.


- name: Install NGINX on Debian & Lighttpd on RedHat
  hosts: all
  vars:
   dev1: "Debian"
   dev2: "RedHat"
  tasks:
   - name: Install NGINX for Debian-based systems   
     ansible.builtin.apt:
      name: nginx
      state: present
     when: ansible_facts['os_family'] == dev1       

   - name: Install Lighttpd for RedHat-based systems 
     ansible.builtin.yum:
      name: lighttpd
      state: present
     when: ansible_facts['os_family'] == dev2       

   - name: Display the distribution
     ansible.builtin.debug:
      msg: "The server is running {{ ansible_facts['distribution'] }}"


6. Run ansible-lint.

ansible-lint server_setup.yaml


7. Run the playbook.

ansible-playbook --key-file /root/.ssh/id_rsa_ansible -u root -i inventory.yaml server_setup.yaml


8. Confirm that the setup was successful.

ssh -i /root/.ssh/id_rsa_ansible root@server3 nginx -V

ssh -i /root/.ssh/id_rsa_ansible root@server2 lighttpd -v
ssh -i /root/.ssh/id_rsa_ansible root@server1 lighttpd -v

Templates & Files

9. Create a Jinja2 template file called index.html.j2


It will get auto-populated with the OS Family & Distribution.


<html>
<head>
  <title>Welcome to {{ ansible_facts['os_family'] }}</title>
</head>
<body>
  <h1>Server running on {{ ansible_facts['distribution'] }}</h1>
</body>
</html>


10. Create a playbook called custom_homepage.yaml.


We're deploying the custom homepage created above to NGINX then restarting the server.


- name: Deploy Custom Homepage and restart
  hosts: all
  vars:
   dev1: "Debian"
   dev2: "RedHat"
  tasks:
   - name: Create Homepage with Jinja2 Template for NGINX
     ansible.builtin.template:
      src: index.html.j2
      dest: /var/www/html/index.html
      mode: '644'
     when: ansible_facts['os_family'] == dev1
     notify: restart nginx

  handlers:
   - name: Restart NGINX
     listen: "restart nginx"
     ansible.builtin.service:
      name: nginx
      state: restarted
     when: ansible_facts['os_family'] == dev1


11. Run the linter.

ansible-lint custom_homepage.yaml


12. Run the playbook.


ansible-playbook --key-file /root/.ssh/id_rsa_ansible -u root -i inventory.yaml custom_homepage.yaml


13. Confirm deployment by visiting http://localhost:2203 in your browser.

Recap

Awesome effort! 🙌 We've learned how to use variables & facts in a playbook along with how to create dynamic files using templates. Next, we'll look at modularization and error handling. Til then, take care!


The DevOps Writing Contest is sponsored by Aptible. Aptible’s hosting platform automates the work of provisioning, managing, and scaling infrastructure, so developers can focus on what actually matters: their product. Get started for free with Aptible.

Discussion (20)

Not yet any reply