8 - Templating with Jinja2
Objective
This exercise will cover Jinja2 templating. Ansible uses Jinja2 templating to modify files before they are distributed to managed hosts. Jinja2 is one of the most used template engines for Python, take a look at the documentation for additional information.
Guide
Step 1 - Using Templates in Playbooks
When a template for a file has been created, it can be deployed to the managed hosts using the template module, which supports the transfer of a local file from the control node to the managed hosts.
As an example of using templates you will change the motd file to contain host-specific data.
First create the directory templates to hold template resources in ~/ansible-files/:
Then in the ~/ansible-files/templates/ directory create the template file motd-facts.j2:
Welcome to {{ ansible_hostname }}.
{{ ansible_distribution }} {{ ansible_distribution_version}}
deployed on {{ ansible_architecture }} architecture.
The template file contains the basic text that will later be copied over. It also contains variables which will be replaced on the target machines individually.
Next we need a playbook to use this template. In the ~/ansible-files/ directory create the Playbook motd-facts.yml:
---
- name: Fill motd file with host data
hosts: node1
become: true
tasks:
- name: Deploy message of the day file
ansible.builtin.template:
src: motd-facts.j2
dest: /etc/motd
owner: root
group: root
mode: "0644"
As we just learned what handlers do, let's add one to this playbook. Add the handlers block with a simple task, which just outputs a message:
---
- name: Fill motd file with host data
hosts: node1
become: true
handlers:
- name: Motd_changed
ansible.builtin.debug:
msg: "The Message of the Day was updated! SSH to node1 and check the content."
tasks:
- name: Deploy message of the day file
ansible.builtin.template:
src: motd-facts.j2
dest: /etc/motd
owner: root
group: root
mode: "0644"
Before we do a bigger challenge lab, let's see if you remember how handlers are triggered. Currently, the handler is not triggered, add the missing keyword to the task, which deploys the template.
Solution
Add the notify keyword and the name of the handler:
---
- name: Fill motd file with host data
hosts: node1
become: true
handlers:
- name: Motd_changed
ansible.builtin.debug:
msg: "The Message of the Day was updated! SSH to node1 and check the content."
tasks:
- name: Deploy message of the day file
ansible.builtin.template:
src: motd-facts.j2
dest: /etc/motd
owner: root
group: root
mode: "0644"
notify: Motd_changed
You have done this a couple of times by now:
- Understand what the Playbook does.
- Execute the Playbook
motd-facts.yml. - Observe if the handler was triggered. Re-Run the playbook multiple times.
- Login to node1 via SSH and check the message of the day content.
- Log out of node1.
You should see how Ansible replaces the variables with the facts it discovered from the system. The handler was only triggered when the task reported a changed state.
Step 2 - Challenge Lab
Add a line to the template to list the current kernel of the managed node.
- Find a fact that contains the kernel version using the commands you learned in the "Ansible Facts" chapter.
Tip
Filter for kernel.
Run the newly created playbook to find the fact name.
-
Change the template to use the fact you found.
-
Run the motd playbook again.
-
Check motd by logging in to node1
Solution
Find the fact:
---
- name: Capture Kernel Version
hosts: node1
tasks:
- name: Collect only kernel facts
ansible.builtin.setup:
filter:
- '*kernel'
register: setup_output
- name: Output variable content
ansible.builtin.debug:
msg: "{{ setup_output }}"
With the wildcard in place, the output shows:
TASK [debug] *******************************************************************
ok: [node1] => {
"setup": {
"ansible_facts": {
"ansible_kernel": "4.18.0-305.12.1.el8_4.x86_64"
},
"changed": false,
"failed": false
}
}
With this we can conclude the variable we are looking for is labeled ansible_kernel.
Then we can update the motd-facts.j2 template to include ansible_kernel as part of its message.
Modify the template motd-facts.j2:
Welcome to {{ ansible_hostname }}!
Host runs {{ ansible_distribution }} {{ ansible_distribution_version}}
Deployed on {{ ansible_architecture }} architecture
The kernel version is {{ ansible_kernel }}
Run the playbook.
Verify the new message via SSH login to node1.