Jinja Templates with Ansible

Jinja templating can be used directly inside ansible playbooks, or you can use dedicated .j2 files with the ansible.builtin.template module.

They're great for dynamically formatting files/documents to display data in a consistent way.

Table of Contents

• Example: Daily System Health Check

Example: Daily System Health Check

Exampe provided by het_tanis and modified by me

A collection of tasks that will gather some basic health information about a system.
Then, the information is formatted into a jinja template and sent to a webhook.

---
# tasks file for daily_system_check

#Start with gathering all the variables from the systems

- name: Gather all the uptimes from all the systems
  ansible.builtin.shell: "uptime"
  register: uptime

#last --since "$(date -d 'now - 24hour' +'%Y-%m-%d %H:%M')"
- name: login information from the last 24 hours
  ansible.builtin.shell: 
    cmd: |
      last --since \"$(date -d 'now - 24hour' +'%Y-%m-%d %H:%M')\" | awk '{print $1}' | grep -vE 'root|wtmp' | sort | uniq -c |xargs| cut -c 2- 
  register: users_check


#Copy and save the templates for every run
- name: Push out a template for system check items
  ansible.builtin.template:
    src: templates/daily_health_check.j2
    dest: "/root/daily_health_check/daily_system_check.{{ ansible_date_time.iso8601_basic_short }}.txt"
  delegate_to: localhost
  run_once: yes

- name: Health report output capture
  ansible.builtin.shell: 
    cmd: |
      cat /root/daily_health_check/daily_system_check.{{ ansible_date_time.iso8601_basic_short }}.txt
  register: health_report
  delegate_to: localhost
  run_once: yes

- name: Send something simple to sandbox server using a wrapper module for ansible.builtin.uri
  ansible_discord_webhook:  # A custom module
    webhook_url: "{{discord_webhook_url}}"
    content: "{{health_report.stdout}}"
  when: discord_webhook_url is defined
  delegate_to: localhost
  run_once: yes

---

This is the template that the data will be formatted into, using the ansible.builtin.template module. This is the templates/daily_health_check.j2 template.

Total systems: {{ ansible_play_hosts_all | length }}
Unreachable systems:
----------------------------------------------
{% for host in ansible_play_hosts_all %}
{% if host not in ansible_play_hosts %}
{{ host }}
{% endif  %}
{% endfor %}

Reboot Report (Last 24 hours):
----------------------------------------------
{% for host in ansible_play_hosts_all %}
{% if hostvars[host].uptime is defined %}
{% if 'day' not in hostvars[host].uptime.stdout %}
{{ host }}
{% endif  %}
{% endif  %}
{% endfor %}

User Logins to Servers in last 24 hours:
----------------------------------------------
{% for host in ansible_play_hosts_all %}
{% if hostvars[host].users_check is defined %}
 {{ hostvars[host].ansible_hostname }} - {{ hostvars[host].users_check.stdout }}
{% endif %}
{% endfor %}

Processing a Template with lookup

By default, the template module writes out to a file. This may not always be what you want.

If you have a template to process but don't want to write it to a new file, you can use the lookup() filter.

This will process the template and expand all its variables, execute its if blocks, etc., and can be saved to a variable or used in another type of task.

- name: Process a template.
  ansible.builtin.set_fact:
    processed_template: "{{ lookup('template', 'template_name.j2') }}"

This will load the template file, populate it appropriately, and then save it to the processed_template variable (with set_fact).

---

A more practical example. We have a template that contains a single entry for a Samba share configuration.

# Template for the smb.conf entry itself, not the whole file
[{{ samba_share_name }}]
    path = {{ samba_dir }}
{% if browsable %}
    browsable = yes
{% else %}
    browsable = no
{% endif %}
{% if readonly %}
    read only = yes
{% else %}
    read only = no
{% endif %}
{% if guest_ok %}
    guest ok = yes
{% else %}
    guest ok = no
{% endif %}
{% if valid_users | length > 0 %}
    valid users = {{ valid_users | join(' ') }}
{% endif %}

Now, if we used ansible.builtin.template to render this into /etc/samba/smb.conf, it would replace the entire contents of the smb.conf file (and optionally make a backup), but that's not what needs to happen.

We want to append this expanded template to the smb.conf file.

We can use the ansible.builtin.blockinfile module in conjunction with the lookup() function.

- name: Append the output of the template to smb.conf
  ansible.builtin.blockinfile:
    path: /etc/samba/smb.conf
    marker: "# {mark} ANSIBLE MANAGED BLOCK - {{ samba_share_name }}"
    block: "{{ lookup('template', 'smb_conf_entry.j2') }}"

This will append the populated Jinja2 template to the smb.conf file (or update it, if it's already there) without overwriting the entire file.