/ansible_templating_demo

Introduction to Ansible Templating with Jinja2 for Ansible-Indianapolis meetup on 9/19/2017

Ansible Templating Demo

This project introduces Ansible Templating to new or intermediate experience levels. It was prepared for the Ansible-Indianapolis meetup.

Prerequisites

  1. Ansible, git and python must be installed on the Control machine.

    Mac

    1. Install homebrew and use it to install the required packages.
    ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"  
brew install git python ansible

    Linux

    1. Install required system packages.
    yum install epel-release libffi-devel python-devel openssl-devel gcc sshpass  
# For Debian systems, use:  
# apt install libffi-dev python-dev libssl-dev gcc sshpass
    1. Install pip and git.
    yum install python-pip git ansible
# For Debian systems, replace yum with apt

  2. Create virtual environment to work in.

    pip install virtualenv  
# virtualenv will make a folder for you  
virtualenv ~/path/to/project  
cd ~/path/to/project

  3. Clone the ansible_templating_demo repo into the project folder.

    git clone https://github.com/clearobject/ansible_templating_demo.git

You should be ready to go! (did somebody just clone the readme from another repo???)

Ansible Templating (Jinja2)

Ansible uses Jinja2 templating to enable dynamic expressions and access to variables. Jinja2 is a modern and designer-friendly templating language for Python, modelled after Django’s templates. It is fast, widely used and secure with the optional sandboxed template execution environment.

From Jinja2 Template Designer Documentation:

A Jinja template is simply a text file. Jinja can generate any text-based format (HTML, XML, CSV, LaTeX, etc.). A Jinja template doesn’t need to have a specific extension: .html, .xml, or any other extension is just fine.

A template contains variables and/or expressions, which get replaced with values when a template is rendered; and tags, which control the logic of the template. The template syntax is heavily inspired by Django and Python.

Filters

Filters are used for transforming data inside a template expression. Jinja2 ships with many filters. See builtin filters in the official Jinja2 template documentation for a full listing. In addition the ones provided by Jinja2, Ansible ships with it’s own and allows users to add their own custom filters. See Ansible Filters for this listing.

Note: Templating happens on the Ansible controller, not on the task’s target host, so filters also execute on the controller as they manipulate local data.

Tests

Tests in Jinja2 are a way of evaluating template expressions and returning True or False. Jinja2 ships with many of these. See builtin tests in the official Jinja2 template documentation. Tests are very similar to filters and are used mostly the same way, but they can also be used in list processing filters, like C(map()) and C(select()) to choose items in the list. In addition to those Jinja2 tests, Ansible supplies a few more and users can easily create their own.

Note: Like all templating, tests always execute on the Ansible controller, not on the target of a task, as they test local data.

Examples

basic string manipulation

Example What it does Times incountered in our automation
{{ variable_name | upper() }} converts text value of variable to upper case 20
{{ variable_name | lower() }} converts text value of variable to lower case 13
{{ variable_name | capitalize() }} adds capitalization for text value of variable 4
{{ variable_name | uri_split(0) }} pulls data out of a URI formatted value 2
{{ variable_name | urlencode }} applies url encoding to value 1
{{ variable_name | password_hash('sha512') }} hashes a password value 1
{{ variable_name | to_json }} or {{ variable_name | to_nice_json }} renders value as JSON 3

basic number manipulation

Example What it does Times incountered in our automation
{{ variable_name | round }} round to nearest whole number 4
{{ variable_name | min }} get the minimum value from list of numbers 2

variable control

Example What it does Times incountered in our automation
{{ variable_name | default(true) }} provides a default value inline for variable 44
{{ variable_name | mandatory }} require variable inline 1
{{ variable_name | int }} explicit type conversion to integer 4