Why would I want to make a Jinja2 filter?

While Ansible Modules are the main way you accomplish something in Ansible, Jinja2 Filters are the main way you manipulate data.  The first python code you’ll need to write in ansible is probably because you want to transform some data to send to a module or template.

Where do I start?

First research how to accomplish the task in python.  In my case I might want to encrypt a string, so that it is encrypted on disk and my application can read it in and decrypt it in memory.  Then write the function that takes in at least one parameter, and returns one.

So here is my python code:

from base64 import b64encode
from base64 import b64decode
from Crypto.Cipher import AES
from Crypto import Random

pad = lambda s: s + (AES.block_size - len(s) % AES.block_size) * chr(AES.block_size - len(s) % AES.block_size)
unpad = lambda s: s[:-ord(s[len(s)-1:])]

def encrypt( inString, key ):
 inString = pad(inString)
 iv = Random.new().read( AES.block_size )
 cipher = AES.new( pad(key), AES.MODE_CBC, iv )
 return b64encode( iv + cipher.encrypt( inString ) )

Add in the Jinja2 glue code

Make sure you have the following at the top:

from __future__ import (absolute_import, division, print_function)
__metaclass__ = type

from jinja2 import Environment, FileSystemLoader
from ansible import errors

And add the mapping of jinja2 filter name to python function to the bottom:

class FilterModule(object):
 ''' adds encrypt filter ''' 
 def filters(self):
 return {

# filter map
 'encrypt': encrypt

Next save the plugin to a playbook to test it

From the developing plugins page, you can put this .py file in either /usr/share/ansible/plugins/filter_plugins/ or in a filter_plugins/ directory relative to your playbook.

Example Playbook:

Simply use the template module so you can use the custom filter in many ways:

- name: Render Testing Template
    src: test.j2
    dest: /tmp/test

Example Template:

{{ “Small string” | encrypt(“mypass”) }}
{{ “hello my name is simon, and I like to do drawlings” | encrypt(“mypass”) }}



Until Oscar gets an apartment,
Jonathan Malachowski

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