Slides presented at the London Ansible Meetup in October 2018.

1. Jinja2 filters
Jiri Tyr

2. About me
● Using Ansible since 2014
● Ansible contributor
○ Modules: yum_repository , jenkins_plugin , ldap_attr, ldap_entry
○ Jinja2 filter: comment
○ Bug fixing (mount module)
○ Code reviews
● Author of more than 100 publicly available Ansible roles
○ https://github.com/jtyr
○ https://galaxy.ansible.com/jtyr

3. What is Jinja2 filter?

4. What is Jinja2 filter?
“Variables can be modified by filters. Filters are separated from the variable by a
pipe symbol (|) and may have optional arguments in parentheses. Multiple filters
can be chained. The output of one filter is applied to the next.”
source

5. What is Jinja2 filter?
data | filter

6. What is Jinja2 filter?
data | filter(value)

7. What is Jinja2 filter?
data | filter(param=value)

8. What is Jinja2 filter?
data | filter(param=value) | another_filter

9. What is Jinja2 filter?
● Filters built into Jinja2
○ http://jinja.pocoo.org/docs/2.10/templates/#list-of-builtin-filters
● Filters built into Ansible
○ https://docs.ansible.com/ansible/latest/user_guide/playbooks_filters.html

10. Where to use it in Ansible?

11. Where to use it in Ansible?
$ cat ./site.yaml
- name: My play
hosts: all
roles:
- role: app_role
where: >
ansible_os_family == 'RedHat' and
ansible_distribution_major_version | int >= 6

12. $ cat ./roles/app_role/defaults/main.yaml
app_config__default:
default:
server: example.com
port: 1234
app_config__custom: {}
app_config: "{{
app_config__default | combine(app_config__custom) }}"
$ cat ./roles/app_role/tasks/main.yaml
- name: My task
template:
src: app.cfg.j2
dest: "{{ app_config_file | default('/etc/app.cfg') }}"
mode: "{{ app_config_file_mode | default(omit) }}"
Where to use it in Ansible?

13. $ cat ./roles/app_role/templates/app.cfg.j2
{{ ansible_managed | comment }}
{{ app_config | encode_ini(ucase_prop=true) }}
Where to use it in Ansible?

14. How to write create Jinja2 filter?

15. How to write create Jinja2 filter?
def reverse(value):
# Reverse string or list of items
return value[::-1]
class FilterModule(object):
def filters(self):
return {
'reverse': reverse
}

16. How to distribute Jinja2 filter?

17. How to distribute Jinja2 filter?
● Contribute it to Ansible
○ See lib/ansible/plugins/filter for core filters
● Create *.py file in the filter_plugins directory on the role (playbook) level
○ Examples:
■ config_encoder_filters
■ docker_swarm

18. Thank you for your attention!
Questions?