How to exclude an host in Ansible Jinja2 template for-loop? - for-loop

Question

I have a template named foo.yml.j2 used in an Ansible task to generate a foo.yml file:
{% for host in ansible_play_hosts_all %}
{{ host }},
{% endfor %}
Everything works fine except I need something like the following statement: For every host in ansible_play_hosts_all except for host==bar do this or that.
Is this achievable or the only way to do this is to categorize my hosts in different groups and use ansible_play_hosts_group?

Answer 1

You can use the reject filter to take your host out of the list so that it is not part of your loop:
{% for host in ansible_play_hosts_all | reject('==', 'bar') %}
{{ host }},
{% endfor %}

Answer 2

There are more options. The trivial one is using the condition in Jinja
{% for host in ansible_play_hosts_all %}
{% if host != 'bar' %}
{{ host }},
{% endif %}
{% endfor %}
Fit the format to your needs.
Example of a complete playbook for testing
- hosts: host_1,host_2,host_3
gather_facts: false
tasks:
- debug:
msg: |
{% for host in ansible_play_hosts_all %}
{% if host != 'host_2' %}
{{ host }},
{% endif %}
{% endfor %}
run_once: true
gives (abridged)
msg: |-
host_1,
host_3,
The next option is to remove blacklisted hosts from the loop, e.g.
blacklist: [host_2]
The template below gives the same result
{% for host in ansible_play_hosts_all|difference(blacklist) %}
{{ host }},
{% endfor %}