How do I get the hosts from a specific section of an Ansible `hosts` file in a Jinja2 Template

Question

I have a hosts file including the following contents

[elasticsearch_nodes]
host1 os=linux
host2 os=linux
host3 os=linux

In a .j2 template I want to get the the list of [elasticsearch_nodes]

{{ some_ansible_magic_here }}

# should output "host1","host2","host3"

How do I do this?

I do have this as well to help with the quotes and the commas when I have the list.

{% for host in some_sort_of_ansible_magic_to_get_me_that_list_i_need %}
 "{{ host }}"{% if not loop.last %},{% endif %}
{% endfor %}

Answer 1

The magic you need is magic variables, in particular the groups variable, which is

a dictionary/map with all the groups in inventory and each group has the list of hosts that belong to it.

Then you can use template filters to format the list: use map with regex_replace to add the quotes to all list elements and then join them into the final result.

{{ groups['elasticsearch_nodes']|map('regex_replace', '(.*)', '"\\1"')|join(',') }}