Looping through a list when building group_vars in ansible - loops

Question

I'm rather new to ansible and would like to deploy prometheus-grok-exporter (via ansible-grok-exporter role) with a specific configuration for all my nodes that run the cacti application.
My inventory is like this:
cacti_first ansible_host=192.168.50.50
cacti_second ansible_host=192.168.50.51
[group__cacti]
cacti_first
cacti_second
Inside group_vars/group__cacti I want to add something like this:
---
prometheus_grok_services_template:
- name: cacti_metrics
config_version: 3
input:
type: file
paths:
{% for cacti_dir in cacti_path %}
- "{{cacti_dir}}/log/cacti.log"
{% endfor %}
readall: false
extaConfigContinuesFromHere: true
And I have host config like this:
host_vars/cacti_first:
---
cacti_path:
- /usr/share/cacti
prometheus_grok_services:
- prometheus_grok_services_template
host_vars/cacti_second:
---
cacti_path:
- /usr/share/cacti
- /usr/share/cacti2
prometheus_grok_services:
- prometheus_grok_services_template
Inside the playbook I do a loop for prometheus_grok_services and use the yaml data to provision the service.
Now - this works as long as I don't try to use a loop inside group_vars/group__cacti. ansible-inventory reports that:
$ ansible-inventory -i hosts --list cacti_second
ERROR! Syntax Error while loading YAML.
found character that cannot start any token
The error appears to be in '/home/bastion/ansible-playbooks/group_vars/group__cacti': line 8, column 10, but may
be elsewhere in the file depending on the exact syntax problem.
The offending line appears to be:
paths:
{% for cacti_dir in cacti_path %}
^ here
So, I'd like to ask - is it allowed to do jinja loops to build yaml for group vars? Is it a syntax error on my end? How am I supposed to template it?
I'd like to avoid moving the block to host vars (which I know works), mostly because it's a large piece of code (about 2KB of yaml config) and it's not as elegant as using group vars.
Thanks!

Answer 1

Fix the group_vars. For example
shell> cat group_vars/group__cacti
---
prometheus_grok_services_template:
- name: cacti_metrics
config_version: 3
input:
type: file
paths: "{{ paths_str|from_yaml }}"
readall: false
extaConfigContinuesFromHere: true
paths_str: |
{% for cacti_dir in cacti_path %}
- {{ cacti_dir }}/log/cacti.log
{% endfor %}
Then, the playbook
- hosts: group__cacti
gather_facts: false
tasks:
- debug:
msg: "{{ lookup('vars', item) }}"
loop: "{{ prometheus_grok_services }}"
gives
ok: [cacti_first] => (item=prometheus_grok_services_template) =>
msg:
- config_version: 3
input:
extaConfigContinuesFromHere: true
paths:
- /usr/share/cacti/log/cacti.log
readall: false
type: file
name: cacti_metrics
ok: [cacti_second] => (item=prometheus_grok_services_template) =>
msg:
- config_version: 3
input:
extaConfigContinuesFromHere: true
paths:
- /usr/share/cacti/log/cacti.log
- /usr/share/cacti2/log/cacti.log
readall: false
type: file
name: cacti_metrics

Answer 2

You can't use this kind of for loop in a variables file or a playbook - it only works in template files. To acheive what you're after, you can use product filters, as described https://docs.ansible.com/ansible/latest/user_guide/playbooks_filters.html#products
In your example, you would have:
---
prometheus_grok_services_template:
- name: cacti_metrics
config_version: 3
input:
type: file
paths: "{{ cacti_path | product(['/log/cacti.log']) | map('join') | list }}"
readall: false
extaConfigContinuesFromHere: true