Ansible jinja 2 template value should not changed - ansible

Question

I have written jinja2 template in ansible. What i am trying to achieve is that if the service_name is not mentioned and if service_name already exists on the remote machine, ansible should not change the service_name with default name mentioned in the template. However, when the service_name is not defined, ansible replaces service name with "abc" on remote machine even service_name exists. Any help would be appreciated.
active={{ active_status}}
instrument={{ instrument_status }}
{% if service_name is defined %}
service_name={{ service_name }}
{% else %}
service_name=abc
{% endif %}
Thanks

Answer 1

Following my above comment, here is a possible example implementation to meet your requirements. test_template.j2 is the exact copy of your current template. You can pass the service name as an extra variable to test (-e service_name=my_service)
Basically, if service_name is not defined, we:
Check if the remote file already exists and slurp its content into a var
Look for the relevant line in the file. Note: the regex_replace('None', '') is here to make sure we get an empty string if previous search/matches did not return anything.
Set the service name only if something relevant was found in the prior tasks
Once this check/setting is done correctly, you simply have to copy your template, what ever the case is.
---
- name: Conditional writing of template
hosts: localhost
gather_facts: false
vars:
my_dest: /tmp/test_file.txt
active_status: some active value
instrument_status: some instrument value
tasks:
- name: Try to read service name from existing file when it is not defined
when: service_name is not defined
block:
- name: Check if file exists
stat:
path: "{{ my_dest }}"
register: my_file
- name: Try to read target file if exists
slurp:
src: "{{ my_dest }}"
when: my_file.stat.exists
register: my_file_slurp
- name: Look for service name if there
set_fact:
looked_service: >-
{{
my_file_slurp.content
| b64decode
| regex_search('^service_name=.*$', multiline=true)
| regex_replace('^service_name=(.*)$', '\1')
| regex_replace('None', '')
}}
when: my_file.stat.exists
- name: Update service name if found
set_fact:
service_name: "{{ looked_service }}"
when: looked_service | default('') | length > 0
- name: Copy template file to destination
template:
src: test_template.j2
dest: "{{ my_dest }}"