Ansible: add items to single string conditionally - postgresql

Question

Currently working on ansible playbook for postgresql installation.
Trying to insert multiple values to shared_preload_libraries. Idea is to be able to insert them conditionnaly and different roles must be able to append to this line without overwriting it.
Current solution:
- name: Check whether postgresql.conf contains "pg_stat_statements"
command: grep "pg_stat_statements" "{{ pg_data }}/postgresql.conf"
register: check_shared_libs
check_mode: no
ignore_errors: yes
changed_when: no
- name: Modify postgresql.conf add pg_stat_statements shared library.
replace:
backup: yes
dest: "{{ pg_data }}/postgresql.conf"
regexp: "^#?(shared_preload_libraries = '.*)(')"
replace: '\1,pg_stat_statements\2'
when: check_shared_libs.rc != 0
notify: restart postgres
which gives me something like this: shared_preload_libraries = ',pg_stat_statements,powa,pg_stat_kcache,pg_qualstats,pg_wait_sampling'
Works fine, but I wonder if there's any better way to do it.

Answer 1

one way to avoid using the command task is the below. it comprises of 2 tasks because reading a remote file into a variable cant be done with a lookup plugin..
so, step1 we read the whole file into a variable and step2 we check if the variable contains the pg_stat_statements:
code:
---
- name: test play
hosts: localhost
connection: local
gather_facts: false
become: yes
vars:
pg_stat_statements_exists: false
tasks:
- name: read file
slurp:
src: /tmp/postgresql.conf
register: postgresql_file
- name: check pg_stat_statements exists
set_fact:
pg_stat_statements_exists: true
when: postgresql_file['content'] | b64decode is search('pg_stat_statements') == true
- name: print variable that will control the replace task that follows
debug:
var: pg_stat_statements_exists
and adding your replace task with the modified when condition:
- name: Modify postgresql.conf add pg_stat_statements shared library.
replace:
backup: yes
dest: "{{ pg_data }}/postgresql.conf"
regexp: "^#?(shared_preload_libraries = '.*)(')"
replace: '\1,pg_stat_statements\2'
when: pg_stat_statements_exists == true
notify: restart postgres
hope it helps