centos - Check if service exists with Ansible

Question

I have an Ansible playbook for deploying a Java app as an init.d daemon.

Being a beginner in both Ansible and Linux I'm having trouble to conditionally execute tasks on a host based on the host's status.

Namely I have some hosts having the service already present and running where I want to stop it before doing anything else. And then there might be new hosts, which don't have the service yet. So I can't simply use service: name={{service_name}} state=stopped, because this will fail on new hosts.

How I can I achieve this? Here's what I have so far:

  - name: Check if Service Exists
    shell: "if chkconfig --list | grep -q my_service;   then echo true;   else echo false; fi;"
    register: service_exists

# This should only execute on hosts where the service is present
  - name: Stop Service
    service: name={{service_name}} state=stopped
    when: service_exists
    register: service_stopped

# This too
  - name: Remove Old App Folder
    command: rm -rf {{app_target_folder}}
    when: service_exists

# This should be executed on all hosts, but only after the service has stopped, if it was present
  - name: Unpack App Archive
    unarchive: src=../target/{{app_tar_name}} dest=/opt

Answer 1

See the service_facts module, new in Ansible 2.5.

- name: Populate service facts
  service_facts:
- debug:
    msg: Docker installed!
  when: "'docker' in services"