How to modularize Ansible playbook with multiple virtual hosts?

Question

^{(EDIT: the question was thoroughly rewritten based on feedback in comments, aiming to follow a suggestion to use "more code, less talk")}

I've accumulated some ansible playbooks for setting up our host(s). I want to start modularizing them. The current situation is roughly like below:

docker-registry-playbook.yml:

 - hosts: foo tasks: - name: install docker # ... - name: copy config files # ... - name: start docker registry # ...etc... 

issue-tracker-playbook.yml:

 - hosts: foo tasks: - name: install issue tracker # ...etc... 

tools-playbook.yml:

 - hosts: foo tasks: - name: configure nginx virtual hosts copy: src: "{{ item }}" dest: /etc/nginx/sites-available/ # ... with_items: - docker.example.com - issues.example.com - name: start nginx # ... - name: configure letsencrypt # ... 

My first idea was to split it into roles like below:

- hosts: foo
  roles: webserver docker_registry issue_tracker

However, in such case, I don't know how to make the webserver role "auto-detect" the host names (virtual hosts) it should expose? I would like to be easily able to move eg docker_registry role to a different host ( bar ), and have the webserver auto-detect the change and update virtual hosts accordingly when I change the new playbook to:

- hosts: foo
  roles: webserver docker_registry
- hosts: bar
  roles: webserver issue_tracker

I would strongly prefer not having to explicitly list virtual hosts as parameters to webserver both on foo and bar ; this would be too much duplication for me. Is it possible to have webserver autodetect names of "virtual hosts" from the other roles configured on the same server?

Or am I approaching the modularization in a wrong way, and the idiomatic approach in Ansible is to split it along some other axis when modularizing?

---

If not possible to do fully automatically, I'd like it to be done with minimal wiring; I could maybe grudgingly accept something like below, though it already looks much too long and ugly to me (but I still don't know how to do this in Ansible):

- hosts: foo
  roles:
  - docker_registry
  - role: webserver
    vars:
      vhosts: [ "docker_registry" ]

Answer 1

I'm not sure if I understand your problem correctly. Why is it necessary to have a common variable virtual_hosts in all roles?

... Initially, I thought I could set a variable in each of service1 and service2, named eg virtual_hosts: and Ansible would merge the duplicated variables into one...

For example:

- hosts: foo
  vars:
    virtual_host_service1: docker.example.com
    virtual_host_service2: issues.example.com
    webserver_vm:
      - "{{ virtual_host_service1 }}"
      - "{{ virtual_host_service2 }}"
  roles:
    - webserver
    - service1
    - service2

You might want to set the variables in the playbook, or in the host_vars, or in many other places according to the precedens