playbooks/postgres/roles/attach/tasks/main.yaml

---
# Attach a service's network to Postgres.
#
# Postgres is the *base* unit and knows nothing about its clients, the same way
# Caddy knows nothing about its upstreams. A service that needs a database adds
# itself by dropping files next to postgres.container, and Quadlet merges them in.
#
# Include this from a service playbook:
#
#   - name: Attach this service to Postgres
#     ansible.builtin.include_tasks: "{{ playbook_dir }}/../postgres/roles/attach/tasks/main.yaml"
#     vars:
#       network_name: "{{ network_name }}"
#
# The including play must:
#
#   1. have created {{ network_name }}.network already — caddy/roles/register
#      does that, and every service here that needs a database is also behind
#      Caddy, so its register include comes first;
#   2. run the `podman` role (or include its task file and define the same four
#      vars), for podman_user and quadlet_dir;
#   3. define a "Restart Postgres" handler — see
#      roles/postgres/handlers/main.yaml for the exact snippet; and
#   4. flush handlers before starting the app, on a first attach. This include
#      notifies that restart, so by default it runs at the end of the play —
#      after the app has already started and failed to resolve `db`. A
#      `meta: flush_handlers` immediately after this include is enough; see
#      tandoor/roles/postgres for the working example.
#
# It runs as the connection user, which must be the rootless podman_user.
#
# A service may instead write these two files from its own role; the bytes have
# to match this file exactly, or the two will overwrite each other on every run.

- name: "Check that the {{ network_name }} network unit exists"
  ansible.builtin.stat:
    path: "{{ quadlet_dir }}/{{ network_name }}.network"
  register: postgres_attach_network

# A drop-in naming a .network file that does not exist makes Quadlet fail to
# generate the whole postgres unit, with a message that does not mention the
# drop-in at all. Fail here instead, where the cause is obvious.
- name: "Fail if {{ network_name }} has no network unit"
  ansible.builtin.assert:
    that: postgres_attach_network.stat.exists
    fail_msg: >-
      {{ quadlet_dir }}/{{ network_name }}.network does not exist, so attaching
      it to Postgres would break the postgres unit. Create the network first
      (caddy/roles/register does it), then include this file.

- name: Ensure the Postgres Quadlet drop-in directory exists
  ansible.builtin.file:
    path: "{{ quadlet_dir }}/{{ postgres_container | default('postgres') }}.container.d"
    state: directory
    owner: "{{ podman_user }}"
    group: "{{ podman_user }}"
    mode: '0755'

- name: "Attach {{ network_name }} to Postgres"
  ansible.builtin.copy:
    dest: >-
      {{ quadlet_dir }}/{{ postgres_container | default('postgres') }}.container.d/50-{{ network_name }}.conf
    owner: "{{ podman_user }}"
    group: "{{ podman_user }}"
    mode: '0644'
    content: |
      # Added by the {{ network_name }} playbook. Do not edit by hand.
      #
      # Deleting this file removes the network from {{ postgres_container | default('postgres') }} on
      # the next daemon-reload; nothing else changes.
      [Container]
      Network={{ network_name }}.network
  notify: Restart Postgres

# NetworkAlias= applies to every network the container joins, which is exactly
# right for a hub: every app in this repo reaches postgres as `db` (nextcloud,
# gitea, tandoor and outline use the alias; the rest use the container name).
# It is a fixed value in one shared file, not a per-service option, so the same
# bytes are written no matter how many services attach — two services writing
# their own aliases would make Quadlet pass --network-alias twice.
- name: "Give {{ postgres_container | default('postgres') }} the shared 'db' alias"
  ansible.builtin.copy:
    dest: >-
      {{ quadlet_dir }}/{{ postgres_container | default('postgres') }}.container.d/10-network-aliases.conf
    owner: "{{ podman_user }}"
    group: "{{ podman_user }}"
    mode: '0644'
    content: |
      # Shared container aliases for {{ postgres_container | default('postgres') }}.
      # Managed by Ansible (the service playbooks that use it). Do not edit.
      [Container]
      NetworkAlias=db
  notify: Restart Postgres