Remove `/etc/docker/daemon.json` when no Docker options are set anymore

group_vars/matrix_servers

@@ -21,6 +21,8 @@ matrix_playbook_docker_installation_enabled: true
 
 matrix_playbook_docker_installation_daemon_options: "{{ matrix_playbook_docker_installation_daemon_options_auto | combine(matrix_playbook_docker_installation_daemon_options_custom, recursive=True) }}"
 
+matrix_playbook_docker_installation_daemon_options_file_path: /etc/docker/daemon.json
+
 # Since Docker 27.0.1, Docker daemon options do not need to be changed to enable IPv6 support on the daemon side.
 # See: https://docs.docker.com/engine/release-notes/27/#ipv6
 # We only enable `ip6tables` and `experimental` for people who explicitly request it (perhaps due to running an old Docker version).

roles/custom/matrix_playbook_migration/tasks/docker_daemon_options_file_cleanup.yml

@@ -0,0 +1,20 @@
+---
+
+# ansible-role-docker creates the Docker daemon options file (`/etc/docker/daemon.json`) when options are set
+# via `matrix_playbook_docker_installation_daemon_options` (which influences the `docker_daemon_options` variable of the role).
+# See: https://github.com/geerlingguy/ansible-role-docker/blob/acade8d01f11bcd5efecba6d8211138d7567ce4b/tasks/main.yml#L53-L66
+#
+# However, it doesn't delete the file when the options list is empty.
+#
+# This means that people who previously force-disabled IPv6 (and injected `{'ipv6': false}` options, etc)
+# or had some other custom options had that file created for them.
+# Later, when they stopped setting these options, they were stuck with the configuration file that still retained them.
+#
+# Here, we make the file go away of no options are set.
+# Idealy, this task would be part of the `ansible-role-docker` role, but it's not (yet).
+- name: Ensure the Docker daemon options file is deleted when no longer needed
+  when: matrix_playbook_docker_installation_daemon_options.keys() | length == 0
+  ansible.builtin.file:
+    path: "{{ matrix_playbook_docker_installation_daemon_options_file_path }}"
+    state: absent
+  notify: restart docker

roles/custom/matrix_playbook_migration/tasks/main.yml

@@ -28,6 +28,15 @@
   block:
     - ansible.builtin.include_tasks: "{{ role_path }}/tasks/debian_docker_trusted_gpg_d_migration_migration.yml"
 
+- when: matrix_playbook_docker_installation_enabled | bool
+  tags:
+    - setup-all
+    - install-all
+    - setup-docker
+    - install-docker
+  block:
+    - ansible.builtin.include_tasks: "{{ role_path }}/tasks/docker_daemon_options_file_cleanup.yml"
+
 - tags:
     - setup-all
     - install-all