Add docker installation as role

roles/install-docker/handlers/main.yml

@@ -0,0 +1,6 @@
+---
+- name: restart docker
+  service:
+    name: docker
+    state: restarted
+    enabled: yes

roles/install-docker/tasks/main.yml

@@ -0,0 +1,85 @@
+# This file is a mash-up of:
+#   https://github.com/geerlingguy/ansible-role-docker/blob/master/tasks/docker-compose.yml
+#   https://www.digitalocean.com/community/tutorials/how-to-install-docker-compose-on-debian-9
+#   and our own stuff …
+---
+- name: Gather package facts
+  package_facts:
+    manager: "auto"
+
+- name: Exit if docker.io is installed
+  fail:
+    msg: "Please remove docker.io (Debian vanilla docker package) first!"
+  when: "'docker.io' in ansible_facts.packages"
+
+- name: Install Docker APT deps
+  package:
+    name: "{{ packages }}"
+    state: present
+  vars:
+    packages:
+    - apt-transport-https
+    - ca-certificates
+    - gnupg2
+    - software-properties-common
+
+- name: add Docker apt-key
+  apt_key:
+    url: https://download.docker.com/linux/debian/gpg
+    state: present
+
+- name: add Docker's APT repository
+  apt_repository:
+   repo: deb https://download.docker.com/linux/debian buster stable
+   state: present
+   update_cache: true
+   filename: 'docker'
+
+- name: install Docker
+  package:
+    name: "{{ packages }}"
+    state: present
+  vars:
+    packages:
+    - docker-ce
+    - python-docker
+
+- name: Set docker configuration
+  copy:
+    dest: /etc/docker/daemon.json
+    content: |
+      {
+          "exec-opts": ["native.cgroupdriver=systemd"],
+          "log-driver": "json-file",
+              "log-opts": {
+                  "max-size": "100m"
+              }
+      }
+  notify: restart docker
+
+- name: Check current docker-compose version.
+  command: docker-compose --version
+  register: docker_compose_current_version
+  changed_when: false
+  failed_when: false
+
+- name: Delete existing docker-compose version if it's different.
+  file:
+    path: "{{ docker_compose_path }}"
+    state: absent
+  when: >
+    docker_compose_current_version.stdout is defined
+    and docker_compose_version not in docker_compose_current_version.stdout
+
+- name: Install Docker Compose (if configured).
+  get_url:
+    url: https://github.com/docker/compose/releases/download/{{ docker_compose_version }}/docker-compose-Linux-x86_64
+    dest: "{{ docker_compose_path }}"
+    mode: 0755
+
+- name: Place admin users in docker group
+  user:
+    name: "{{ item }}"
+    groups: docker
+    append: yes
+  with_items: "{{ docker_users }}"