Support docker overlay storage driver

This is configured via docker_storage_driver.

ansible/roles/docker/defaults/main.yml

@@ -1,4 +1,8 @@
 ---
+# Name of the docker storage driver. Supported values include 'devicemapper'
+# and 'overlay'.
+docker_storage_driver: devicemapper
+
 # Name of the docker storage LVM volume group.
 docker_storage_volume_group:
 

ansible/roles/docker/tasks/main.yml

@@ -1,4 +1,11 @@
 ---
+- name: Fail when the storage driver is invalid
+  fail:
+    msg: >
+      Storage driver {{ docker_storage_driver }} is invalid. Valid drivers
+      include 'devicemapper' and 'overlay'.
+  when: docker_storage_driver not in ['devicemapper', 'overlay']
+
 - name: Ensure user is in the docker group
   user:
     name: "{{ ansible_user_id }}"
@@ -40,8 +47,8 @@
 - name: Fail when loopback-mode containers or images exist
   fail:
     msg: >
-      Not configuring docker storage in direct-lvm mode as loopback-backed
+      Not configuring docker storage in {{ docker_storage_driver }} mode as
-      containers or images exist.
+      loopback-backed containers or images exist.
   when:
     - "{{ 'Data loop file' in docker_info.stdout }}"
     - "{{ 'Images: 0' not in docker_info.stdout }}"

ansible/roles/docker/tasks/storage.yml

@@ -16,6 +16,7 @@
     - "/var/lib/docker/containers"
   become: True
 
+- block:
     - name: Ensure the docker storage data and metadata volumes exist
       lvol:
         vg: "{{ docker_storage_volume_group }}"
@@ -48,3 +49,4 @@
         lvchange --metadataprofile docker-thinpool
         {{ docker_storage_volume_group }}/{{ docker_storage_volume_thinpool }}
       become: True
+  when: docker_storage_driver == 'devicemapper'

ansible/roles/docker/templates/daemon.json.j2

@@ -1,11 +1,13 @@
 {
-  "storage-driver": "devicemapper",
+  "storage-driver": "{% if docker_storage_driver == 'devicemapper' %}devicemapper{% else %}overlay{% endif %}",
 {% if docker_daemon_mtu %}
   "mtu": {{ docker_daemon_mtu }},
 {% endif %}
   "storage-opts": [
+{% if docker_storage_driver == 'devicemapper' %}
     "dm.thinpooldev=/dev/mapper/{{ docker_storage_volume_group | replace('-', '--') }}-{{ docker_storage_volume_thinpool | replace('-', '--') }}",
     "dm.use_deferred_removal=true",
     "dm.use_deferred_deletion=true"
+{% endif %}
   ]
 }

etc/kayobe/docker.yml

@@ -2,6 +2,10 @@
 ###############################################################################
 # Docker configuration.
 
+# Name of the docker storage driver. Supported values include 'devicemapper'
+# and 'overlay'.
+#docker_storage_driver:
+
 # Name of the docker storage LVM volume group.
 #docker_storage_volume_group: