Switch default docker storage driver to overlay2

To avoid switching existing deployments from devicemapper to overlay2,
we check the existing storage driver configuration directly with the
Docker daemon, or if unreachable by reading the /etc/docker/daemon.json
configuration file.

Co-Authored-By: Pierre Riteau <pierre@stackhpc.com>
Story: 2005667
Task: 30972

Change-Id: Iaf2ee8c9f302f4684ae039bb00b2e2e5969cf1fc

ansible/docker-devicemapper.yml

@@ -1,11 +1,44 @@
 ---
-- name: Ensure docker devicemapper storage is configured
+- name: Verify and configure Docker storage driver
   hosts: docker
   tags:
     - docker
     - docker-devicemapper
   tasks:
-    - name: Ensure docker devicemapper storage is configured
+    - name: Check for existing Docker configuration using devicemapper
+      block:
+      - name: Query Docker daemon for storage driver
+        docker_host_info:
+        failed_when: false
+        register: docker
+
+      - block:
+        - name: Check for a Docker configuration file
+          become: True
+          stat:
+            path: /etc/docker/daemon.json
+          register: docker_config_file
+
+        - name: Check whether devicemapper is used in configuration file
+          lineinfile:
+            path: /etc/docker/daemon.json
+            regexp: 'storage-driver.*devicemapper'
+            state: absent
+          become: True
+          changed_when: False
+          # `check_mode: True` ensures that we don't modify daemon.json
+          check_mode: True
+          register: devicemapper_docker
+          when: docker_config_file.stat.exists
+        when: not docker.can_talk_to_docker
+
+      - name: Fail if devicemapper is in use while another storage driver was requested
+        fail:
+          msg: "Docker storage driver {{ docker_storage_driver }} was requested, but devicemapper is in use"
+        when: (docker.can_talk_to_docker and docker.host_info.Driver == 'devicemapper') or (devicemapper_docker.found | default(0) == 1)
+      when: docker_storage_driver != 'devicemapper'
+
+    - name: Ensure Docker devicemapper storage is configured
       include_role:
         name: docker-devicemapper
       when: docker_storage_driver == 'devicemapper'

ansible/group_vars/all/docker

@@ -2,8 +2,8 @@
 ###############################################################################
 # Docker configuration.
 
-# Name of the docker storage driver. Default is 'devicemapper'.
-docker_storage_driver: devicemapper
+# Name of the docker storage driver. Default is 'overlay2'.
+docker_storage_driver: overlay2
 
 # Name of the docker storage LVM volume group.
 docker_storage_volume_group: data

ansible/roles/docker-devicemapper/defaults/main.yml

@@ -1,6 +1,6 @@
 ---
 # Name of the docker storage driver.
-docker_storage_driver: devicemapper
+docker_storage_driver: overlay2
 
 # Name of the docker storage LVM volume group.
 docker_storage_volume_group:

ansible/roles/kolla-ansible/defaults/main.yml

@@ -262,7 +262,7 @@ kolla_enable_host_ntp:
 # Docker configuration.
 
 # Name of the docker storage driver.
-docker_storage_driver: devicemapper
+docker_storage_driver: overlay2
 
 # Name of the docker storage LVM volume group.
 docker_storage_volume_group:

doc/source/configuration/reference/hosts.rst

@@ -690,8 +690,8 @@ Docker engine configuration is applied by both Kayobe and Kolla Ansible (during
 bootstrap-servers).
 
 The ``docker_storage_driver`` variable sets the Docker storage driver, and by
-default the ``devicemapper`` driver is used. If using this driver, see
-:ref:`configuration-hosts-lvm` for information about configuring LVM for
+default the ``overlay2`` driver is used. If using the ``devicemapper`` driver,
+see :ref:`configuration-hosts-lvm` for information about configuring LVM for
 Docker.
 
 Various options are defined in ``${KAYOBE_CONFIG_PATH}/docker.yml``

etc/kayobe/docker.yml

@@ -2,7 +2,7 @@
 ###############################################################################
 # Docker configuration.
 
-# Name of the docker storage driver. Default is 'devicemapper'.
+# Name of the docker storage driver. Default is 'overlay2'.
 #docker_storage_driver:
 
 # Name of the docker storage LVM volume group.

releasenotes/notes/default-overlay2-970bdb5b7b62b60a.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - |
+    The default Docker storage driver has been changed from ``devicemapper`` to
+    ``overlay2``, which is the storage driver preferred by Docker. Environments
+    using ``devicemapper`` should set ``docker_storage_driver`` to
+    ``devicemapper`` in ``${KAYOBE_CONFIG_PATH}/docker.yml``.