Fix block_devices to not rely on device path

ansible/roles/block_devices/README.md

@@ -11,6 +11,8 @@ This is a convenience wrapper around the ansible modules:
 
 It includes logic to handle OpenStack-provided volumes appropriately both for appliance instances and the Packer build VM.
 
+To avoid issues with device names changing after e.g. reboots, devices are identified by serial number and mounted by filesystem UUID. 
+
 Requirements
 ------------
 
@@ -20,7 +22,7 @@ Role Variables
 --------------
 
 - `block_devices_partition_state`: Optional. Partition state, 'present' or 'absent' (as for parted) or 'skip'. Defaults to 'present'.
-- `block_devices_device`: Required. Path to block device, e.g. '/dev/sda'. See `community.general.parted:device` and `community.general.filesystem:dev`.
+- `block_devices_serial`: Required. Serial number of block device. For an OpenStack volume this is the volume ID.
 - `block_devices_number`: Required. Partition number, e.g 1 for "/dev/sda1". See `community.general.parted:number`.
 - `block_devices_fstype`: Required. Filesystem type, e.g.'ext4'. See `community.general.filesystem:fstype`
 - `block_devices_resizefs`: Optional. Grow filesystem into block device space, 'yes' or 'no' (default). See `community.general.filesystem:resizefs` for applicable fileysystem types.
@@ -51,7 +53,7 @@ Example Playbook
 The example variables below create an `ext4` partition on `/dev/sdb1` and mount it as `/mnt/files` with the default owner/group:
 
 ```yaml
-block_devices_device: /dev/sdb
+block_devices_serial: a1076455-da55-4e0c-bac8-ccc4698cff97
 block_devices_number: 1
 block_devices_fstype: ext4
 block_devices_path: /mnt/files
@@ -61,25 +63,12 @@ This does the same:
 
 ```yaml
 block_devices_configurations:
-  - device: /dev/sdb
+  - serial: a1076455-da55-4e0c-bac8-ccc4698cff97
     number: 1
     fstype: ext4
     path: /mnt/files
 ```
 
-This creates 'ext4' partitions on `/dev/sdb1` on `server` and `/dev/sdc1` on `server2`, both mounted at `/mnt/files`:
-
-```yaml
-block_devices_fstype: ext4
-block_devices_path: /mnt/files
-block_devices_number: 1
-block_devices_configurations:
-  - device: /dev/sdb
-    hostnames: server1
-  - device: /dev/sdc
-    hostnames: server2
-```
-
 License
 -------
 

ansible/roles/block_devices/library/block_devices.py

@@ -0,0 +1,44 @@
+#!/usr/bin/python
+
+# Copyright: (c) 2021, StackHPC
+# Apache 2 License
+
+DOCUMENTATION = r'''
+---
+module: block_devices
+
+short_description: Return block device paths by serial number.
+
+options: (none)
+
+author:
+    - Steve Brasier (@sjpb)
+'''
+
+RETURN = r'''
+devices:
+    description: dict with device serial numbers as keys and full paths (e.g. /dev/sdb) as values
+    type: dict
+    return: always
+'''
+
+import json
+
+from ansible.module_utils.basic import AnsibleModule
+
+def run_module():
+    module_args = dict()
+    module = AnsibleModule(argument_spec=module_args, supports_check_mode=True)
+    result = {"changed": False}
+    _, stdout, _ = module.run_command("lsblk --paths --json -O", check_rc=True)
+
+    device_info = json.loads(stdout)['blockdevices']
+    result['devices'] = dict((item['serial'], item['name']) for item in device_info)
+    module.exit_json(**result)
+
+def main():
+    run_module()
+
+
+if __name__ == '__main__':
+    main()

ansible/roles/block_devices/tasks/main.yml

@@ -1,33 +1,55 @@
+- name: Enumerate block device paths by serial number
+  block_devices:
+  register: _block_devices
+
 - name:  Create partitions
   parted:
-    device: "{{ item.get('device', block_devices_device) }}"
+    device: "{{ _device }}"
     number: "{{ item.get('number', block_devices_number) }}"
     state: "{{ item.get('partition_state', block_devices_partition_state) }}"
   when: "item.get('partition_state', block_devices_partition_state) != 'skip'"
   loop: "{{ block_devices_configurations }}"
+  vars:
+    _device: "{{ _block_devices.devices[ item.get('serial', block_devices_serial) ] }}"
 
 - name: Create filesystems
   filesystem:
     fstype: "{{ item.get('fstype', block_devices_fstype) }}"
-    dev: "{{ item.get('device', block_devices_device) }}{{ item.get('number', block_devices_number) }}"
+    dev: "{{ _device }}{{ item.get('number', block_devices_number) }}"
     resizefs: "{{ item.get('resizefs', block_devices_resizefs) }}"
     state: "{{ item.get('filesystem_state', block_devices_filesystem_state) }}"
   when: "item.get('filesystem_state', block_devices_filesystem_state) != 'skip'"
   loop: "{{ block_devices_configurations }}"
+  vars:
+    _device: "{{ _block_devices.devices[ item.get('serial', block_devices_serial) ] }}"
+
+- name: Get filesystem UUIDs
+  command:
+    cmd: "lsblk {{ _device }}{{ item.get('number', block_devices_number) }} --noheadings --output UUID"
+  loop: "{{ block_devices_configurations }}"
+  vars:
+    _device: "{{ _block_devices.devices[ item.get('serial', block_devices_serial) ] }}"
+  register: block_devices_uuids
+  changed_when: false
+  check_mode: no
 
 - name: Ensure mount point exists
   file:
     path: "{{ item.get('path', block_devices_path) }}"
     state: directory
   loop: "{{ block_devices_configurations }}"
 
-- name: Mount filesystems
+- name: Mount filesystems by UUID
   mount:
     path: "{{ item.get('path', block_devices_path) }}"
-    src: "{{ item.get('device', block_devices_device) }}{{ item.get('number', block_devices_number) }}"
+    src: "UUID={{ _uuid }}"
     fstype: "{{ item.get('fstype', block_devices_fstype) }}"
     state: "{{ item.get('mount_state', block_devices_mount_state) }}"
+  vars:
+    _uuid: "{{ block_devices_uuids.results[block_devices_idx].stdout }}"
   loop: "{{ block_devices_configurations }}"
+  loop_control:
+    index_var: block_devices_idx
 
 - name: Set owner/group for mounted directory
   file: