Set nova config for rbd instance folder cleanup after evacuations

After evacuations and revert resizes when using rbd storage backend,
the instance folder is usually left behind and causes issues when
migrating the instance back to the host.
With the config option set, the nova-compute service will cleanup
those folders as part of the periodic checks that run for instances
that have been evacuated/migrated.

Closes-bug: #2019141
Change-Id: I846ccb0a95d04139b41fdad6cbf465d303d6cc09

hooks/nova_compute_context.py

@@ -17,6 +17,7 @@ import os
 import platform
 import shutil
 import socket
+import subprocess
 import uuid
 
 from typing import (
@@ -97,6 +98,16 @@ def _network_manager():
     return manager()
 
 
+def is_local_fs(path):
+    result = False
+    try:
+        subprocess.check_call(["df", "-l", path])
+        result = True
+    except subprocess.CalledProcessError as e:
+        log("Error invoking df -l {}: {}".format(path, e), level=DEBUG)
+    return result
+
+
 def get_availability_zone():
     use_juju_az = config('customize-failure-domain')
     juju_az = os.environ.get('JUJU_AVAILABILITY_ZONE')
@@ -324,6 +335,17 @@ class NovaComputeLibvirtContext(context.OSContextGenerator):
 
         if config('libvirt-image-backend'):
             ctxt['libvirt_images_type'] = config('libvirt-image-backend')
+            if config('libvirt-image-backend') == 'rbd':
+                instances_path = config('instances-path')
+                if instances_path in ('', None):
+                    instances_path = '/var/lib/nova/instances'
+                if is_local_fs(instances_path):
+                    ctxt['ensure_libvirt_rbd_instance_dir_cleanup'] = True
+                else:
+                    log("Skipped enabling "
+                        "'ensure_libvirt_rbd_instance_dir_cleanup' because"
+                        " instances-path is not a local mount.",
+                        level=INFO)
 
         ctxt['force_raw_images'] = config('force-raw-images')
         ctxt['inject_password'] = config('inject-password')

templates/train/nova.conf

@@ -370,6 +370,9 @@ lock_path=/var/lock/nova
 
 [workarounds]
 disable_libvirt_livesnapshot = False
+{% if ensure_libvirt_rbd_instance_dir_cleanup -%}
+ensure_libvirt_rbd_instance_dir_cleanup = {{ ensure_libvirt_rbd_instance_dir_cleanup }}
+{% endif -%}
 
 {% include "parts/section-ephemeral" %}
 

templates/yoga/nova.conf

@@ -353,6 +353,9 @@ lock_path=/var/lock/nova
 
 [workarounds]
 disable_libvirt_livesnapshot = False
+{% if ensure_libvirt_rbd_instance_dir_cleanup -%}
+ensure_libvirt_rbd_instance_dir_cleanup = {{ ensure_libvirt_rbd_instance_dir_cleanup }}
+{% endif -%}
 
 {% include "parts/section-ephemeral" %}
 

unit_tests/test_nova_compute_contexts.py

@@ -386,6 +386,36 @@ class NovaComputeContextTests(CharmTestCase):
              'reserved_host_disk': 0,
              'reserved_host_memory': 512}, libvirt())
 
+    @patch.object(context.subprocess, 'check_call')
+    def test_ensure_rbd_cleanup_rbd(self, call_mock):
+        self.lsb_release.return_value = {'DISTRIB_CODENAME': 'focal'}
+        self.os_release.return_value = 'ussuri'
+        self.test_config.set('libvirt-image-backend', 'rbd')
+        libvirt = context.NovaComputeLibvirtContext()
+        result = libvirt()
+        self.assertIn('ensure_libvirt_rbd_instance_dir_cleanup', result)
+        self.assertTrue(result['ensure_libvirt_rbd_instance_dir_cleanup'])
+        call_mock.assert_called_once_with(
+            ['df', '-l', '/var/lib/nova/instances'])
+
+    @patch.object(context.subprocess, 'check_call')
+    def test_ensure_rbd_cleanup_rbd_non_local_mount(self, call_mock):
+        self.lsb_release.return_value = {'DISTRIB_CODENAME': 'focal'}
+        self.os_release.return_value = 'ussuri'
+        call_mock.side_effect = [context.subprocess.CalledProcessError(
+            1, 'df -l /var/foo/bar')]
+        self.test_config.set('libvirt-image-backend', 'rbd')
+        self.test_config.set('instances-path', '/var/foo/bar')
+        libvirt = context.NovaComputeLibvirtContext()
+        self.assertNotIn('ensure_libvirt_rbd_instance_dir_cleanup', libvirt())
+        call_mock.assert_called_once_with(['df', '-l', '/var/foo/bar'])
+
+    def test_ensure_rbd_cleanup_non_rbd(self):
+        self.lsb_release.return_value = {'DISTRIB_CODENAME': 'focal'}
+        self.os_release.return_value = 'ussuri'
+        libvirt = context.NovaComputeLibvirtContext()
+        self.assertNotIn('ensure_libvirt_rbd_instance_dir_cleanup', libvirt())
+
     def test_libvirt_context_inject_password(self):
         self.lsb_release.return_value = {'DISTRIB_CODENAME': 'zesty'}
         self.os_release.return_value = 'ocata'