Clean up caches periodically

Currently they're only cleaned up on demand, which can lead to
unnecessary disk usage on deployments that are not actively used.

Story: #2008909
Task: #42500
Change-Id: Id5b58d1d1b2bbd2988db7a08d4ccfe2166033147

ironic/conductor/manager.py

@@ -72,6 +72,7 @@ from ironic.conductor import utils
 from ironic.conductor import verify
 from ironic.conf import CONF
 from ironic.drivers import base as drivers_base
+from ironic.drivers.modules import image_cache
 from ironic import objects
 from ironic.objects import base as objects_base
 from ironic.objects import fields
@@ -100,6 +101,12 @@ class ConductorManager(base_manager.BaseConductorManager):
         super(ConductorManager, self).__init__(host, topic)
         self.power_state_sync_count = collections.defaultdict(int)
 
+    @METRICS.timer('ConductorManager._clean_up_caches')
+    @periodics.periodic(spacing=CONF.conductor.cache_clean_up_interval,
+                        enabled=CONF.conductor.cache_clean_up_interval > 0)
+    def _clean_up_caches(self, context):
+        image_cache.clean_up_all()
+
     @METRICS.timer('ConductorManager.create_node')
     # No need to add these since they are subclasses of InvalidParameterValue:
     #     InterfaceNotFoundInEntrypoint

ironic/conf/conductor.py

@@ -59,6 +59,10 @@ opts = [
                min=0,
                help=_('Interval between checks of orphaned allocations, '
                       'in seconds. Set to 0 to disable checks.')),
+    cfg.IntOpt('cache_clean_up_interval',
+               default=3600, min=0,
+               help=_('Interval between cleaning up image caches, in seconds. '
+                      'Set to 0 to disable periodic clean-up.')),
     cfg.IntOpt('deploy_callback_timeout',
                default=1800,
                min=0,

ironic/drivers/modules/image_cache.py

@@ -393,6 +393,13 @@ def clean_up_caches(ctx, directory, images_info):
     _clean_up_caches(directory, total_size)
 
 
+def clean_up_all():
+    """Clean up all entries from all caches."""
+    caches_to_clean = [x[1]() for x in _cache_cleanup_list]
+    for cache in caches_to_clean:
+        cache.clean_up()
+
+
 def cleanup(priority):
     """Decorator method for adding cleanup priority to a class."""
     def _add_property_to_class_func(cls):

releasenotes/notes/periodic-clean-up-29c33d2516bf16ec.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    All image caches are now cleaned up periodically, not only when used.
+    Set ``[conductor]cache_clean_up_interval`` to tune the interval or disable.