added cache-clear service. update dispatcher queues

Signed-off-by: Jessica Mack <jmack@redhat.com>

awx/main/management/commands/run_cache_clear.py

@@ -0,0 +1,39 @@
+import logging
+
+from django.core.management.base import BaseCommand
+from django.conf import settings
+from django.core.cache import cache
+from awx.main.dispatch import pg_bus_conn
+from awx.conf import settings_registry
+
+logger = logging.getLogger('awx.main.cache_clear')
+
+
+class Command(BaseCommand):
+    """
+    Cache Clear
+    Runs as a management command and starts a daemon that listens for a pg_notify message to clear the cache.
+    """
+
+    help = 'Launch the cache clear daemon'
+
+    def handle(self, *arg, **options):
+        try:
+            with pg_bus_conn(new_connection=True) as conn:
+                conn.listen("tower_settings_change")
+                for e in conn.events(yield_timeouts=True):
+                    if e is not None:
+                        logger.info("Cache clear request received. Clearing now")
+                        # clear the cache of the keys in the payload
+                        setting_keys = e.payload
+                        orig_len = len(setting_keys)
+                        for i in range(orig_len):
+                            for dependent_key in settings_registry.get_dependent_settings(setting_keys[i]):
+                                setting_keys.append(dependent_key)
+                        cache_keys = set(setting_keys)
+                        logger.info('cache delete_many(%r)', cache_keys)
+                        cache.delete_many(cache_keys)
+        except Exception:
+            # Log unanticipated exception in addition to writing to stderr to get timestamps and other metadata
+            logger.exception('Encountered unhandled error in cache clear main loop')
+            raise