Fix restart HCAD detector bug (#460)

* Fix restart HCAD detector bug

To prevent repeatedly cold starting a model due to sparse data, HCAD has a cache that remembers we have done cold start for a model. A second attempt to cold start will need to wait for 60 detector intervals. Previously, when stopping a detector, I forgot to clean the cache. So the cache remembers the model and won’t retry cold start after some time. This PR fixes the bug by cleaning the cache when stopping a detector.

Testing done:
1. added unit and integration tests.
2. manually reproduced the issue and verified the fix.

Signed-off-by: Kaituo Li <kaituo@amazon.com>
(cherry picked from commit 9dd9718)

src/main/java/org/opensearch/ad/ml/EntityColdStarter.java

@@ -37,6 +37,7 @@
 import org.opensearch.action.ActionListener;
 import org.opensearch.action.support.ThreadedActionListener;
 import org.opensearch.ad.AnomalyDetectorPlugin;
+import org.opensearch.ad.CleanState;
 import org.opensearch.ad.MaintenanceState;
 import org.opensearch.ad.NodeStateManager;
 import org.opensearch.ad.caching.DoorKeeper;
@@ -63,7 +64,7 @@
  * Training models for HCAD detectors
  *
  */
-public class EntityColdStarter implements MaintenanceState {
+public class EntityColdStarter implements MaintenanceState, CleanState {
     private static final Logger logger = LogManager.getLogger(EntityColdStarter.class);
     private final Clock clock;
     private final ThreadPool threadPool;
@@ -743,4 +744,9 @@ public void maintenance() {
             }
         });
     }
+
+    @Override
+    public void clear(String detectorId) {
+        doorKeepers.remove(detectorId);
+    }
 }

src/main/java/org/opensearch/ad/transport/DeleteModelTransportAction.java

@@ -23,6 +23,7 @@
 import org.opensearch.ad.NodeStateManager;
 import org.opensearch.ad.caching.CacheProvider;
 import org.opensearch.ad.feature.FeatureManager;
+import org.opensearch.ad.ml.EntityColdStarter;
 import org.opensearch.ad.ml.ModelManager;
 import org.opensearch.ad.task.ADTaskCacheManager;
 import org.opensearch.cluster.service.ClusterService;
@@ -39,6 +40,7 @@ public class DeleteModelTransportAction extends
     private FeatureManager featureManager;
     private CacheProvider cache;
     private ADTaskCacheManager adTaskCacheManager;
+    private EntityColdStarter coldStarter;
 
     @Inject
     public DeleteModelTransportAction(
@@ -50,7 +52,8 @@ public DeleteModelTransportAction(
         ModelManager modelManager,
         FeatureManager featureManager,
         CacheProvider cache,
-        ADTaskCacheManager adTaskCacheManager
+        ADTaskCacheManager adTaskCacheManager,
+        EntityColdStarter coldStarter
     ) {
         super(
             DeleteModelAction.NAME,
@@ -68,6 +71,7 @@ public DeleteModelTransportAction(
         this.featureManager = featureManager;
         this.cache = cache;
         this.adTaskCacheManager = adTaskCacheManager;
+        this.coldStarter = coldStarter;
     }
 
     @Override
@@ -121,6 +125,8 @@ protected DeleteModelNodeResponse nodeOperation(DeleteModelNodeRequest request)
 
         cache.get().clear(adID);
 
+        coldStarter.clear(adID);
+
         // delete realtime task cache
         adTaskCacheManager.removeRealtimeTaskCache(adID);