Retaining context in APEX Engine based on policies received in PdpUpdate

Change-Id: I73fad5bf76ed6b4979f5ab76013f204ea82da30b
Issue-ID: POLICY-2215
Signed-off-by: a.sreekumar <ajith.sreekumar@est.tech>

7 files changed, 210 insertions, 79 deletions

diff --git a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexActivator.java b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexActivator.java
index 2c3fac151..6c86c1eff 100644
--- a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexActivator.java
+++ b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexActivator.java
@@ -21,11 +21,13 @@
 
 package org.onap.policy.apex.service.engine.main;
 
+import java.io.IOException;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.stream.Stream;
 import lombok.Getter;
+import lombok.Setter;
 import org.onap.policy.apex.model.basicmodel.concepts.ApexException;
 import org.onap.policy.apex.model.basicmodel.handling.ApexModelException;
 import org.onap.policy.apex.model.basicmodel.service.ModelService;
@@ -59,8 +61,12 @@ public class ApexActivator {
 
     // The parameters of the Apex activator when running with multiple policies
     @Getter
+    @Setter
     private Map<ToscaPolicyIdentifier, ApexParameters> apexParametersMap;
 
+    @Getter
+    Map<ToscaPolicyIdentifier, AxPolicyModel> policyModelsMap;
+
     // Event unmarshalers are used to receive events asynchronously into Apex
     private final Map<String, ApexEventUnmarshaller> unmarshallerMap = new LinkedHashMap<>();
 
@@ -99,46 +105,7 @@ public class ApexActivator {
                 .mapToInt(p -> p.getEngineServiceParameters().getInstanceCount()).sum();
             apexParameters.getEngineServiceParameters().setInstanceCount(totalInstanceCount);
             instantiateEngine(apexParameters);
-            Map<ToscaPolicyIdentifier, AxPolicyModel> policyModelsMap = new LinkedHashMap<>();
-            Map<String, EventHandlerParameters> inputParametersMap = new LinkedHashMap<>();
-            Map<String, EventHandlerParameters> outputParametersMap = new LinkedHashMap<>();
-
-            for (Entry<ToscaPolicyIdentifier, ApexParameters> apexParamsEntry : apexParametersMap.entrySet()) {
-                ApexParameters apexParams = apexParamsEntry.getValue();
-                boolean duplicateInputParameterExist =
-                    apexParams.getEventInputParameters().keySet().stream().anyMatch(inputParametersMap::containsKey);
-                boolean duplicateOutputParameterExist =
-                    apexParams.getEventOutputParameters().keySet().stream().anyMatch(outputParametersMap::containsKey);
-                if (duplicateInputParameterExist || duplicateOutputParameterExist) {
-                    LOGGER.error("I/O Parameters for " + apexParamsEntry.getKey().getName() + ":"
-                        + apexParamsEntry.getKey().getVersion()
-                        + " has duplicates. So this policy is not executed");
-                    apexParametersMap.remove(apexParamsEntry.getKey());
-                    continue;
-                } else {
-                    inputParametersMap.putAll(apexParams.getEventInputParameters());
-                    outputParametersMap.putAll(apexParams.getEventOutputParameters());
-                }
-                // Check if a policy model file has been specified
-                if (apexParams.getEngineServiceParameters().getPolicyModelFileName() != null) {
-                    LOGGER.debug("deploying policy model in \""
-                        + apexParams.getEngineServiceParameters().getPolicyModelFileName()
-                        + "\" to the apex engines . . .");
-
-                    final String policyModelString = TextFileUtils
-                        .getTextFileAsString(apexParams.getEngineServiceParameters().getPolicyModelFileName());
-                    AxPolicyModel policyModel = EngineServiceImpl
-                        .createModel(apexParams.getEngineServiceParameters().getEngineKey(), policyModelString);
-                    policyModelsMap.put(apexParamsEntry.getKey(), policyModel);
-                }
-            }
-            AxPolicyModel finalPolicyModel = aggregatePolicyModels(policyModelsMap);
-            // Set the policy model in the engine
-            apexEngineService.updateModel(apexParameters.getEngineServiceParameters().getEngineKey(),
-                finalPolicyModel, true);
-            setUpMarshallerAndUnmarshaller(apexParameters.getEngineServiceParameters(), inputParametersMap,
-                outputParametersMap);
-            setUpmarshalerPairings(inputParametersMap);
+            setUpModelMarhsallerAndUnmarshaller(apexParameters);
         } catch (final Exception e) {
             LOGGER.debug(APEX_ENGINE_FAILED_MSG, e);
             throw new ApexActivatorException(APEX_ENGINE_FAILED_MSG, e);
@@ -147,8 +114,50 @@ public class ApexActivator {
         LOGGER.debug("Apex engine started as a service");
     }
 
+    private void setUpModelMarhsallerAndUnmarshaller(ApexParameters apexParameters) throws IOException, ApexException {
+        policyModelsMap = new LinkedHashMap<>();
+        Map<String, EventHandlerParameters> inputParametersMap = new LinkedHashMap<>();
+        Map<String, EventHandlerParameters> outputParametersMap = new LinkedHashMap<>();
+
+        for (Entry<ToscaPolicyIdentifier, ApexParameters> apexParamsEntry : apexParametersMap.entrySet()) {
+            ApexParameters apexParams = apexParamsEntry.getValue();
+            boolean duplicateInputParameterExist =
+                apexParams.getEventInputParameters().keySet().stream().anyMatch(inputParametersMap::containsKey);
+            boolean duplicateOutputParameterExist =
+                apexParams.getEventOutputParameters().keySet().stream().anyMatch(outputParametersMap::containsKey);
+            if (duplicateInputParameterExist || duplicateOutputParameterExist) {
+                LOGGER.error("I/O Parameters for {}:{} has duplicates. So this policy is not executed.",
+                    apexParamsEntry.getKey().getName(), apexParamsEntry.getKey().getVersion());
+                apexParametersMap.remove(apexParamsEntry.getKey());
+                continue;
+            }
+            inputParametersMap.putAll(apexParams.getEventInputParameters());
+            outputParametersMap.putAll(apexParams.getEventOutputParameters());
+            // Check if a policy model file has been specified
+            if (apexParams.getEngineServiceParameters().getPolicyModelFileName() != null) {
+                LOGGER.debug("deploying policy model in \"{}\" to the apex engines . . .",
+                    apexParams.getEngineServiceParameters().getPolicyModelFileName());
+
+                final String policyModelString =
+                    TextFileUtils.getTextFileAsString(apexParams.getEngineServiceParameters().getPolicyModelFileName());
+                AxPolicyModel policyModel = EngineServiceImpl
+                    .createModel(apexParams.getEngineServiceParameters().getEngineKey(), policyModelString);
+                policyModelsMap.put(apexParamsEntry.getKey(), policyModel);
+            }
+        }
+        AxPolicyModel finalPolicyModel = aggregatePolicyModels(policyModelsMap);
+        // Set the policy model in the engine
+        apexEngineService.updateModel(apexParameters.getEngineServiceParameters().getEngineKey(), finalPolicyModel,
+            true);
+        setUpMarshallerAndUnmarshaller(apexParameters.getEngineServiceParameters(), inputParametersMap,
+            outputParametersMap);
+        setUpMarshalerPairings(inputParametersMap);
+    }
+
     private AxPolicyModel aggregatePolicyModels(Map<ToscaPolicyIdentifier, AxPolicyModel> policyModelsMap) {
         Map.Entry<ToscaPolicyIdentifier, AxPolicyModel> firstEntry = policyModelsMap.entrySet().iterator().next();
+        ToscaPolicyIdentifier tempId = new ToscaPolicyIdentifier(firstEntry.getKey());
+        AxPolicyModel tempModel = new AxPolicyModel(firstEntry.getValue());
         Stream<Entry<ToscaPolicyIdentifier, AxPolicyModel>> policyModelStream =
             policyModelsMap.entrySet().stream().skip(1);
         Entry<ToscaPolicyIdentifier, AxPolicyModel> finalPolicyModelEntry =
@@ -157,13 +166,16 @@ public class ApexActivator {
                     entry1.setValue(
                         PolicyModelMerger.getMergedPolicyModel(entry1.getValue(), entry2.getValue(), true, true));
                 } catch (ApexModelException exc) {
-                    LOGGER.error("Policy model for " + entry2.getKey().getName() + ":" + entry2.getKey().getVersion()
-                        + " is having duplicates. So this policy is not executed", exc.getMessage());
+                    LOGGER.error("Policy model for {} : {} is having duplicates. So this policy is not executed.",
+                        entry2.getKey().getName(), entry2.getKey().getVersion(), exc);
                     apexParametersMap.remove(entry2.getKey());
+                    policyModelsMap.remove(entry2.getKey());
                 }
                 return entry1;
             }));
-        return finalPolicyModelEntry.getValue();
+        AxPolicyModel finalPolicyModel = new AxPolicyModel(finalPolicyModelEntry.getValue());
+        policyModelsMap.put(tempId, tempModel); // put back the original first entry into the policyModelsMap
+        return finalPolicyModel;
     }
 
     private void setUpMarshallerAndUnmarshaller(EngineServiceParameters engineServiceParameters,
@@ -215,7 +227,7 @@ public class ApexActivator {
      * paired marshaler
      * @param inputParametersMap the apex parameters
      */
-    private void setUpmarshalerPairings(Map<String, EventHandlerParameters> inputParametersMap) {
+    private void setUpMarshalerPairings(Map<String, EventHandlerParameters> inputParametersMap) {
         for (final Entry<String, EventHandlerParameters> inputParameters : inputParametersMap.entrySet()) {
             final ApexEventUnmarshaller unmarshaller = unmarshallerMap.get(inputParameters.getKey());
 
@@ -237,21 +249,30 @@ public class ApexActivator {
     }
 
     /**
+     * Updates the APEX Engine with the model created from new Policies.
+     *
+     * @param apexParamsMap  the apex parameters map for the Apex service
+     * @throws ApexException on errors
+     */
+    public void updateModel(Map<ToscaPolicyIdentifier, ApexParameters> apexParamsMap) throws ApexException {
+        try {
+            shutdownMarshallerAndUnmarshaller();
+            ApexParameters apexParameters = apexParamsMap.values().iterator().next();
+            setUpModelMarhsallerAndUnmarshaller(apexParameters);
+        } catch (final Exception e) {
+            LOGGER.debug(APEX_ENGINE_FAILED_MSG, e);
+            throw new ApexActivatorException(APEX_ENGINE_FAILED_MSG, e);
+        }
+    }
+
+    /**
      * Terminate the Apex engine.
      *
      * @throws ApexException on termination errors
      */
     public void terminate() throws ApexException {
         // Shut down all marshalers and unmarshalers
-        for (final ApexEventMarshaller marshaller : marshallerMap.values()) {
-            marshaller.stop();
-        }
-        marshallerMap.clear();
-
-        for (final ApexEventUnmarshaller unmarshaller : unmarshallerMap.values()) {
-            unmarshaller.stop();
-        }
-        unmarshallerMap.clear();
+        shutdownMarshallerAndUnmarshaller();
 
         // Check if the engine service handler has been shut down already
         if (engineServiceHandler != null) {
@@ -263,4 +284,14 @@ public class ApexActivator {
         ModelService.clear();
         ParameterService.clear();
     }
+
+    /**
+     * Shuts down all marshallers and unmarshallers.
+     */
+    private void shutdownMarshallerAndUnmarshaller() {
+        marshallerMap.values().forEach(ApexEventMarshaller::stop);
+        marshallerMap.clear();
+        unmarshallerMap.values().forEach(ApexEventUnmarshaller::stop);
+        unmarshallerMap.clear();
+    }
 }
diff --git a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexMain.java b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexMain.java
index 4600690e7..14b57b2d1 100644
--- a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexMain.java
+++ b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexMain.java
@@ -26,9 +26,15 @@ import java.util.Base64;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.TreeMap;
 import lombok.Getter;
 import lombok.Setter;
 import org.onap.policy.apex.model.basicmodel.concepts.ApexException;
+import org.onap.policy.apex.model.basicmodel.concepts.AxArtifactKey;
+import org.onap.policy.apex.model.basicmodel.service.ModelService;
+import org.onap.policy.apex.model.contextmodel.concepts.AxContextAlbum;
+import org.onap.policy.apex.model.contextmodel.concepts.AxContextAlbums;
+import org.onap.policy.apex.model.policymodel.concepts.AxPolicyModel;
 import org.onap.policy.apex.service.parameters.ApexParameterHandler;
 import org.onap.policy.apex.service.parameters.ApexParameters;
 import org.onap.policy.apex.service.parameters.eventhandler.EventHandlerParameters;
@@ -128,6 +134,67 @@ public class ApexMain {
         LOGGER.exit("Started Apex");
     }
 
+    /**
+     * Updates the APEX Engine with the model created from new Policies.
+     *
+     * @param policyArgsMap the map with command line arguments as value and policy-id as key
+     * @throws ApexException on errors
+     */
+    public void updateModel(Map<ToscaPolicyIdentifier, String[]> policyArgsMap) throws ApexException {
+        apexParametersMap.clear();
+        AxContextAlbums albums = ModelService.getModel(AxContextAlbums.class);
+        Map<AxArtifactKey, AxContextAlbum> albumsMap = new TreeMap<>();
+        for (Entry<ToscaPolicyIdentifier, String[]> policyArgsEntry : policyArgsMap.entrySet()) {
+            findAlbumsToHold(albumsMap, policyArgsEntry.getKey());
+            try {
+                apexParametersMap.put(policyArgsEntry.getKey(), populateApexParameters(policyArgsEntry.getValue()));
+            } catch (ApexException e) {
+                LOGGER.error("Invalid arguments specified for policy - {}:{}", policyArgsEntry.getKey().getName(),
+                    policyArgsEntry.getKey().getVersion(), e);
+            }
+        }
+        try {
+            if (albumsMap.isEmpty()) {
+                // clear context since none of the policies' context albums has to be retained
+                // this could be because all policies have a major version change,
+                // or a full set of new policies are received in the update message
+                activator.terminate();
+                // ParameterService is cleared when activator is terminated. Register the engine parameters in this case
+                new ApexParameterHandler().registerParameters(apexParametersMap.values().iterator().next());
+                activator = new ApexActivator(apexParametersMap);
+                activator.initialize();
+                setAlive(true);
+            } else {
+                albums.setAlbumsMap(albumsMap);
+                activator.setApexParametersMap(apexParametersMap);
+                activator.updateModel(apexParametersMap);
+            }
+        } catch (final ApexException e) {
+            LOGGER.error(APEX_SERVICE_FAILED_MSG, e);
+            activator.terminate();
+            throw new ApexException(e.getMessage());
+        }
+    }
+
+    /**
+     * Find the context albums which should be retained when updating the policies.
+     *
+     * @param albumsMap the albums which should be kept during model update
+     * @param policyId the policy id of current policy
+     */
+    private void findAlbumsToHold(Map<AxArtifactKey, AxContextAlbum> albumsMap, ToscaPolicyIdentifier policyId) {
+        for (Entry<ToscaPolicyIdentifier, AxPolicyModel> policyModelsEntry : activator.getPolicyModelsMap()
+            .entrySet()) {
+            // If a policy with the same major version is received in PDP_UPDATE,
+            // context for that policy has to be retained. For this, take such policies' albums
+            if (policyModelsEntry.getKey().getName().equals(policyId.getName())
+                && policyModelsEntry.getKey().getVersion().split("\\.")[0]
+                    .equals(policyId.getVersion().split("\\.")[0])) {
+                albumsMap.putAll(policyModelsEntry.getValue().getAlbums().getAlbumsMap());
+            }
+        }
+    }
+
     private ApexParameters populateApexParameters(String[] args) throws ApexException {
         // Check the arguments
         final ApexCommandLineArguments arguments = new ApexCommandLineArguments();
diff --git a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineServiceImpl.java b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineServiceImpl.java
index 8247fd5f3..f5e36e864 100644
--- a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineServiceImpl.java
+++ b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineServiceImpl.java
@@ -77,8 +77,8 @@ public final class EngineServiceImpl implements EngineService, EngineServiceEven
     private AxArtifactKey engineServiceKey = null;
 
     // The Apex engine workers this engine service is handling
-    private final Map<AxArtifactKey, EngineService> engineWorkerMap = Collections
-                    .synchronizedMap(new LinkedHashMap<AxArtifactKey, EngineService>());
+    private final Map<AxArtifactKey, EngineWorker> engineWorkerMap = Collections
+                    .synchronizedMap(new LinkedHashMap<AxArtifactKey, EngineWorker>());
 
     // Event queue for events being sent into the Apex engines, it used by all engines within a
     // group.
@@ -342,9 +342,17 @@ public final class EngineServiceImpl implements EngineService, EngineServiceEven
         }
 
         // Update the engines
-        for (final Entry<AxArtifactKey, EngineService> engineWorkerEntry : engineWorkerMap.entrySet()) {
+        boolean isSubsequentInstance = false;
+        for (final Entry<AxArtifactKey, EngineWorker> engineWorkerEntry : engineWorkerMap.entrySet()) {
             LOGGER.info("Registering apex model on engine {}", engineWorkerEntry.getKey().getId());
-            engineWorkerEntry.getValue().updateModel(engineWorkerEntry.getKey(), apexModel, forceFlag);
+            EngineWorker engineWorker = engineWorkerEntry.getValue();
+            if (isSubsequentInstance) {
+                // set subsequentInstance flag as true if the current engine worker instance is not the first one
+                // first engine instance will have this flag as false
+                engineWorker.setSubsequentInstance(true);
+            }
+            engineWorker.updateModel(engineWorkerEntry.getKey(), apexModel, forceFlag);
+            isSubsequentInstance = true;
         }
 
         // start all engines on this engine service if it was not stopped before the update
@@ -355,7 +363,7 @@ public final class EngineServiceImpl implements EngineService, EngineServiceEven
         }
         // Check if all engines are running
         final StringBuilder notRunningEngineIdBuilder = new StringBuilder();
-        for (final Entry<AxArtifactKey, EngineService> engineWorkerEntry : engineWorkerMap.entrySet()) {
+        for (final Entry<AxArtifactKey, EngineWorker> engineWorkerEntry : engineWorkerMap.entrySet()) {
             if (engineWorkerEntry.getValue().getState() != AxEngineState.READY
                             && engineWorkerEntry.getValue().getState() != AxEngineState.EXECUTING) {
                 notRunningEngineIdBuilder.append(engineWorkerEntry.getKey().getId());
@@ -387,7 +395,7 @@ public final class EngineServiceImpl implements EngineService, EngineServiceEven
         }
         // Check if all engines are stopped
         final StringBuilder notStoppedEngineIdBuilder = new StringBuilder();
-        for (final Entry<AxArtifactKey, EngineService> engineWorkerEntry : engineWorkerMap.entrySet()) {
+        for (final Entry<AxArtifactKey, EngineWorker> engineWorkerEntry : engineWorkerMap.entrySet()) {
             if (engineWorkerEntry.getValue().getState() != AxEngineState.STOPPED) {
                 notStoppedEngineIdBuilder.append(engineWorkerEntry.getKey().getId());
                 notStoppedEngineIdBuilder.append('(');
diff --git a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineWorker.java b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineWorker.java
index a24d9618a..e00515bd0 100644
--- a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineWorker.java
+++ b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/runtime/impl/EngineWorker.java
@@ -6,15 +6,15 @@
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *      http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- * 
+ *
  * SPDX-License-Identifier: Apache-2.0
  * ============LICENSE_END=========================================================
  */
@@ -25,7 +25,6 @@ import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonParser;
-
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.util.Arrays;
@@ -33,7 +32,7 @@ import java.util.Collection;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.concurrent.BlockingQueue;
-
+import lombok.Setter;
 import org.onap.policy.apex.context.ContextException;
 import org.onap.policy.apex.context.ContextRuntimeException;
 import org.onap.policy.apex.context.SchemaHelper;
@@ -98,6 +97,9 @@ final class EngineWorker implements EngineService {
     // Converts ApexEvent instances to and from EnEvent instances
     private ApexEvent2EnEventConverter apexEnEventConverter = null;
 
+    @Setter
+    private boolean isSubsequentInstance;
+
     /**
      * Constructor that creates an Apex engine, an event processor for events to be sent to that engine, and an
      * {@link ApexModelReader} instance to read Apex models using JAXB.
@@ -236,9 +238,8 @@ final class EngineWorker implements EngineService {
                 }
             }
         }
-
         // Update the Apex model in the Apex engine
-        engine.updateModel(apexModel);
+        engine.updateModel(apexModel, isSubsequentInstance);
 
         LOGGER.debug("engine model {} added to the engine-{}", apexModel.getKey().getId(), engineWorkerKey);
         LOGGER.exit();
@@ -613,7 +614,7 @@ final class EngineWorker implements EngineService {
 
         /**
          * Debug the event if debug is enabled.
-         * 
+         *
          * @param event the event to debug
          */
         private void debugEventIfDebugEnabled(ApexEvent event) {
diff --git a/services/services-engine/src/main/java/org/onap/policy/apex/service/parameters/ApexParameterHandler.java b/services/services-engine/src/main/java/org/onap/policy/apex/service/parameters/ApexParameterHandler.java
index c1ef50bd7..553ed18c6 100644
--- a/services/services-engine/src/main/java/org/onap/policy/apex/service/parameters/ApexParameterHandler.java
+++ b/services/services-engine/src/main/java/org/onap/policy/apex/service/parameters/ApexParameterHandler.java
@@ -130,10 +130,10 @@ public class ApexParameterHandler {
 
     /**
      * Register all the incoming parameters with the parameter service.
-     * 
+     *
      * @param parameters The parameters to register
      */
-    private void registerParameters(ApexParameters parameters) {
+    public void registerParameters(ApexParameters parameters) {
         ParameterService.register(parameters);
         ParameterService.register(parameters.getEngineServiceParameters());
         ParameterService.register(parameters.getEngineServiceParameters().getEngineParameters());
diff --git a/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/ApexEngineHandler.java b/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/ApexEngineHandler.java
index 1953939b7..6a5bb17ff 100644
--- a/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/ApexEngineHandler.java
+++ b/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/ApexEngineHandler.java
@@ -56,6 +56,35 @@ public class ApexEngineHandler {
      * @throws ApexStarterException if the apex engine instantiation failed using the policies passed
      */
     public ApexEngineHandler(List<ToscaPolicy> policies)  throws ApexStarterException {
+        Map<ToscaPolicyIdentifier, String[]> policyArgsMap = createPolicyArgsMap(policies);
+        LOGGER.debug("Starting apex engine.");
+        try {
+            apexMain = new ApexMain(policyArgsMap);
+        } catch (ApexException e) {
+            throw new ApexStarterException(e);
+        }
+    }
+
+    /**
+     * Updates the Apex Engine with the policy model created from new list of policies.
+     *
+     * @param policies the list of policies
+     * @throws ApexStarterException if the apex engine instantiation failed using the policies passed
+     */
+    public void updateApexEngine(List<ToscaPolicy> policies) throws ApexStarterException {
+        if (null == apexMain || !apexMain.isAlive()) {
+            throw new ApexStarterException("Apex Engine not initialized.");
+        }
+        Map<ToscaPolicyIdentifier, String[]> policyArgsMap = createPolicyArgsMap(policies);
+        try {
+            apexMain.updateModel(policyArgsMap);
+        } catch (ApexException e) {
+            throw new ApexStarterException(e);
+        }
+    }
+
+    private Map<ToscaPolicyIdentifier, String[]> createPolicyArgsMap(List<ToscaPolicy> policies)
+        throws ApexStarterException {
         Map<ToscaPolicyIdentifier, String[]> policyArgsMap = new LinkedHashMap<>();
         for (ToscaPolicy policy : policies) {
             Object properties = policy.getProperties().get("content");
@@ -78,13 +107,7 @@ public class ApexEngineHandler {
             final String[] apexArgs = { "-c", apexConfigFilePath, "-m", modelFilePath };
             policyArgsMap.put(policy.getIdentifier(), apexArgs);
         }
-
-        LOGGER.debug("Starting apex engine.");
-        try {
-            apexMain = new ApexMain(policyArgsMap);
-        } catch (ApexException e) {
-            throw new ApexStarterException(e);
-        }
+        return policyArgsMap;
     }
 
     /**
diff --git a/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/PdpUpdateMessageHandler.java b/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/PdpUpdateMessageHandler.java
index ecc0bec21..33ac81f5d 100644
--- a/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/PdpUpdateMessageHandler.java
+++ b/services/services-onappf/src/main/java/org/onap/policy/apex/services/onappf/handler/PdpUpdateMessageHandler.java
@@ -162,10 +162,11 @@ public class PdpUpdateMessageHandler {
         PdpResponseDetails pdpResponseDetails = null;
         try {
             if (null != apexEngineHandler && apexEngineHandler.isApexEngineRunning()) {
-                apexEngineHandler.shutdown();
+                apexEngineHandler.updateApexEngine(pdpUpdateMsg.getPolicies());
+            } else {
+                apexEngineHandler = new ApexEngineHandler(pdpUpdateMsg.getPolicies());
+                Registry.registerOrReplace(ApexStarterConstants.REG_APEX_ENGINE_HANDLER, apexEngineHandler);
             }
-            apexEngineHandler = new ApexEngineHandler(pdpUpdateMsg.getPolicies());
-            Registry.registerOrReplace(ApexStarterConstants.REG_APEX_ENGINE_HANDLER, apexEngineHandler);
             if (apexEngineHandler.isApexEngineRunning()) {
                 List<ToscaPolicyIdentifier> runningPolicies = apexEngineHandler.getRunningPolicies();
                 if (new HashSet<>(runningPolicies)