Improve handling of multiple policy in APEX PDP

Change-Id: Ic4adf5bd8876dc31fc93993298e90389baaa2c39
Issue-ID: POLICY-2883
Signed-off-by: a.sreekumar <ajith.sreekumar@bell.ca>

8 files changed, 907 insertions, 357 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 cadcc7ee8..3451c120c 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
@@ -2,7 +2,7 @@
  * ============LICENSE_START=======================================================
  *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
  *  Modifications Copyright (C) 2019-2021 Nordix Foundation.
- *  Modifications Copyright (C) 2020 Bell Canada. All rights reserved.
+ *  Modifications Copyright (C) 2020-2021 Bell Canada. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,35 +22,41 @@
 
 package org.onap.policy.apex.service.engine.main;
 
-import java.util.AbstractMap;
-import java.util.ArrayList;
 import java.util.LinkedHashMap;
-import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
-import java.util.Optional;
-import java.util.Set;
-import java.util.stream.Collectors;
 import lombok.Getter;
 import lombok.Setter;
 import org.onap.policy.apex.model.basicmodel.concepts.ApexException;
 import org.onap.policy.apex.model.basicmodel.concepts.ApexRuntimeException;
 import org.onap.policy.apex.model.basicmodel.concepts.AxArtifactKey;
+import org.onap.policy.apex.model.basicmodel.concepts.AxKeyInfo;
+import org.onap.policy.apex.model.basicmodel.concepts.AxKeyInformation;
 import org.onap.policy.apex.model.basicmodel.handling.ApexModelException;
 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.contextmodel.concepts.AxContextSchema;
+import org.onap.policy.apex.model.contextmodel.concepts.AxContextSchemas;
 import org.onap.policy.apex.model.enginemodel.concepts.AxEngineModel;
+import org.onap.policy.apex.model.eventmodel.concepts.AxEvent;
+import org.onap.policy.apex.model.eventmodel.concepts.AxEvents;
+import org.onap.policy.apex.model.policymodel.concepts.AxPolicies;
+import org.onap.policy.apex.model.policymodel.concepts.AxPolicy;
 import org.onap.policy.apex.model.policymodel.concepts.AxPolicyModel;
+import org.onap.policy.apex.model.policymodel.concepts.AxTask;
+import org.onap.policy.apex.model.policymodel.concepts.AxTasks;
 import org.onap.policy.apex.model.policymodel.handling.PolicyModelMerger;
 import org.onap.policy.apex.service.engine.event.ApexEventException;
 import org.onap.policy.apex.service.engine.runtime.EngineService;
 import org.onap.policy.apex.service.engine.runtime.impl.EngineServiceImpl;
+import org.onap.policy.apex.service.parameters.ApexParameterConstants;
 import org.onap.policy.apex.service.parameters.ApexParameters;
 import org.onap.policy.apex.service.parameters.engineservice.EngineServiceParameters;
 import org.onap.policy.apex.service.parameters.eventhandler.EventHandlerParameters;
 import org.onap.policy.apex.service.parameters.eventhandler.EventHandlerPeeredMode;
 import org.onap.policy.common.parameters.ParameterService;
-import org.onap.policy.models.tosca.authorative.concepts.ToscaConceptIdentifier;
 import org.slf4j.ext.XLogger;
 import org.slf4j.ext.XLoggerFactory;
 
@@ -66,13 +72,12 @@ public class ApexActivator {
     // The logger for this class
     private static final XLogger LOGGER = XLoggerFactory.getXLogger(ApexActivator.class);
 
-    // The parameters of the Apex activator when running with multiple policies
     @Getter
     @Setter
-    private Map<ToscaConceptIdentifier, ApexParameters> apexParametersMap;
+    private ApexParameters apexParameters;
 
     @Getter
-    Map<ToscaConceptIdentifier, AxPolicyModel> policyModelsMap;
+    private AxPolicyModel policyModel;
 
     // Event unmarshalers are used to receive events asynchronously into Apex
     private final Map<String, ApexEventUnmarshaller> unmarshallerMap = new LinkedHashMap<>();
@@ -93,10 +98,10 @@ public class ApexActivator {
     /**
      * Instantiate the activator for the Apex engine as a complete service.
      *
-     * @param parametersMap the apex parameters map for the Apex service
+     * @param parameters the apex parameters for the Apex service
      */
-    public ApexActivator(Map<ToscaConceptIdentifier, ApexParameters> parametersMap) {
-        apexParametersMap = parametersMap;
+    public ApexActivator(ApexParameters parameters) {
+        apexParameters = parameters;
     }
 
     /**
@@ -108,96 +113,131 @@ public class ApexActivator {
         LOGGER.debug("Apex engine starting as a service . . .");
 
         try {
-            ApexParameters apexParameters = apexParametersMap.values().iterator().next();
-            // totalInstanceCount is the sum of instance counts required as per each policy
-            int totalInstanceCount = apexParametersMap.values().stream()
-                .mapToInt(p -> p.getEngineServiceParameters().getInstanceCount()).sum();
-            apexParameters.getEngineServiceParameters().setInstanceCount(totalInstanceCount);
-            engineKey = apexParameters.getEngineServiceParameters().getEngineKey();
             instantiateEngine(apexParameters);
             setUpModelMarshallerAndUnmarshaller(apexParameters);
         } catch (final Exception e) {
-            LOGGER.debug(APEX_ENGINE_FAILED_MSG, e);
+            try {
+                terminate();
+            } catch (ApexException e1) {
+                LOGGER.error("Terminating the ApexActivator encountered error", e1);
+            }
             throw new ApexActivatorException(APEX_ENGINE_FAILED_MSG, e);
         }
 
         LOGGER.debug("Apex engine started as a service");
     }
 
-    private void setUpModelMarshallerAndUnmarshaller(ApexParameters apexParameters) throws ApexException {
-        policyModelsMap = new LinkedHashMap<>();
-        Map<String, EventHandlerParameters> inputParametersMap = new LinkedHashMap<>();
-        Map<String, EventHandlerParameters> outputParametersMap = new LinkedHashMap<>();
-        Set<Entry<ToscaConceptIdentifier, ApexParameters>> apexParamsEntrySet = new LinkedHashSet<>(
-            apexParametersMap.entrySet());
-        apexParamsEntrySet.stream().forEach(apexParamsEntry -> {
-            ApexParameters apexParams = apexParamsEntry.getValue();
-            List<String> duplicateInputParameters = new ArrayList<>(apexParams.getEventInputParameters().keySet());
-            duplicateInputParameters.retainAll(inputParametersMap.keySet());
-            List<String> duplicateOutputParameters = new ArrayList<>(apexParams.getEventOutputParameters().keySet());
-            duplicateOutputParameters.retainAll(outputParametersMap.keySet());
-
-            if (!(duplicateInputParameters.isEmpty() && duplicateOutputParameters.isEmpty())) {
-                LOGGER.error("I/O Parameters {}/{} for {}:{} are duplicates. So this policy is not executed.",
-                    duplicateInputParameters, duplicateOutputParameters, apexParamsEntry.getKey().getName(),
-                    apexParamsEntry.getKey().getVersion());
-                apexParametersMap.remove(apexParamsEntry.getKey());
-                return;
-            }
 
-            inputParametersMap.putAll(apexParams.getEventInputParameters());
-            outputParametersMap.putAll(apexParams.getEventOutputParameters());
-            // Check if a policy model file has been specified
-            if (apexParams.getEngineServiceParameters().getPolicyModel() != null) {
-                LOGGER.debug("deploying policy model to the apex engines . . .");
-                try {
-                    final String policyModelString = apexParams.getEngineServiceParameters().getPolicyModel();
-                    AxPolicyModel policyModel = EngineServiceImpl.createModel(engineKey, policyModelString);
-                    policyModelsMap.put(apexParamsEntry.getKey(), policyModel);
-                } catch (ApexException e) {
-                    throw new ApexRuntimeException("Failed to create the apex model.", e);
-                }
-            }
-        });
-        AxPolicyModel finalPolicyModel = aggregatePolicyModels(policyModelsMap);
+    private void instantiateEngine(ApexParameters apexParameters) throws ApexException {
+        if (null != apexEngineService && apexEngineService.getKey().equals(engineKey)) {
+            throw new ApexException("Apex Engine already initialized.");
+        }
+        // Create engine with specified thread count
+        LOGGER.debug("starting apex engine service . . .");
+        apexEngineService = EngineServiceImpl.create(apexParameters.getEngineServiceParameters());
+
+        // Create the engine holder to hold the engine's references and act as an event
+        // receiver
+        engineServiceHandler = new ApexEngineServiceHandler(apexEngineService);
+    }
+
+    private void setUpModelMarshallerAndUnmarshaller(ApexParameters apexParameters) throws ApexException {
+        AxPolicyModel model;
+        try {
+            final String policyModelString = apexParameters.getEngineServiceParameters().getPolicyModel();
+            model = EngineServiceImpl.createModel(apexParameters.getEngineServiceParameters().getEngineKey(),
+                policyModelString);
+        } catch (ApexException e) {
+            throw new ApexRuntimeException("Failed to create the apex model.", e);
+        }
 
+        AxKeyInformation existingKeyInformation = null;
+        AxContextSchemas existingSchemas = null;
+        AxEvents existingEvents = null;
+        AxContextAlbums existingAlbums = null;
+        AxTasks existingTasks = null;
+        AxPolicies existingPolicies = null;
+        if (ModelService.existsModel(AxPolicyModel.class)) {
+            existingKeyInformation = new AxKeyInformation(ModelService.getModel(AxKeyInformation.class));
+            existingSchemas = new AxContextSchemas(ModelService.getModel(AxContextSchemas.class));
+            existingEvents = new AxEvents(ModelService.getModel(AxEvents.class));
+            existingAlbums = new AxContextAlbums(ModelService.getModel(AxContextAlbums.class));
+            existingTasks = new AxTasks(ModelService.getModel(AxTasks.class));
+            existingPolicies = new AxPolicies(ModelService.getModel(AxPolicies.class));
+        }
         // Set the policy model in the engine
-        apexEngineService.updateModel(engineKey, finalPolicyModel, true);
+        try {
+            apexEngineService.updateModel(apexParameters.getEngineServiceParameters().getEngineKey(), model, true);
+            policyModel = new AxPolicyModel(model);
+        } catch (ApexException exp) {
+            // Discard concepts from the current policy
+            if (null != existingKeyInformation) {
+                // Update model service with other policies' concepts.
+                ModelService.registerModel(AxKeyInformation.class, existingKeyInformation);
+                ModelService.registerModel(AxContextSchemas.class, existingSchemas);
+                ModelService.registerModel(AxEvents.class, existingEvents);
+                ModelService.registerModel(AxContextAlbums.class, existingAlbums);
+                ModelService.registerModel(AxTasks.class, existingTasks);
+                ModelService.registerModel(AxPolicies.class, existingPolicies);
+            } else {
+                ModelService.clear();
+            }
+            throw exp;
+        }
+        if (null != existingKeyInformation) {
+            // Make sure all concepts in previously deployed policies are retained in ModelService
+            // during multi policy deployment.
+            updateModelService(existingKeyInformation, existingSchemas, existingEvents, existingAlbums, existingTasks,
+                existingPolicies);
+        }
 
-        handleExistingMarshallerAndUnmarshaller(inputParametersMap, outputParametersMap);
-        setUpNewMarshallerAndUnmarshaller(apexParameters.getEngineServiceParameters(), inputParametersMap,
-            outputParametersMap);
+        setUpNewMarshallerAndUnmarshaller(apexParameters.getEngineServiceParameters(),
+            apexParameters.getEventInputParameters(), apexParameters.getEventOutputParameters());
 
         // Wire up pairings between marhsallers and unmarshallers
-        setUpMarshalerPairings(inputParametersMap);
+        setUpMarshalerPairings(apexParameters.getEventInputParameters());
 
         // Start event processing
-        startUnmarshallers(inputParametersMap);
+        startUnmarshallers(apexParameters.getEventInputParameters());
     }
 
-    private AxPolicyModel aggregatePolicyModels(Map<ToscaConceptIdentifier, AxPolicyModel> policyModelsMap) {
-        // Doing a deep copy so that original values in policyModelsMap is retained
-        // after reduction operation
-        Set<Entry<ToscaConceptIdentifier, AxPolicyModel>> policyModelsEntries = policyModelsMap.entrySet().stream()
-            .map(entry -> new AbstractMap.SimpleEntry<>(entry.getKey(), entry.getValue())).collect(Collectors.toSet());
-        Optional<Entry<ToscaConceptIdentifier, AxPolicyModel>> finalPolicyModelEntry = policyModelsEntries.stream()
-            .reduce((entry1, entry2) -> {
-                try {
-                    entry1.setValue(
-                        PolicyModelMerger.getMergedPolicyModel(entry1.getValue(), entry2.getValue(), true, true));
-                } catch (ApexModelException exc) {
-                    LOGGER.error("Policy model for {} : {} has duplicates. So this policy is not executed.",
-                        entry2.getKey().getName(), entry2.getKey().getVersion(), exc);
-                    apexParametersMap.remove(entry2.getKey());
-                    policyModelsMap.remove(entry2.getKey());
-                }
-                return entry1;
-            });
-        AxPolicyModel finalPolicyModel = null;
-        if (finalPolicyModelEntry.isPresent()) {
-            finalPolicyModel = new AxPolicyModel(finalPolicyModelEntry.get().getValue());
+    private void updateModelService(AxKeyInformation existingKeyInformation,
+        AxContextSchemas existingSchemas, AxEvents existingEvents,
+        AxContextAlbums existingAlbums, AxTasks existingTasks,
+        AxPolicies existingPolicies) throws ApexModelException {
+
+        AxContextSchemas axContextSchemas = ModelService.getModel(AxContextSchemas.class);
+        AxEvents axEvents = ModelService.getModel(AxEvents.class);
+        AxContextAlbums axContextAlbums = ModelService.getModel(AxContextAlbums.class);
+        AxTasks axTasks = ModelService.getModel(AxTasks.class);
+        AxPolicies axPolicies = ModelService.getModel(AxPolicies.class);
+
+        Map<AxArtifactKey, AxContextSchema> newSchemasMap = axContextSchemas.getSchemasMap();
+        Map<AxArtifactKey, AxEvent> newEventsMap = axEvents.getEventMap();
+        Map<AxArtifactKey, AxContextAlbum> newAlbumsMap = axContextAlbums.getAlbumsMap();
+        Map<AxArtifactKey, AxTask> newTasksMap = axTasks.getTaskMap();
+        Map<AxArtifactKey, AxPolicy> newPoliciesMap = axPolicies.getPolicyMap();
+
+        StringBuilder errorMessage = new StringBuilder();
+        PolicyModelMerger.checkForDuplicateItem(existingSchemas.getSchemasMap(), newSchemasMap, errorMessage, "schema");
+        PolicyModelMerger.checkForDuplicateItem(existingEvents.getEventMap(), newEventsMap, errorMessage, "event");
+        PolicyModelMerger.checkForDuplicateItem(existingAlbums.getAlbumsMap(), newAlbumsMap, errorMessage, "album");
+        PolicyModelMerger.checkForDuplicateItem(existingTasks.getTaskMap(), newTasksMap, errorMessage, "task");
+        PolicyModelMerger.checkForDuplicateItem(existingPolicies.getPolicyMap(), newPoliciesMap, errorMessage,
+            "policy");
+        if (errorMessage.length() > 0) {
+            throw new ApexModelException(errorMessage.toString());
         }
-        return finalPolicyModel;
+
+        AxKeyInformation axKeyInformation = ModelService.getModel(AxKeyInformation.class);
+        Map<AxArtifactKey, AxKeyInfo> newKeyInfoMap = axKeyInformation.getKeyInfoMap();
+        // Now add all the concepts that must be copied over
+        newKeyInfoMap.putAll(existingKeyInformation.getKeyInfoMap());
+        newSchemasMap.putAll(existingSchemas.getSchemasMap());
+        newEventsMap.putAll(existingEvents.getEventMap());
+        newAlbumsMap.putAll(existingAlbums.getAlbumsMap());
+        newTasksMap.putAll(existingTasks.getTaskMap());
+        newPoliciesMap.putAll(existingPolicies.getPolicyMap());
     }
 
     private void setUpNewMarshallerAndUnmarshaller(EngineServiceParameters engineServiceParameters,
@@ -226,38 +266,6 @@ public class ApexActivator {
         }
     }
 
-    private void handleExistingMarshallerAndUnmarshaller(Map<String, EventHandlerParameters> inputParametersMap,
-        Map<String, EventHandlerParameters> outputParametersMap) {
-        // stop and remove any marshaller/unmarshaller that is part of a policy that is
-        // undeployed
-        marshallerMap.entrySet().stream()
-            .filter(marshallerEntry -> !outputParametersMap.containsKey(marshallerEntry.getKey()))
-            .forEach(marshallerEntry -> marshallerEntry.getValue().stop());
-        marshallerMap.keySet().removeIf(marshallerKey -> !outputParametersMap.containsKey(marshallerKey));
-        unmarshallerMap.entrySet().stream()
-            .filter(unmarshallerEntry -> !inputParametersMap.containsKey(unmarshallerEntry.getKey()))
-            .forEach(unmarshallerEntry -> unmarshallerEntry.getValue().stop());
-        unmarshallerMap.keySet().removeIf(unmarshallerKey -> !inputParametersMap.containsKey(unmarshallerKey));
-
-        // If a marshaller/unmarshaller is already initialized, they don't need to be
-        // reinitialized during model update.
-        outputParametersMap.keySet().removeIf(marshallerMap::containsKey);
-        inputParametersMap.keySet().removeIf(unmarshallerMap::containsKey);
-    }
-
-    private void instantiateEngine(ApexParameters apexParameters) throws ApexException {
-        if (null != apexEngineService && apexEngineService.getKey().equals(engineKey)) {
-            throw new ApexException("Apex Engine already initialized.");
-        }
-        // Create engine with specified thread count
-        LOGGER.debug("starting apex engine service . . .");
-        apexEngineService = EngineServiceImpl.create(apexParameters.getEngineServiceParameters());
-
-        // Create the engine holder to hold the engine's references and act as an event
-        // receiver
-        engineServiceHandler = new ApexEngineServiceHandler(apexEngineService);
-    }
-
     /**
      * Set up unmarshaler/marshaler pairing for synchronized event handling. We only
      * need to traverse the unmarshalers because the unmarshalers and marshalers are
@@ -275,8 +283,8 @@ public class ApexActivator {
                 // Check if the unmarshaler is synchronized with a marshaler
                 if (inputParameters.getValue().isPeeredMode(peeredMode)) {
                     // Find the unmarshaler and marshaler
-                    final ApexEventMarshaller peeredMarshaler = marshallerMap
-                        .get(inputParameters.getValue().getPeer(peeredMode));
+                    final ApexEventMarshaller peeredMarshaler =
+                        marshallerMap.get(inputParameters.getValue().getPeer(peeredMode));
 
                     // Connect the unmarshaler and marshaler
                     unmarshaller.connectMarshaler(peeredMode, peeredMarshaler);
@@ -298,22 +306,6 @@ 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<ToscaConceptIdentifier, ApexParameters> apexParamsMap) throws ApexException {
-        try {
-            ApexParameters apexParameters = apexParamsMap.values().iterator().next();
-            setUpModelMarshallerAndUnmarshaller(apexParameters);
-        } catch (final Exception e) {
-            LOGGER.debug(APEX_ENGINE_FAILED_MSG, e);
-            throw new ApexActivatorException(APEX_ENGINE_FAILED_MSG, e);
-        }
-    }
-
-    /**
      * Get the Apex engine worker stats.
      */
     public List<AxEngineModel> getEngineStats() {
@@ -338,19 +330,25 @@ public class ApexActivator {
             engineServiceHandler.terminate();
             engineServiceHandler = null;
         }
-
-        // Clear the services
-        ModelService.clear();
-        ParameterService.clear();
+        // Clear the services in case if this was the only policy running in the engine
+        ApexParameters apexParams = null;
+        if (ParameterService.contains(ApexParameterConstants.MAIN_GROUP_NAME)) {
+            apexParams = ParameterService.get(ApexParameterConstants.MAIN_GROUP_NAME);
+        }
+        if (null != apexParams
+            && apexParameters.getEventInputParameters().size() == apexParams.getEventInputParameters().size()) {
+            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();
+        marshallerMap.values().forEach(ApexEventMarshaller::stop);
+        marshallerMap.clear();
     }
 }
diff --git a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexEventUnmarshaller.java b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexEventUnmarshaller.java
index fd6ac4489..fdc404c67 100644
--- a/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexEventUnmarshaller.java
+++ b/services/services-engine/src/main/java/org/onap/policy/apex/service/engine/main/ApexEventUnmarshaller.java
@@ -2,7 +2,7 @@
  * ============LICENSE_START=======================================================
  *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
  *  Modifications Copyright (C) 2019-2020 Nordix Foundation.
- *  Modifications Copyright (C) 2020 Bell Canada. All rights reserved.
+ *  Modifications Copyright (C) 2020-2021 Bell Canada. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -347,17 +347,16 @@ public class ApexEventUnmarshaller implements ApexEventReceiver, Runnable {
         // Order the stop
         stopOrderedFlag = true;
 
-        // Order a stop on the synchronous cache if one exists
-        if (consumerParameters != null && consumerParameters.isPeeredMode(EventHandlerPeeredMode.SYNCHRONOUS)
-            && consumer.getPeeredReference(EventHandlerPeeredMode.SYNCHRONOUS) != null) {
-            ((SynchronousEventCache) consumer.getPeeredReference(EventHandlerPeeredMode.SYNCHRONOUS)).stop();
-        }
-
         // Wait for thread shutdown
         while (unmarshallerThread != null && unmarshallerThread.isAlive()) {
             ThreadUtilities.sleep(UNMARSHALLER_SHUTDOWN_WAIT_INTERVAL);
         }
 
+        // Order a stop on the synchronous cache if one exists
+        if (consumerParameters != null && consumerParameters.isPeeredMode(EventHandlerPeeredMode.SYNCHRONOUS)
+            && consumer.getPeeredReference(EventHandlerPeeredMode.SYNCHRONOUS) != null) {
+            ((SynchronousEventCache) consumer.getPeeredReference(EventHandlerPeeredMode.SYNCHRONOUS)).stop();
+        }
         LOGGER.exit("shut down Apex event unmarshaller");
     }
 }
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 5707c95ad..65c2acffa 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
@@ -2,7 +2,7 @@
  * ============LICENSE_START=======================================================
  *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
  *  Modification Copyright (C) 2019-2021 Nordix Foundation.
- *  Modifications Copyright (C) 2020 Bell Canada. All rights reserved.
+ *  Modifications Copyright (C) 2020-2021 Bell Canada. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,26 +24,20 @@ package org.onap.policy.apex.service.engine.main;
 
 import java.util.Arrays;
 import java.util.Base64;
-import java.util.LinkedHashMap;
 import java.util.List;
-import java.util.Map;
 import java.util.Map.Entry;
-import java.util.TreeMap;
+import java.util.stream.Collectors;
 import lombok.Getter;
 import lombok.Setter;
 import org.onap.policy.apex.core.engine.EngineParameters;
 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.enginemodel.concepts.AxEngineModel;
-import org.onap.policy.apex.model.policymodel.concepts.AxPolicyModel;
+import org.onap.policy.apex.service.parameters.ApexParameterConstants;
 import org.onap.policy.apex.service.parameters.ApexParameterHandler;
 import org.onap.policy.apex.service.parameters.ApexParameters;
+import org.onap.policy.apex.service.parameters.engineservice.EngineServiceParameters;
 import org.onap.policy.apex.service.parameters.eventhandler.EventHandlerParameters;
 import org.onap.policy.common.parameters.ParameterService;
-import org.onap.policy.models.tosca.authorative.concepts.ToscaConceptIdentifier;
 import org.slf4j.ext.XLogger;
 import org.slf4j.ext.XLoggerFactory;
 
@@ -58,14 +52,12 @@ public class ApexMain {
     private static final XLogger LOGGER = XLoggerFactory.getXLogger(ApexMain.class);
 
     // The Apex Activator that activates the Apex engine
+    @Getter
     private ApexActivator activator;
 
     // The parameters read in from JSON for each policy
     @Getter
-    private Map<ToscaConceptIdentifier, ApexParameters> apexParametersMap;
-
-    //engineParameters are aggregated in case of multiple policies
-    private EngineParameters aggregatedEngineParameters;
+    private ApexParameters apexParameters;
 
     private ApexParameterHandler apexParameterHandler = new ApexParameterHandler();
 
@@ -77,73 +69,27 @@ public class ApexMain {
      * Instantiates the Apex service.
      *
      * @param args the command line arguments
+     * @throws ApexException the apex exception.
      */
-    public ApexMain(final String[] args) {
+    public ApexMain(final String[] args) throws ApexException {
         LOGGER.entry("Starting Apex service with parameters " + Arrays.toString(args) + " . . .");
-        apexParametersMap = new LinkedHashMap<>();
-        aggregatedEngineParameters = new EngineParameters();
         try {
-            apexParametersMap.put(new ToscaConceptIdentifier(), populateApexParameters(args));
+            apexParameters = populateApexParameters(args);
         } catch (ApexException e) {
             LOGGER.error(APEX_SERVICE_FAILED_MSG, e);
             return;
         }
-        apexParameterHandler.registerParameters(apexParametersMap.values().iterator().next());
-        // Now, create the activator for the Apex service
-        activator = new ApexActivator(apexParametersMap);
-
-        // Start the activator
-        try {
-            activator.initialize();
-            setAlive(true);
-        } catch (final ApexActivatorException e) {
-            LOGGER.error("start of Apex service failed, used parameters are " + Arrays.toString(args), e);
-            return;
-        }
-
-        // Add a shutdown hook to shut everything down in an orderly manner
-        Runtime.getRuntime().addShutdownHook(new ApexMainShutdownHookClass());
-        LOGGER.exit("Started Apex");
-    }
-
-    /**
-     * Instantiates the Apex service for multiple policies.
-     *
-     * @param policyArgumentsMap the map with command line arguments as value and policy-id as key
-     * @throws ApexException on errors
-     */
-    public ApexMain(Map<ToscaConceptIdentifier, String[]> policyArgumentsMap) throws ApexException {
-        apexParametersMap = new LinkedHashMap<>();
-        aggregatedEngineParameters = new EngineParameters();
-        for (Entry<ToscaConceptIdentifier, String[]> policyArgsEntry: policyArgumentsMap.entrySet()) {
-            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);
-            }
-        }
-        if (apexParametersMap.isEmpty()) {
-            LOGGER.error(APEX_SERVICE_FAILED_MSG);
-            return;
-        }
+        aggregateParametersAndRegister();
 
-        // Set the aggregated engineParameters which will be used later while creating the engine
-        ApexParameters apexParameters = apexParametersMap.values().iterator().next();
-        apexParameters.getEngineServiceParameters().setEngineParameters(aggregatedEngineParameters);
-        apexParameterHandler.registerParameters(apexParameters);
         // Now, create the activator for the Apex service
-        activator = new ApexActivator(apexParametersMap);
+        activator = new ApexActivator(apexParameters);
 
         // Start the activator
         try {
             activator.initialize();
-            apexParametersMap = activator.getApexParametersMap();
             setAlive(true);
         } catch (final ApexActivatorException e) {
-            LOGGER.error(APEX_SERVICE_FAILED_MSG, e);
-            activator.terminate();
-            return;
+            throw new ApexException("start of Apex service failed, used parameters are " + Arrays.toString(args), e);
         }
 
         // Add a shutdown hook to shut everything down in an orderly manner
@@ -151,75 +97,6 @@ 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<ToscaConceptIdentifier, String[]> policyArgsMap) throws ApexException {
-        // flag that determines if any policy received in PDP_UPDATE is already deployed in the engine
-        boolean isAnyPolicyDeployed = policyArgsMap.keySet().stream().anyMatch(apexParametersMap::containsKey);
-        apexParametersMap.clear();
-        aggregatedEngineParameters = new EngineParameters();
-        AxContextAlbums albums = ModelService.getModel(AxContextAlbums.class);
-        Map<AxArtifactKey, AxContextAlbum> albumsMap = new TreeMap<>();
-        for (Entry<ToscaConceptIdentifier, 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);
-            }
-        }
-        // Set the aggregated engineParameters
-        ApexParameters apexParameters = apexParametersMap.values().iterator().next();
-        apexParameters.getEngineServiceParameters().setEngineParameters(aggregatedEngineParameters);
-        ParameterService.clear();
-        apexParameterHandler.registerParameters(apexParameters);
-        try {
-            if (albumsMap.isEmpty() && !isAnyPolicyDeployed) {
-                // 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 parameters again in this case
-                apexParameterHandler.registerParameters(apexParameters);
-                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, ToscaConceptIdentifier policyId) {
-        for (Entry<ToscaConceptIdentifier, 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();
@@ -263,11 +140,32 @@ public class ApexMain {
                 ehParameterEntry.getValue().setName(ehParameterEntry.getKey());
             }
         }
-        aggregateEngineParameters(axParameters.getEngineServiceParameters().getEngineParameters());
         return axParameters;
     }
 
-    private void aggregateEngineParameters(EngineParameters engineParameters) {
+    private void aggregateParametersAndRegister() throws ApexException {
+        ApexParameters aggregatedParameters = null;
+        if (ParameterService.contains(ApexParameterConstants.MAIN_GROUP_NAME)) {
+            aggregatedParameters = ParameterService.get(ApexParameterConstants.MAIN_GROUP_NAME);
+        } else {
+            aggregatedParameters = new ApexParameters();
+            aggregatedParameters.setEngineServiceParameters(new EngineServiceParameters());
+            apexParameterHandler.registerParameters(aggregatedParameters);
+        }
+        List<String> duplicateInputParameters = aggregatedParameters.getEventInputParameters().keySet().stream()
+            .filter(apexParameters.getEventInputParameters()::containsKey).collect(Collectors.toList());
+        List<String> duplicateOutputParameters = aggregatedParameters.getEventOutputParameters().keySet().stream()
+            .filter(apexParameters.getEventOutputParameters()::containsKey).collect(Collectors.toList());
+        if (!(duplicateInputParameters.isEmpty() && duplicateOutputParameters.isEmpty())) {
+            throw new ApexException(
+                "start of Apex service failed because this policy has the following duplicate I/O parameters: "
+                    + duplicateInputParameters + "/" + duplicateOutputParameters);
+        }
+        aggregatedParameters.getEventInputParameters().putAll(apexParameters.getEventInputParameters());
+        aggregatedParameters.getEventOutputParameters().putAll(apexParameters.getEventOutputParameters());
+        EngineParameters aggregatedEngineParameters =
+            aggregatedParameters.getEngineServiceParameters().getEngineParameters();
+        EngineParameters engineParameters = apexParameters.getEngineServiceParameters().getEngineParameters();
         aggregatedEngineParameters.getTaskParameters().addAll(engineParameters.getTaskParameters());
         aggregatedEngineParameters.getExecutorParameterMap().putAll(engineParameters.getExecutorParameterMap());
         aggregatedEngineParameters.getContextParameters().getSchemaParameters().getSchemaHelperParameterMap()
@@ -346,8 +244,9 @@ public class ApexMain {
      * The main method.
      *
      * @param args the arguments
+     * @throws ApexException the apex exception.
      */
-    public static void main(final String[] args) {
+    public static void main(final String[] args) throws ApexException {
         new ApexMain(args);
     }
 }
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 9a07b4ad5..673d9cab5 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
@@ -2,7 +2,7 @@
  * ============LICENSE_START=======================================================
  *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
  *  Modifications Copyright (C) 2019 Nordix Foundation.
- *  Modifications Copyright (C) 2020 Bell Canada. All rights reserved.
+ *  Modifications Copyright (C) 2020-2021 Bell Canada. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -73,8 +73,6 @@ public class ApexParameterHandler {
      */
     public ApexParameters getParameters(final ApexCommandLineArguments arguments) throws ParameterException {
 
-        ParameterService.clear();
-
         ApexParameters parameters = null;
         String toscaPolicyFilePath = arguments.getToscaPolicyFilePath();
         // Read the parameters
diff --git a/services/services-engine/src/test/java/org/onap/policy/apex/service/engine/main/ApexMainTest.java b/services/services-engine/src/test/java/org/onap/policy/apex/service/engine/main/ApexMainTest.java
index 68472d4de..2cb12c397 100644
--- a/services/services-engine/src/test/java/org/onap/policy/apex/service/engine/main/ApexMainTest.java
+++ b/services/services-engine/src/test/java/org/onap/policy/apex/service/engine/main/ApexMainTest.java
@@ -2,7 +2,7 @@
  * ============LICENSE_START=======================================================
  *  Copyright (C) 2018 Ericsson. All rights reserved.
  *  Modifications Copyright (C) 2020-2021 Nordix Foundation.
- *  Modifications Copyright (C) 2020 Bell Canada. All rights reserved.
+ *  Modifications Copyright (C) 2020-2021 Bell Canada. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,21 +23,22 @@
 package org.onap.policy.apex.service.engine.main;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.awaitility.Awaitility.await;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
 
 import java.io.ByteArrayOutputStream;
 import java.io.OutputStream;
 import java.io.PrintStream;
-import java.util.HashMap;
-import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import org.junit.After;
 import org.junit.Test;
 import org.onap.policy.apex.model.basicmodel.concepts.ApexException;
-import org.onap.policy.apex.service.parameters.ApexParameters;
-import org.onap.policy.models.tosca.authorative.concepts.ToscaConceptIdentifier;
+import org.onap.policy.apex.model.basicmodel.service.ModelService;
+import org.onap.policy.common.parameters.ParameterService;
 
 /**
  * Test the ApexMain class.
@@ -114,13 +115,13 @@ public class ApexMainTest {
         OutputStream outContent = new ByteArrayOutputStream();
         System.setOut(new PrintStream(outContent));
 
-        String[] args = { "-p", "src/test/resources/parameters/correctParams.json" };
+        String[] args = {"-p", "src/test/resources/parameters/correctParams.json"};
 
         final ApexMain apexMain = new ApexMain(args);
-        assertEquals("MyApexEngine",
-            apexMain.getApexParametersMap().values().iterator().next().getEngineServiceParameters().getName());
-        await().atMost(200, TimeUnit.MILLISECONDS).until(() -> outContent.toString()
-                .contains("Added the action listener to the engine"));
+        assertEquals("MyApexEngine", apexMain.getApexParameters().getEngineServiceParameters().getName());
+        await().atMost(200, TimeUnit.MILLISECONDS)
+            .until(() -> outContent.toString().contains("Added the action listener to the engine"));
+        assertTrue(apexMain.isAlive());
         apexMain.shutdown();
     }
 
@@ -129,16 +130,15 @@ public class ApexMainTest {
         OutputStream outContent = new ByteArrayOutputStream();
         System.setOut(new PrintStream(outContent));
 
-        String[] args = { "-p", "src/test/resources/parameters/correctParamsJavaProperties.json" };
+        String[] args = {"-p", "src/test/resources/parameters/correctParamsJavaProperties.json"};
 
         final ApexMain apexMain = new ApexMain(args);
-        assertEquals("MyApexEngine",
-            apexMain.getApexParametersMap().values().iterator().next().getEngineServiceParameters().getName());
+        assertEquals("MyApexEngine", apexMain.getApexParameters().getEngineServiceParameters().getName());
 
         assertEquals("trust-store-file", System.getProperty("javax.net.ssl.trustStore"));
         assertEquals("Pol1cy_0nap", System.getProperty("javax.net.ssl.trustStorePassword"));
-        await().atMost(10000, TimeUnit.MILLISECONDS).until(() -> outContent.toString()
-                .contains("Added the action listener to the engine"));
+        await().atMost(10000, TimeUnit.MILLISECONDS)
+            .until(() -> outContent.toString().contains("Added the action listener to the engine"));
         apexMain.shutdown();
     }
 
@@ -146,46 +146,41 @@ public class ApexMainTest {
     public void testCorrectParametersWithMultiplePolicies() throws ApexException {
         OutputStream outContent = new ByteArrayOutputStream();
         System.setOut(new PrintStream(outContent));
-        Map<ToscaConceptIdentifier, String[]> argsMap = new HashMap<ToscaConceptIdentifier, String[]>();
-        String[] args = {"-p", "src/test/resources/parameters/correctParams.json"};
-        argsMap.put(new ToscaConceptIdentifier("id1", "v1"), args);
-        final ApexMain apexMain = new ApexMain(argsMap);
-        ApexParameters apexParam = (ApexParameters) apexMain.getApexParametersMap().values().toArray()[0];
-        assertEquals("MyApexEngine", apexParam.getEngineServiceParameters().getName());
-        apexMain.shutdown();
+        String[] args1 = {"-p", "src/test/resources/parameters/correctParams.json"};
+        String[] args2 = {"-p", "src/test/resources/parameters/correctParams2.json"};
+        final ApexMain apexMain1 = new ApexMain(args1);
+        final ApexMain apexMain2 = new ApexMain(args2);
+        assertEquals("MyApexEngine", apexMain1.getApexParameters().getEngineServiceParameters().getName());
+        assertEquals("MyApexEngine2", apexMain2.getApexParameters().getEngineServiceParameters().getName());
         final String outString = outContent.toString();
-        assertThat(outString).contains("Added the action listener to the engine");
+        assertThat(outString).contains("Added the action listener to the engine")
+            .contains("Created apex engine MyApexEngine").contains("Created apex engine MyApexEngine2");
+        assertTrue(apexMain1.isAlive());
+        assertTrue(apexMain2.isAlive());
+        apexMain1.shutdown();
+        apexMain2.shutdown();
+        ModelService.clear();
+        ParameterService.clear();
     }
 
     @Test
     public void testInCorrectParametersWithMultiplePolicies() throws ApexException {
-        OutputStream outContent = new ByteArrayOutputStream();
-        System.setOut(new PrintStream(outContent));
-        Map<ToscaConceptIdentifier, String[]> argsMap = new HashMap<ToscaConceptIdentifier, String[]>();
         String[] args = {"-p", "src/test/resources/parameters/correctParams.json"};
-        argsMap.put(new ToscaConceptIdentifier("id1", "v1"), args);
-        argsMap.put(new ToscaConceptIdentifier("id2", "v2"), args);
-        final ApexMain apexMain = new ApexMain(argsMap);
-        ApexParameters apexParam = (ApexParameters) apexMain.getApexParametersMap().values().toArray()[0];
-        assertEquals("MyApexEngine", apexParam.getEngineServiceParameters().getName());
-        apexMain.shutdown();
-        final String outString = outContent.toString();
-        assertThat(outString).contains("I/O Parameters [TheFileConsumer1]/[FirstProducer] for id2:v2 are duplicates. "
-            + "So this policy is not executed");
-        assertEquals(1, apexMain.getApexParametersMap().size()); // only id1:v1 is kept in the map, id2:v2 failed
+        final ApexMain apexMain1 = new ApexMain(args);
+        assertThatThrownBy(() -> new ApexMain(args)).hasMessage("start of Apex service failed because this"
+            + " policy has the following duplicate I/O parameters: [TheFileConsumer1]/[FirstProducer]");
+        apexMain1.shutdown();
     }
 
     @Test
     public void testInvalidArgsWithMultiplePolicies() throws ApexException {
         OutputStream outContent = new ByteArrayOutputStream();
         System.setOut(new PrintStream(outContent));
-        Map<ToscaConceptIdentifier, String[]> argsMap = new HashMap<ToscaConceptIdentifier, String[]>();
         String[] args = {"-c", "file1", "-m", "file2"};
-        argsMap.put(new ToscaConceptIdentifier("id1", "v1"), args);
-        final ApexMain apexMain = new ApexMain(argsMap);
+        final ApexMain apexMain = new ApexMain(args);
         final String outString = outContent.toString();
         apexMain.shutdown();
         assertThat(outString).contains("Arguments validation failed", "start of Apex service failed");
-        assertThat(apexMain.getApexParametersMap()).isEmpty(); // No policy is running in the engine
+        assertFalse(apexMain.isAlive()); // No policy is running in the engine
     }
 }
diff --git a/services/services-engine/src/test/resources/parameters/correctParams.json b/services/services-engine/src/test/resources/parameters/correctParams.json
index 43fef1cbe..7ea06d715 100644
--- a/services/services-engine/src/test/resources/parameters/correctParams.json
+++ b/services/services-engine/src/test/resources/parameters/correctParams.json
@@ -501,7 +501,8 @@
                 },
                 "eventProtocolParameters": {
                   "eventProtocol": "JSON"
-                }
+                },
+                "eventName": "BasicEvent"
               }
             }
           }
diff --git a/services/services-engine/src/test/resources/parameters/correctParams2.json b/services/services-engine/src/test/resources/parameters/correctParams2.json
new file mode 100644
index 000000000..2d2ebff23
--- /dev/null
+++ b/services/services-engine/src/test/resources/parameters/correctParams2.json
@@ -0,0 +1,513 @@
+{
+  "tosca_definitions_version": "tosca_simple_yaml_1_1_0",
+  "topology_template": {
+    "policies": [
+      {
+        "onap.policies.apex.Simplecontrolloop": {
+          "type": "onap.policies.native.Apex",
+          "type_version": "1.0.0",
+          "name": "onap.policies.apex.Simplecontrolloop",
+          "version": "1.0.0",
+          "properties": {
+            "engineServiceParameters": {
+              "name": "MyApexEngine2",
+              "version": "0.0.1",
+              "id": 45,
+              "instanceCount": 2,
+              "deploymentPort": 65522,
+              "policy_type_impl": {
+                "apexPolicyModel": {
+                  "key": {
+                    "name": "SmallModel",
+                    "version": "0.0.1"
+                  },
+                  "keyInformation": {
+                    "key": {
+                      "name": "SmallModel_KeyInfo",
+                      "version": "0.0.1"
+                    },
+                    "keyInfoMap": {
+                      "entry": [
+                        {
+                          "key": {
+                            "name": "BasicContextAlbum",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "BasicContextAlbum",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "fec1b353-b35f-4384-b7d9-69622059c248",
+                            "description": "Generated description for a concept called \"BasicContextAlbum\" with version \"0.0.1\" and UUID \"fec1b353-b35f-4384-b7d9-69622059c248\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "BasicEvent",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "BasicEvent",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "cc8d3c1a-e975-459a-bcd2-69f423eaa1f3",
+                            "description": "Generated description for a concept called \"BasicEvent\" with version \"0.0.1\" and UUID \"cc8d3c1a-e975-459a-bcd2-69f423eaa1f3\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "BasicPolicy",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "BasicPolicy",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "d0c5d8ee-5fe7-4978-89ce-4a3e69cad043",
+                            "description": "Generated description for a concept called \"BasicPolicy\" with version \"0.0.1\" and UUID \"d0c5d8ee-5fe7-4978-89ce-4a3e69cad043\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "BasicTask",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "BasicTask",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "c5651414-fc1c-493b-878d-75f0ce685c36",
+                            "description": "Generated description for a concept called \"BasicTask\" with version \"0.0.1\" and UUID \"c5651414-fc1c-493b-878d-75f0ce685c36\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "IntType",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "IntType",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "790ff718-8dc0-44e0-89d8-1b3bbe238310",
+                            "description": "Generated description for a concept called \"IntType\" with version \"0.0.1\" and UUID \"790ff718-8dc0-44e0-89d8-1b3bbe238310\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "SmallModel",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "SmallModel",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "a1bd1f4e-713b-456b-b1a8-bb48beee28e8",
+                            "description": "Generated description for a concept called \"SmallModel\" with version \"0.0.1\" and UUID \"a1bd1f4e-713b-456b-b1a8-bb48beee28e8\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "SmallModel_Albums",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "SmallModel_Albums",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "72bed9af-ab7d-3379-b9f7-b5eca5c9ef22",
+                            "description": "Generated description for concept referred to by key \"SmallModel_Albums:0.0.1\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "SmallModel_Events",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "SmallModel_Events",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "796dc6b0-627d-34ae-a5e2-1bc4b4b486b8",
+                            "description": "Generated description for concept referred to by key \"SmallModel_Events:0.0.1\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "SmallModel_KeyInfo",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "SmallModel_KeyInfo",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "b4876774-6907-3d27-a2b8-f05737c5ee4a",
+                            "description": "Generated description for concept referred to by key \"SmallModel_KeyInfo:0.0.1\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "SmallModel_Policies",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "SmallModel_Policies",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "5bcf946b-67be-3190-a906-f954896f999f",
+                            "description": "Generated description for concept referred to by key \"SmallModel_Policies:0.0.1\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "SmallModel_Schemas",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "SmallModel_Schemas",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "c25bf5c3-7f1e-3667-b8a9-971ba21517bc",
+                            "description": "Generated description for concept referred to by key \"SmallModel_Schemas:0.0.1\""
+                          }
+                        },
+                        {
+                          "key": {
+                            "name": "SmallModel_Tasks",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "SmallModel_Tasks",
+                              "version": "0.0.1"
+                            },
+                            "UUID": "43b015ca-2ed1-3a35-b103-e8a5aa68f1ef",
+                            "description": "Generated description for concept referred to by key \"SmallModel_Tasks:0.0.1\""
+                          }
+                        }
+                      ]
+                    }
+                  },
+                  "policies": {
+                    "key": {
+                      "name": "SmallModel_Policies",
+                      "version": "0.0.1"
+                    },
+                    "policyMap": {
+                      "entry": [
+                        {
+                          "key": {
+                            "name": "BasicPolicy",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "policyKey": {
+                              "name": "BasicPolicy",
+                              "version": "0.0.1"
+                            },
+                            "template": "FREEFORM",
+                            "state": {
+                              "entry": [
+                                {
+                                  "key": "OnlyState",
+                                  "value": {
+                                    "stateKey": {
+                                      "parentKeyName": "BasicPolicy",
+                                      "parentKeyVersion": "0.0.1",
+                                      "parentLocalName": "NULL",
+                                      "localName": "OnlyState"
+                                    },
+                                    "trigger": {
+                                      "name": "BasicEvent",
+                                      "version": "0.0.1"
+                                    },
+                                    "stateOutputs": {
+                                      "entry": [
+                                        {
+                                          "key": "OnlyOutput",
+                                          "value": {
+                                            "key": {
+                                              "parentKeyName": "BasicPolicy",
+                                              "parentKeyVersion": "0.0.1",
+                                              "parentLocalName": "OnlyState",
+                                              "localName": "OnlyOutput"
+                                            },
+                                            "outgoingEvent": {
+                                              "name": "BasicEvent",
+                                              "version": "0.0.1"
+                                            },
+                                            "nextState": {
+                                              "parentKeyName": "NULL",
+                                              "parentKeyVersion": "0.0.0",
+                                              "parentLocalName": "NULL",
+                                              "localName": "NULL"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    },
+                                    "contextAlbumReference": [
+                                      {
+                                        "name": "BasicContextAlbum",
+                                        "version": "0.0.1"
+                                      }
+                                    ],
+                                    "taskSelectionLogic": {
+                                      "key": "NULL",
+                                      "logicFlavour": "UNDEFINED",
+                                      "logic": ""
+                                    },
+                                    "stateFinalizerLogicMap": {
+                                      "entry": []
+                                    },
+                                    "defaultTask": {
+                                      "name": "BasicTask",
+                                      "version": "0.0.1"
+                                    },
+                                    "taskReferences": {
+                                      "entry": [
+                                        {
+                                          "key": {
+                                            "name": "BasicTask",
+                                            "version": "0.0.1"
+                                          },
+                                          "value": {
+                                            "key": {
+                                              "parentKeyName": "BasicPolicy",
+                                              "parentKeyVersion": "0.0.1",
+                                              "parentLocalName": "OnlyState",
+                                              "localName": "BasicTask"
+                                            },
+                                            "outputType": "DIRECT",
+                                            "output": {
+                                              "parentKeyName": "BasicPolicy",
+                                              "parentKeyVersion": "0.0.1",
+                                              "parentLocalName": "OnlyState",
+                                              "localName": "OnlyOutput"
+                                            }
+                                          }
+                                        }
+                                      ]
+                                    }
+                                  }
+                                }
+                              ]
+                            },
+                            "firstState": "OnlyState"
+                          }
+                        }
+                      ]
+                    }
+                  },
+                  "tasks": {
+                    "key": {
+                      "name": "SmallModel_Tasks",
+                      "version": "0.0.1"
+                    },
+                    "taskMap": {
+                      "entry": [
+                        {
+                          "key": {
+                            "name": "BasicTask",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "BasicTask",
+                              "version": "0.0.1"
+                            },
+                            "inputFields": {
+                              "entry": [
+                                {
+                                  "key": "intPar",
+                                  "value": {
+                                    "key": "intPar",
+                                    "fieldSchemaKey": {
+                                      "name": "IntType",
+                                      "version": "0.0.1"
+                                    },
+                                    "optional": false
+                                  }
+                                }
+                              ]
+                            },
+                            "outputFields": {
+                              "entry": [
+                                {
+                                  "key": "intPar",
+                                  "value": {
+                                    "key": "intPar",
+                                    "fieldSchemaKey": {
+                                      "name": "IntType",
+                                      "version": "0.0.1"
+                                    },
+                                    "optional": false
+                                  }
+                                }
+                              ]
+                            },
+                            "taskParameters": {
+                              "entry": []
+                            },
+                            "contextAlbumReference": [
+                              {
+                                "name": "BasicContextAlbum",
+                                "version": "0.0.1"
+                              }
+                            ],
+                            "taskLogic": {
+                              "key": "TaskLogic",
+                              "logicFlavour": "JAVASCRIPT",
+                              "logic": "executor.logger.debug(executor.subject.id);\nvar gc = executor.getContextAlbum(\"BasicContextAlbum\");\nexecutor.logger.debug(gc.name);\nexecutor.logger.debug(executor.inFields);\n\nexecutor.logger.debug(executor.eo);\n\nvar returnValue = executor.isTrue;"
+                            }
+                          }
+                        }
+                      ]
+                    }
+                  },
+                  "events": {
+                    "key": {
+                      "name": "SmallModel_Events",
+                      "version": "0.0.1"
+                    },
+                    "eventMap": {
+                      "entry": [
+                        {
+                          "key": {
+                            "name": "BasicEvent",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "BasicEvent",
+                              "version": "0.0.1"
+                            },
+                            "nameSpace": "org.onap.policy.apex.events",
+                            "source": "source",
+                            "target": "target",
+                            "parameter": {
+                              "entry": [
+                                {
+                                  "key": "intPar",
+                                  "value": {
+                                    "key": "intPar",
+                                    "fieldSchemaKey": {
+                                      "name": "IntType",
+                                      "version": "0.0.1"
+                                    },
+                                    "optional": false
+                                  }
+                                }
+                              ]
+                            }
+                          }
+                        }
+                      ]
+                    }
+                  },
+                  "albums": {
+                    "key": {
+                      "name": "SmallModel_Albums",
+                      "version": "0.0.1"
+                    },
+                    "albums": {
+                      "entry": [
+                        {
+                          "key": {
+                            "name": "BasicContextAlbum",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "BasicContextAlbum",
+                              "version": "0.0.1"
+                            },
+                            "scope": "GLOBAL",
+                            "isWritable": true,
+                            "itemSchema": {
+                              "name": "IntType",
+                              "version": "0.0.1"
+                            }
+                          }
+                        }
+                      ]
+                    }
+                  },
+                  "schemas": {
+                    "key": {
+                      "name": "SmallModel_Schemas",
+                      "version": "0.0.1"
+                    },
+                    "schemas": {
+                      "entry": [
+                        {
+                          "key": {
+                            "name": "IntType",
+                            "version": "0.0.1"
+                          },
+                          "value": {
+                            "key": {
+                              "name": "IntType",
+                              "version": "0.0.1"
+                            },
+                            "schemaFlavour": "Java",
+                            "schemaDefinition": "java.lang.Integer"
+                          }
+                        }
+                      ]
+                    }
+                  }
+                }
+              },
+              "engineParameters": {
+                "executorParameters": {
+                  "JAVASCRIPT": {
+                    "parameterClassName": "org.onap.policy.apex.service.engine.parameters.dummyclasses.SuperDooperExecutorParameters"
+                  }
+                }
+              }
+            },
+            "eventOutputParameters": {
+              "FirstProducer2": {
+                "carrierTechnologyParameters": {
+                  "carrierTechnology": "FILE",
+                  "parameters": {
+                    "standardIo": true
+                  }
+                },
+                "eventProtocolParameters": {
+                  "eventProtocol": "JSON"
+                }
+              }
+            },
+            "eventInputParameters": {
+              "TheFileConsumer2": {
+                "carrierTechnologyParameters": {
+                  "carrierTechnology": "FILE",
+                  "parameters": {
+                    "fileName": "src/test/resources/events/TestPojoEvent.json"
+                  }
+                },
+                "eventProtocolParameters": {
+                  "eventProtocol": "JSON"
+                },
+                "eventName": "BasicEvent"
+              }
+            }
+          }
+        }
+      }
+    ]
+  }
+}
\ No newline at end of file
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 4d560a3bb..03e97215b 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
@@ -1,7 +1,7 @@
 /*-
  * ============LICENSE_START=======================================================
  *  Copyright (C) 2019-2021 Nordix Foundation.
- *  Modifications Copyright (C) 2020 Bell Canada. All rights reserved.
+ *  Modifications Copyright (C) 2020-2021 Bell Canada. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,13 +24,36 @@ package org.onap.policy.apex.services.onappf.handler;
 import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+import org.onap.policy.apex.core.engine.EngineParameters;
+import org.onap.policy.apex.core.engine.TaskParameters;
 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.concepts.AxKeyInfo;
+import org.onap.policy.apex.model.basicmodel.concepts.AxKeyInformation;
+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.contextmodel.concepts.AxContextSchema;
+import org.onap.policy.apex.model.contextmodel.concepts.AxContextSchemas;
 import org.onap.policy.apex.model.enginemodel.concepts.AxEngineModel;
+import org.onap.policy.apex.model.eventmodel.concepts.AxEvent;
+import org.onap.policy.apex.model.eventmodel.concepts.AxEvents;
+import org.onap.policy.apex.model.policymodel.concepts.AxPolicies;
+import org.onap.policy.apex.model.policymodel.concepts.AxPolicy;
+import org.onap.policy.apex.model.policymodel.concepts.AxPolicyModel;
+import org.onap.policy.apex.model.policymodel.concepts.AxTask;
+import org.onap.policy.apex.model.policymodel.concepts.AxTasks;
 import org.onap.policy.apex.service.engine.main.ApexMain;
+import org.onap.policy.apex.service.parameters.ApexParameterConstants;
+import org.onap.policy.apex.service.parameters.ApexParameters;
 import org.onap.policy.apex.services.onappf.exception.ApexStarterException;
+import org.onap.policy.common.parameters.ParameterService;
 import org.onap.policy.common.utils.coder.CoderException;
 import org.onap.policy.common.utils.coder.StandardCoder;
 import org.onap.policy.models.tosca.authorative.concepts.ToscaConceptIdentifier;
@@ -49,7 +72,7 @@ public class ApexEngineHandler {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(ApexEngineHandler.class);
 
-    private ApexMain apexMain;
+    private Map<ToscaConceptIdentifier, ApexMain> apexMainMap;
 
     /**
      * Constructs the object. Extracts the config and model files from each policy and instantiates the apex engine.
@@ -57,13 +80,13 @@ public class ApexEngineHandler {
      * @param policies the list of policies
      * @throws ApexStarterException if the apex engine instantiation failed using the policies passed
      */
-    public ApexEngineHandler(List<ToscaPolicy> policies)  throws ApexStarterException {
-        Map<ToscaConceptIdentifier, String[]> policyArgsMap = createPolicyArgsMap(policies);
+    public ApexEngineHandler(List<ToscaPolicy> policies) throws ApexStarterException {
         LOGGER.debug("Starting apex engine.");
-        try {
-            apexMain = new ApexMain(policyArgsMap);
-        } catch (ApexException e) {
-            throw new ApexStarterException(e);
+        apexMainMap = initiateApexEngineForPolicies(policies);
+        if (apexMainMap.isEmpty()) {
+            ModelService.clear();
+            ParameterService.clear();
+            throw new ApexStarterException("Apex Engine failed to start.");
         }
     }
 
@@ -74,20 +97,136 @@ public class ApexEngineHandler {
      * @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.");
+        List<ToscaConceptIdentifier> runningPolicies = getRunningPolicies();
+        List<ToscaPolicy> policiesToDeploy = policies.stream()
+            .filter(policy -> !runningPolicies.contains(policy.getIdentifier())).collect(Collectors.toList());
+        List<ToscaConceptIdentifier> policiesToUnDeploy = runningPolicies.stream()
+            .filter(polId -> policies.stream().noneMatch(policy -> policy.getIdentifier().equals(polId)))
+            .collect(Collectors.toList());
+        Map<ToscaConceptIdentifier, ApexMain> undeployedPoliciesMainMap = new LinkedHashMap<>();
+        policiesToUnDeploy.forEach(policyId -> {
+            ApexMain apexMain = apexMainMap.get(policyId);
+            try {
+                apexMain.shutdown();
+                undeployedPoliciesMainMap.put(policyId, apexMain);
+                apexMainMap.remove(policyId);
+            } catch (ApexException e) {
+                LOGGER.error("Shutting down policy {} failed", policyId, e);
+            }
+        });
+        if (!undeployedPoliciesMainMap.isEmpty()) {
+            updateModelAndParameterServices(undeployedPoliciesMainMap);
         }
-        Map<ToscaConceptIdentifier, String[]> policyArgsMap = createPolicyArgsMap(policies);
-        try {
-            apexMain.updateModel(policyArgsMap);
-        } catch (ApexException e) {
-            throw new ApexStarterException(e);
+        if (!policiesToDeploy.isEmpty()) {
+            Map<ToscaConceptIdentifier, ApexMain> mainMap = initiateApexEngineForPolicies(policiesToDeploy);
+            if (mainMap.isEmpty()) {
+                throw new ApexStarterException("Updating the APEX engine with new policies failed.");
+            }
+            apexMainMap.putAll(mainMap);
+        }
+        if (apexMainMap.isEmpty()) {
+            ModelService.clear();
+            ParameterService.clear();
+        }
+    }
+
+    /**
+     * Clear the corresponding items from ModelService and ParameterService.
+     *
+     * @param undeployedPoliciesMainMap the policies that are undeployed
+     */
+    private void updateModelAndParameterServices(Map<ToscaConceptIdentifier, ApexMain> undeployedPoliciesMainMap) {
+        Set<String> inputParamKeysToRetain = new HashSet<>();
+        Set<String> outputParamKeysToRetain = new HashSet<>();
+        List<TaskParameters> taskParametersToRetain = new ArrayList<>();
+        List<String> executorParamKeysToRetain = new ArrayList<>();
+        List<String> schemaParamKeysToRetain = new ArrayList<>();
+
+        List<AxArtifactKey> keyInfoKeystoRetain = new ArrayList<>();
+        List<AxArtifactKey> schemaKeystoRetain = new ArrayList<>();
+        List<AxArtifactKey> eventKeystoRetain = new ArrayList<>();
+        List<AxArtifactKey> albumKeystoRetain = new ArrayList<>();
+        List<AxArtifactKey> taskKeystoRetain = new ArrayList<>();
+        List<AxArtifactKey> policyKeystoRetain = new ArrayList<>();
+
+        apexMainMap.values().forEach(main -> {
+            inputParamKeysToRetain.addAll(main.getApexParameters().getEventInputParameters().keySet());
+            outputParamKeysToRetain.addAll(main.getApexParameters().getEventOutputParameters().keySet());
+            taskParametersToRetain.addAll(
+                main.getApexParameters().getEngineServiceParameters().getEngineParameters().getTaskParameters());
+            executorParamKeysToRetain.addAll(main.getApexParameters().getEngineServiceParameters().getEngineParameters()
+                .getExecutorParameterMap().keySet());
+            schemaParamKeysToRetain.addAll(main.getApexParameters().getEngineServiceParameters().getEngineParameters()
+                .getContextParameters().getSchemaParameters().getSchemaHelperParameterMap().keySet());
+
+            keyInfoKeystoRetain
+                .addAll(main.getActivator().getPolicyModel().getKeyInformation().getKeyInfoMap().keySet());
+            schemaKeystoRetain.addAll(main.getActivator().getPolicyModel().getSchemas().getSchemasMap().keySet());
+            eventKeystoRetain.addAll(main.getActivator().getPolicyModel().getEvents().getEventMap().keySet());
+            albumKeystoRetain.addAll(main.getActivator().getPolicyModel().getAlbums().getAlbumsMap().keySet());
+            taskKeystoRetain.addAll(main.getActivator().getPolicyModel().getTasks().getTaskMap().keySet());
+            policyKeystoRetain.addAll(main.getActivator().getPolicyModel().getPolicies().getPolicyMap().keySet());
+        });
+        for (ApexMain main : undeployedPoliciesMainMap.values()) {
+            ApexParameters existingParameters = ParameterService.get(ApexParameterConstants.MAIN_GROUP_NAME);
+            List<String> eventInputParamKeysToRemove = main.getApexParameters().getEventInputParameters().keySet()
+                .stream().filter(key -> !inputParamKeysToRetain.contains(key)).collect(Collectors.toList());
+            List<String> eventOutputParamKeysToRemove = main.getApexParameters().getEventOutputParameters().keySet()
+                .stream().filter(key -> !outputParamKeysToRetain.contains(key)).collect(Collectors.toList());
+            eventInputParamKeysToRemove.forEach(existingParameters.getEventInputParameters()::remove);
+            eventOutputParamKeysToRemove.forEach(existingParameters.getEventOutputParameters()::remove);
+            EngineParameters engineParameters =
+                main.getApexParameters().getEngineServiceParameters().getEngineParameters();
+            final List<TaskParameters> taskParametersToRemove = engineParameters.getTaskParameters().stream()
+                .filter(taskParameter -> !taskParametersToRetain.contains(taskParameter)).collect(Collectors.toList());
+            final List<String> executorParamKeysToRemove = engineParameters.getExecutorParameterMap().keySet().stream()
+                .filter(key -> !executorParamKeysToRetain.contains(key)).collect(Collectors.toList());
+            final List<String> schemaParamKeysToRemove =
+                engineParameters.getContextParameters().getSchemaParameters().getSchemaHelperParameterMap().keySet()
+                    .stream().filter(key -> !schemaParamKeysToRetain.contains(key)).collect(Collectors.toList());
+            EngineParameters aggregatedEngineParameters =
+                existingParameters.getEngineServiceParameters().getEngineParameters();
+            aggregatedEngineParameters.getTaskParameters().removeAll(taskParametersToRemove);
+            executorParamKeysToRemove.forEach(aggregatedEngineParameters.getExecutorParameterMap()::remove);
+            schemaParamKeysToRemove.forEach(aggregatedEngineParameters.getContextParameters().getSchemaParameters()
+                .getSchemaHelperParameterMap()::remove);
+
+            final AxPolicyModel policyModel = main.getActivator().getPolicyModel();
+            final List<AxArtifactKey> keyInfoKeystoRemove = policyModel.getKeyInformation().getKeyInfoMap().keySet()
+                .stream().filter(key -> !keyInfoKeystoRetain.contains(key)).collect(Collectors.toList());
+            final List<AxArtifactKey> schemaKeystoRemove = policyModel.getSchemas().getSchemasMap().keySet().stream()
+                .filter(key -> !schemaKeystoRetain.contains(key)).collect(Collectors.toList());
+            final List<AxArtifactKey> eventKeystoRemove = policyModel.getEvents().getEventMap().keySet().stream()
+                .filter(key -> !eventKeystoRetain.contains(key)).collect(Collectors.toList());
+            final List<AxArtifactKey> albumKeystoRemove = policyModel.getAlbums().getAlbumsMap().keySet().stream()
+                .filter(key -> !albumKeystoRetain.contains(key)).collect(Collectors.toList());
+            final List<AxArtifactKey> taskKeystoRemove = policyModel.getTasks().getTaskMap().keySet().stream()
+                .filter(key -> !taskKeystoRetain.contains(key)).collect(Collectors.toList());
+            final List<AxArtifactKey> policyKeystoRemove = policyModel.getPolicies().getPolicyMap().keySet().stream()
+                .filter(key -> !policyKeystoRetain.contains(key)).collect(Collectors.toList());
+
+            final Map<AxArtifactKey, AxKeyInfo> keyInfoMap =
+                ModelService.getModel(AxKeyInformation.class).getKeyInfoMap();
+            final Map<AxArtifactKey, AxContextSchema> schemasMap =
+                ModelService.getModel(AxContextSchemas.class).getSchemasMap();
+            final Map<AxArtifactKey, AxEvent> eventMap = ModelService.getModel(AxEvents.class).getEventMap();
+            final Map<AxArtifactKey, AxContextAlbum> albumsMap =
+                ModelService.getModel(AxContextAlbums.class).getAlbumsMap();
+            final Map<AxArtifactKey, AxTask> taskMap = ModelService.getModel(AxTasks.class).getTaskMap();
+            final Map<AxArtifactKey, AxPolicy> policyMap = ModelService.getModel(AxPolicies.class).getPolicyMap();
+
+            keyInfoKeystoRemove.forEach(keyInfoMap::remove);
+            schemaKeystoRemove.forEach(schemasMap::remove);
+            eventKeystoRemove.forEach(eventMap::remove);
+            albumKeystoRemove.forEach(albumsMap::remove);
+            taskKeystoRemove.forEach(taskMap::remove);
+            policyKeystoRemove.forEach(policyMap::remove);
         }
     }
 
-    private Map<ToscaConceptIdentifier, String[]> createPolicyArgsMap(List<ToscaPolicy> policies)
+    private Map<ToscaConceptIdentifier, ApexMain> initiateApexEngineForPolicies(List<ToscaPolicy> policies)
         throws ApexStarterException {
-        Map<ToscaConceptIdentifier, String[]> policyArgsMap = new LinkedHashMap<>();
+        Map<ToscaConceptIdentifier, ApexMain> mainMap = new LinkedHashMap<>();
         for (ToscaPolicy policy : policies) {
             String policyName = policy.getIdentifier().getName();
             final StandardCoder standardCoder = new StandardCoder();
@@ -103,34 +242,38 @@ public class ApexEngineHandler {
                 throw new ApexStarterException(e);
             }
             final String[] apexArgs = {"-p", file.getAbsolutePath()};
-            policyArgsMap.put(policy.getIdentifier(), apexArgs);
+            LOGGER.info("Starting apex engine for policy {}", policy.getIdentifier());
+            try {
+                ApexMain apexMain = new ApexMain(apexArgs);
+                mainMap.put(policy.getIdentifier(), apexMain);
+            } catch (Exception e) {
+                LOGGER.error("Execution of policy {} failed", policy.getIdentifier(), e);
+            }
         }
-        return policyArgsMap;
+        return mainMap;
     }
 
     /**
      * Method to get the APEX engine statistics.
      */
     public List<AxEngineModel> getEngineStats() {
-        List<AxEngineModel> engineStats = null;
-        if (null != apexMain && apexMain.isAlive()) {
-            engineStats = apexMain.getEngineStats();
-        }
-        return engineStats;
+        // engineStats from all the apexMain instances running individual tosca policies are combined here.
+        return apexMainMap.values().stream().filter(apexMain -> (null != apexMain && apexMain.isAlive()))
+            .flatMap(m -> m.getEngineStats().stream()).collect(Collectors.toList());
     }
 
     /**
      * Method to check whether the apex engine is running or not.
      */
     public boolean isApexEngineRunning() {
-        return null != apexMain && apexMain.isAlive();
+        return apexMainMap.values().stream().anyMatch(apexMain -> (null != apexMain && apexMain.isAlive()));
     }
 
     /**
      * Method that return the list of running policies in the apex engine.
      */
     public List<ToscaConceptIdentifier> getRunningPolicies() {
-        return new ArrayList<>(apexMain.getApexParametersMap().keySet());
+        return new ArrayList<>(apexMainMap.keySet());
     }
 
     /**
@@ -139,8 +282,12 @@ public class ApexEngineHandler {
     public void shutdown() throws ApexStarterException {
         try {
             LOGGER.debug("Shutting down apex engine.");
-            apexMain.shutdown();
-            apexMain = null;
+            for (ApexMain apexMain : apexMainMap.values()) {
+                apexMain.shutdown();
+            }
+            apexMainMap.clear();
+            ModelService.clear();
+            ParameterService.clear();
         } catch (final ApexException e) {
             throw new ApexStarterException(e);
         }