diff --git a/java/operator/org.eclipse.theia.cloud.operator/src/main/java/org/eclipse/theia/cloud/operator/handler/appdef/EagerStartAppDefinitionAddedHandler.java b/java/operator/org.eclipse.theia.cloud.operator/src/main/java/org/eclipse/theia/cloud/operator/handler/appdef/EagerStartAppDefinitionAddedHandler.java
index 97db8166..d92d779d 100644
--- a/java/operator/org.eclipse.theia.cloud.operator/src/main/java/org/eclipse/theia/cloud/operator/handler/appdef/EagerStartAppDefinitionAddedHandler.java
+++ b/java/operator/org.eclipse.theia.cloud.operator/src/main/java/org/eclipse/theia/cloud/operator/handler/appdef/EagerStartAppDefinitionAddedHandler.java
@@ -163,6 +163,86 @@ public boolean appDefinitionAdded(AppDefinition appDefinition, String correlatio
         return true;
     }
 
+    @Override
+    public boolean appDefinitionModified(AppDefinition appDefinition, String correlationId) {
+        AppDefinitionSpec spec = appDefinition.getSpec();
+        LOGGER.info(formatLogMessage(correlationId, "Handling " + spec));
+
+        String appDefinitionResourceName = appDefinition.getMetadata().getName();
+        String appDefinitionResourceUID = appDefinition.getMetadata().getUid();
+        int instances = spec.getMinInstances();
+
+        /* Create ingress if not existing */
+        if (!TheiaCloudIngressUtil.checkForExistingIngressAndAddOwnerReferencesIfMissing(client.kubernetes(),
+                client.namespace(), appDefinition, correlationId)) {
+            LOGGER.error(formatLogMessage(correlationId,
+                    "Expected ingress '" + spec.getIngressname() + "' for app definition '" + appDefinitionResourceName
+                            + "' does not exist. Abort handling app definition."));
+            return false;
+        } else {
+            LOGGER.trace(formatLogMessage(correlationId, "Ingress available already"));
+        }
+
+        /* Get existing services for this app definition */
+        List<Service> existingServices = K8sUtil.getExistingServices(client.kubernetes(), client.namespace(),
+                appDefinitionResourceName, appDefinitionResourceUID);
+
+        /* Compute missing services */
+        Set<Integer> missingServiceIds = TheiaCloudServiceUtil.computeIdsOfMissingServices(appDefinition, correlationId,
+                instances, existingServices);
+
+        Map<String, String> labelsToAdd = new HashMap<String, String>();
+
+        /* Create missing services for this app definition */
+        for (int instance : missingServiceIds) {
+            createAndApplyService(client.kubernetes(), client.namespace(), correlationId, appDefinitionResourceName,
+                    appDefinitionResourceUID, instance, appDefinition, arguments.isUseKeycloak(), labelsToAdd);
+        }
+
+        if (arguments.isUseKeycloak()) {
+            /* Get existing configmaps for this app definition */
+            List<ConfigMap> existingConfigMaps = K8sUtil.getExistingConfigMaps(client.kubernetes(), client.namespace(),
+                    appDefinitionResourceName, appDefinitionResourceUID);
+            List<ConfigMap> existingProxyConfigMaps = existingConfigMaps.stream()//
+                    .filter(configmap -> LABEL_VALUE_PROXY.equals(configmap.getMetadata().getLabels().get(LABEL_KEY)))//
+                    .collect(Collectors.toList());
+            List<ConfigMap> existingEmailsConfigMaps = existingConfigMaps.stream()//
+                    .filter(configmap -> LABEL_VALUE_EMAILS.equals(configmap.getMetadata().getLabels().get(LABEL_KEY)))//
+                    .collect(Collectors.toList());
+
+            /* Compute missing configmaps */
+            Set<Integer> missingProxyIds = TheiaCloudConfigMapUtil.computeIdsOfMissingProxyConfigMaps(appDefinition,
+                    correlationId, instances, existingProxyConfigMaps);
+            Set<Integer> missingEmailIds = TheiaCloudConfigMapUtil.computeIdsOfMissingEmailConfigMaps(appDefinition,
+                    correlationId, instances, existingEmailsConfigMaps);
+
+            /* Create missing configmaps for this app definition */
+            for (int instance : missingProxyIds) {
+                createAndApplyProxyConfigMap(client.kubernetes(), client.namespace(), correlationId,
+                        appDefinitionResourceName, appDefinitionResourceUID, instance, appDefinition, labelsToAdd);
+            }
+            for (int instance : missingEmailIds) {
+                createAndApplyEmailConfigMap(client.kubernetes(), client.namespace(), correlationId,
+                        appDefinitionResourceName, appDefinitionResourceUID, instance, appDefinition, labelsToAdd);
+            }
+        }
+
+        /* Get existing deployments for this app definition */
+        List<Deployment> existingDeployments = K8sUtil.getExistingDeployments(client.kubernetes(), client.namespace(),
+                appDefinitionResourceName, appDefinitionResourceUID);
+
+        /* Compute missing deployments */
+        Set<Integer> missingDeploymentIds = TheiaCloudDeploymentUtil.computeIdsOfMissingDeployments(appDefinition,
+                correlationId, instances, existingDeployments);
+
+        /* Create missing deployments for this app definition */
+        for (int instance : missingDeploymentIds) {
+            createAndApplyDeployment(client.kubernetes(), client.namespace(), correlationId, appDefinitionResourceName,
+                    appDefinitionResourceUID, instance, appDefinition, arguments.isUseKeycloak(), labelsToAdd);
+        }
+        return true;
+    }
+
     protected void createAndApplyService(NamespacedKubernetesClient client, String namespace, String correlationId,
             String appDefinitionResourceName, String appDefinitionResourceUID, int instance,
             AppDefinition appDefinition, boolean useOAuth2Proxy, Map<String, String> labelsToAdd) {