NIFI-926:

- Ensuring that nodes are not disconnected when the user attempts to reset a counter that does not exist on that node. This can happen when/if counters are adjusted conditionally.

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-framework-cluster/src/main/java/org/apache/nifi/cluster/manager/impl/WebClusterManager.java

@@ -309,6 +309,7 @@ public class WebClusterManager implements HttpClusterManager, ProtocolHandler, C
     public static final Pattern PROVENANCE_QUERY_URI = Pattern.compile("/nifi-api/controller/provenance/[a-f0-9\\-]{36}");
     public static final Pattern PROVENANCE_EVENT_URI = Pattern.compile("/nifi-api/controller/provenance/events/[0-9]+");
 
+    public static final Pattern COUNTERS_URI = Pattern.compile("/nifi-api/controller/counters/[a-f0-9\\-]{36}");
     public static final String CONTROLLER_SERVICES_URI = "/nifi-api/controller/controller-services/node";
     public static final Pattern CONTROLLER_SERVICE_URI_PATTERN = Pattern.compile("/nifi-api/controller/controller-services/node/[a-f0-9\\-]{36}");
     public static final Pattern CONTROLLER_SERVICE_REFERENCES_URI_PATTERN = Pattern.compile("/nifi-api/controller/controller-services/node/[a-f0-9\\-]{36}/references");
@@ -2424,6 +2425,10 @@ public class WebClusterManager implements HttpClusterManager, ProtocolHandler, C
         return "GET".equalsIgnoreCase(method) && PROVENANCE_EVENT_URI.matcher(uri.getPath()).matches();
     }
 
+    private static boolean isCountersEndpoint(final URI uri) {
+        return COUNTERS_URI.matcher(uri.getPath()).matches();
+    }
+
     private static boolean isControllerServicesEndpoint(final URI uri, final String method) {
         return "GET".equalsIgnoreCase(method) && CONTROLLER_SERVICES_URI.equals(uri.getPath());
     }
@@ -3227,6 +3232,19 @@ public class WebClusterManager implements HttpClusterManager, ProtocolHandler, C
          */
         if (mutableRequest) {
 
+            // if some (not all) nodes had a problematic response because of a missing counter, ensure the are not disconnected
+            if (!problematicNodeResponses.isEmpty() && problematicNodeResponses.size() < nodeResponses.size() && isMissingCounter(problematicNodeResponses, uri)) {
+                for (final Map.Entry<Node, NodeResponse> updatedNodeEntry : updatedNodesMap.entrySet()) {
+                    final NodeResponse nodeResponse = updatedNodeEntry.getValue();
+                    final Node node = updatedNodeEntry.getKey();
+
+                    if (problematicNodeResponses.contains(nodeResponse)) {
+                        node.setStatus(Status.CONNECTED);
+                        problematicNodeResponses.remove(nodeResponse);
+                    }
+                }
+            }
+
             // set the updated nodes
             nodes.removeAll(updatedNodesMap.keySet());
             nodes.addAll(updatedNodesMap.keySet());
@@ -3251,6 +3269,28 @@ public class WebClusterManager implements HttpClusterManager, ProtocolHandler, C
         return clientResponse;
     }
 
+    /**
+     * Determines if all problematic responses were due to 404 NOT_FOUND. Assumes that problematicNodeResponses is not empty and
+     * is not comprised of responses from all nodes in the cluster (at least one node contained the counter in question).
+     *
+     * @param problematicNodeResponses  The problematic node responses
+     * @param uri                       The URI for the request
+     * @return                          Whether all problematic node responses were due to a missing counter
+     */
+    private boolean isMissingCounter(final Set<NodeResponse> problematicNodeResponses, final URI uri) {
+        if (isCountersEndpoint(uri)) {
+            boolean notFound = true;
+            for (final NodeResponse problematicResponse : problematicNodeResponses) {
+                if (problematicResponse.getStatus() != 404) {
+                    notFound = false;
+                    break;
+                }
+            }
+            return notFound;
+        }
+        return false;
+    }
+
     /**
      * Drains the node responses off of the socket to ensure that the socket is appropriately cleaned-up.
      *