SOLR-17269: Do not publish synthetic solr core (of Coordinator node) to ZK

solr/CHANGES.txt

@@ -132,6 +132,8 @@ Optimizations
 
 * SOLR-17099: Do not return spurious tags when fetching metrics from a Solr node to another. (Pierre Salagnac)
 
+* SOLR-17269: Prevent the "Coordinator node" feature from registering synthetic cores in ZooKeeper (Patson Luk)
+
 Bug Fixes
 ---------------------
 * SOLR-12813: subqueries should respect basic auth. (Rudy Seitz via Eric Pugh)

solr/core/src/java/org/apache/solr/cloud/ZkConfigSetService.java

@@ -26,12 +26,9 @@
 import java.util.Map;
 import java.util.Objects;
 import org.apache.solr.client.solrj.cloud.SolrCloudManager;
-import org.apache.solr.cloud.api.collections.CreateCollectionCmd;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.cloud.SolrZkClient;
 import org.apache.solr.common.cloud.ZkMaintenanceUtils;
-import org.apache.solr.common.cloud.ZkStateReader;
-import org.apache.solr.common.cloud.ZooKeeperException;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.common.util.Utils;
 import org.apache.solr.core.ConfigSetProperties;
@@ -71,36 +68,18 @@ public ZkConfigSetService(SolrZkClient zkClient) {
 
   @Override
   public SolrResourceLoader createCoreResourceLoader(CoreDescriptor cd) {
-    final String colName = cd.getCollectionName();
-
-    // For back compat with cores that can create collections without the collections API
-    try {
-      if (!zkClient.exists(ZkStateReader.COLLECTIONS_ZKNODE + "/" + colName, true)) {
-        // TODO remove this functionality or maybe move to a CLI mechanism
-        log.warn(
-            "Auto-creating collection (in ZK) from core descriptor (on disk).  This feature may go away!");
-        CreateCollectionCmd.createCollectionZkNode(
-            zkController.getSolrCloudManager().getDistribStateManager(),
-            colName,
-            cd.getCloudDescriptor().getParams(),
-            zkController.getCoreContainer().getConfigSetService());
-      }
-    } catch (InterruptedException e) {
-      Thread.currentThread().interrupt();
-      throw new ZooKeeperException(
-          SolrException.ErrorCode.SERVER_ERROR, "Interrupted auto-creating collection", e);
-    } catch (KeeperException e) {
-      throw new ZooKeeperException(
-          SolrException.ErrorCode.SERVER_ERROR, "Failure auto-creating collection", e);
+    // Currently, cd.getConfigSet() is always null. Except that it's explicitly set by
+    // {@link org.apache.solr.core.SyntheticSolrCore}.
+    // Should we consider setting it for all cores as a part of CoreDescriptor creation/loading
+    // process?
+    if (cd.getConfigSet() == null) {
+      String configSetName =
+          zkController.getClusterState().getCollection(cd.getCollectionName()).getConfigName();
+      cd.setConfigSet(configSetName);
     }
 
-    // The configSet is read from ZK and populated.  Ignore CD's pre-existing configSet; only
-    // populated in standalone
-    String configSetName = zkController.getClusterState().getCollection(colName).getConfigName();
-    cd.setConfigSet(configSetName);
-
     return new ZkSolrResourceLoader(
-        cd.getInstanceDir(), configSetName, parentLoader.getClassLoader(), zkController);
+        cd.getInstanceDir(), cd.getConfigSet(), parentLoader.getClassLoader(), zkController);
   }
 
   @Override

solr/core/src/java/org/apache/solr/core/SolrCore.java

@@ -1235,7 +1235,7 @@ private SolrCore(
   }
 
   /** Set UpdateLog to buffer updates if the slice is in construction. */
-  private void bufferUpdatesIfConstructing(CoreDescriptor coreDescriptor) {
+  protected void bufferUpdatesIfConstructing(CoreDescriptor coreDescriptor) {
 
     if (coreContainer != null && coreContainer.isZooKeeperAware()) {
       if (reqHandlers.get("/get") == null) {

solr/core/src/java/org/apache/solr/core/SyntheticSolrCore.java

@@ -0,0 +1,75 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.solr.core;
+
+import java.nio.file.Path;
+import java.util.Map;
+import org.apache.solr.common.SolrException;
+import org.apache.solr.common.params.CoreAdminParams;
+import org.apache.solr.rest.RestManager;
+
+/**
+ * A synthetic core that is created only in memory and not registered against Zookeeper.
+ *
+ * <p>This is only used in Coordinator node to support a subset of SolrCore functionalities required
+ * by Coordinator operations such as aggregating and writing out response and providing configset
+ * info.
+ *
+ * <p>There should only be one instance of SyntheticSolrCore per configset
+ */
+public class SyntheticSolrCore extends SolrCore {
+  public SyntheticSolrCore(CoreContainer coreContainer, CoreDescriptor cd, ConfigSet configSet) {
+    super(coreContainer, cd, configSet);
+  }
+
+  public static SyntheticSolrCore createAndRegisterCore(
+      CoreContainer coreContainer, String syntheticCoreName, String configSetName) {
+    Map<String, String> coreProps = Map.of(CoreAdminParams.COLLECTION, syntheticCoreName);
+
+    CoreDescriptor syntheticCoreDescriptor =
+        new CoreDescriptor(
+            syntheticCoreName,
+            Path.of(coreContainer.getSolrHome(), syntheticCoreName),
+            coreProps,
+            coreContainer.getContainerProperties(),
+            coreContainer.getZkController());
+    syntheticCoreDescriptor.setConfigSet(configSetName);
+    ConfigSet coreConfig =
+        coreContainer.getConfigSetService().loadConfigSet(syntheticCoreDescriptor);
+    syntheticCoreDescriptor.setConfigSetTrusted(coreConfig.isTrusted());
+    SyntheticSolrCore syntheticCore =
+        new SyntheticSolrCore(coreContainer, syntheticCoreDescriptor, coreConfig);
+    coreContainer.registerCore(syntheticCoreDescriptor, syntheticCore, false, false);
+
+    return syntheticCore;
+  }
+
+  @Override
+  protected void bufferUpdatesIfConstructing(CoreDescriptor coreDescriptor) {
+    // no updates to SyntheticSolrCore
+  }
+
+  @Override
+  protected RestManager initRestManager() throws SolrException {
+    // returns an initialized RestManager. As init routines requires reading configname of the
+    // core's collection from ZK
+    // which synthetic core is not registered in ZK.
+    // We do not expect RestManager ops on Coordinator Nodes
+    return new RestManager();
+  }
+}