SOLR-16475 Make the default replica placement plugin configurable (ap…

…ache#1089)

solr/CHANGES.txt

@@ -68,6 +68,8 @@ Improvements
 * SOLR-15478: A v2 equivalent of CLUSTERSTATUS command is now available at `GET /api/cluster`. Collection listing,
   previously at this path, can still be accessed at `GET /api/collections`. (Joshua Ouma via Jason Gerlowski)
 
+* SOLR-16475: Make the default replica placement plugin configurable as system property on startup (janhoy)
+
 * SOLR-13626: Document the SystemInfoHandler in the Ref Guide.  (Tony Cook via Eric Pugh)
 
 * SOLR-15479: A v2 equivalent of the RENAME command is now available at `POST /api/collections/collName/rename`. (Anakhe Ajayi via Jason Gerlowski)

solr/bin/solr

@@ -1804,6 +1804,11 @@ if [[ -n "${SOLR_MODULES:-}" ]] ; then
   SOLR_OPTS+=("-Dsolr.modules=$SOLR_MODULES")
 fi
 
+# Default placement plugin
+if [[ -n "${SOLR_PLACEMENTPLUGIN_DEFAULT:-}" ]] ; then
+  SOLR_OPTS+=("-Dsolr.placementplugin.default=$SOLR_PLACEMENTPLUGIN_DEFAULT")
+fi
+
 : ${SOLR_SERVER_DIR:=$DEFAULT_SERVER_DIR}
 
 if [ ! -e "$SOLR_SERVER_DIR" ]; then

solr/bin/solr.cmd

@@ -987,6 +987,11 @@ IF DEFINED SOLR_MODULES (
   set "SOLR_OPTS=%SOLR_OPTS% -Dsolr.modules=%SOLR_MODULES%"
 )
 
+REM Default placement plugin
+IF DEFINED SOLR_PLACEMENTPLUGIN_DEFAULT (
+  set "SOLR_OPTS=%SOLR_OPTS% -Dsolr.placementplugin.default=%SOLR_PLACEMENTPLUGIN_DEFAULT%"
+)
+
 IF "%SOLR_SERVER_DIR%"=="" set "SOLR_SERVER_DIR=%DEFAULT_SERVER_DIR%"
 
 IF NOT EXIST "%SOLR_SERVER_DIR%" (

solr/bin/solr.in.cmd

@@ -236,4 +236,8 @@ REM then enable the following setting to address CVE-2021-44228
 REM set SOLR_OPTS=%SOLR_OPTS% -Dlog4j2.formatMsgNoLookups=true
 
 REM The bundled plugins in the "modules" folder can easily be enabled as a comma-separated list in SOLR_MODULES variable
-REM set SOLR_MODULES=extraction,ltr
+REM set SOLR_MODULES=extraction,ltr
+
+REM Configure the default replica placement plugin to use if one is not configured in cluster properties
+REM See https://solr.apache.org/guide/solr/latest/configuration-guide/replica-placement-plugins.html for details
+REM set SOLR_PLACEMENTPLUGIN_DEFAULT=simple

solr/bin/solr.in.sh

@@ -281,3 +281,7 @@
 
 # The bundled plugins in the "modules" folder can easily be enabled as a comma-separated list in SOLR_MODULES variable
 # SOLR_MODULES=extraction,ltr
+
+# Configure the default replica placement plugin to use if one is not configured in cluster properties
+# See https://solr.apache.org/guide/solr/latest/configuration-guide/replica-placement-plugins.html for details
+#SOLR_PLACEMENTPLUGIN_DEFAULT=simple

solr/core/src/java/org/apache/solr/cloud/api/collections/Assign.java

@@ -41,6 +41,9 @@
 import org.apache.solr.client.solrj.cloud.VersionedData;
 import org.apache.solr.cluster.placement.PlacementPlugin;
 import org.apache.solr.cluster.placement.impl.PlacementPluginAssignStrategy;
+import org.apache.solr.cluster.placement.plugins.AffinityPlacementFactory;
+import org.apache.solr.cluster.placement.plugins.MinimizeCoresPlacementFactory;
+import org.apache.solr.cluster.placement.plugins.RandomPlacementFactory;
 import org.apache.solr.cluster.placement.plugins.SimplePlacementFactory;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.cloud.ClusterState;
@@ -63,6 +66,7 @@
 public class Assign {
   private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
   public static final String SYSTEM_COLL_PREFIX = ".sys.";
+  public static final String PLACEMENTPLUGIN_DEFAULT_SYSPROP = "solr.placementplugin.default";
 
   public static String getCounterNodePath(String collection) {
     return ZkStateReader.COLLECTIONS_ZKNODE + "/" + collection + "/counter";
@@ -562,8 +566,37 @@ public static AssignStrategy createAssignStrategy(CoreContainer coreContainer) {
         coreContainer.getPlacementPluginFactory().createPluginInstance();
     if (placementPlugin == null) {
       // Otherwise use the default
-      // TODO: Replace this with a better options, such as the AffinityPlacementFactory
-      placementPlugin = (new SimplePlacementFactory()).createPluginInstance();
+      String defaultPluginId = System.getProperty(PLACEMENTPLUGIN_DEFAULT_SYSPROP);
+      if (defaultPluginId != null) {
+        switch (defaultPluginId.toLowerCase(Locale.ROOT)) {
+          case "simple":
+            placementPlugin = (new SimplePlacementFactory()).createPluginInstance();
+            break;
+          case "affinity":
+            placementPlugin = (new AffinityPlacementFactory()).createPluginInstance();
+            break;
+          case "minimizecores":
+            placementPlugin = (new MinimizeCoresPlacementFactory()).createPluginInstance();
+            break;
+          case "random":
+            placementPlugin = (new RandomPlacementFactory()).createPluginInstance();
+            break;
+          default:
+            throw new SolrException(
+                SolrException.ErrorCode.SERVER_ERROR,
+                "Invalid value for system property '"
+                    + PLACEMENTPLUGIN_DEFAULT_SYSPROP
+                    + "'. Supported values are 'simple', 'random', 'affinity' and 'minimizecores'");
+        }
+        log.info(
+            "Default replica placement plugin set in {} to {}",
+            PLACEMENTPLUGIN_DEFAULT_SYSPROP,
+            defaultPluginId);
+      } else {
+        // TODO: Consider making the ootb default AffinityPlacementFactory, see
+        // https://issues.apache.org/jira/browse/SOLR-16492
+        placementPlugin = (new SimplePlacementFactory()).createPluginInstance();
+      }
     }
     return new PlacementPluginAssignStrategy(placementPlugin);
   }

solr/packaging/build.gradle

@@ -159,10 +159,9 @@ assemble.dependsOn installDist
 
 task downloadBats(type: NpmTask) {
   group = 'Build Dependency Download'
-  args = ["install", "[email protected]",
-                     "ztombol/bats-support#v0.2.0",
-                     "ztombol/bats-assert#v0.3.0",
-                     "ztombol/bats-file#v0.2.0",
+  args = ["install", "https://github.com/bats-core/bats-core#v1.8.2",
+                     "https://github.com/bats-core/bats-assert#v2.0.0",
+                     "https://github.com/bats-core/bats-file#v0.3.0",
   ]
 
   inputs.files("${project.ext.nodeProjectDir}/package.json")

solr/packaging/test/bats_helper.bash

@@ -20,7 +20,7 @@
 #   The SOLR_HOME directory will be cleared when the next test file is executed.
 # - "setup" should use "common_setup" if a Solr process is NOT being started in that same "setup" function.
 common_setup() {
-    bats_require_minimum_version 1.8.0
+    bats_require_minimum_version 1.8.2
 
     if [ -z ${BATS_LIB_PREFIX:-} ]; then
         # Debugging help, if you want to run bats directly, try to detect where libraries might be

solr/packaging/test/test_placement_plugin.bats

@@ -0,0 +1,47 @@
+#!/usr/bin/env bats
+
+# 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.
+
+load bats_helper
+
+setup() {
+  common_clean_setup
+}
+
+teardown() {
+  # save a snapshot of SOLR_HOME for failed tests
+  save_home_on_failure
+
+  delete_all_collections
+  solr stop -all >/dev/null 2>&1
+}
+
+@test "Affinity placement plugin using sysprop" {
+  run solr start -c -Dsolr.placementplugin.default=affinity
+  solr assert -c http://localhost:8983/solr -t 3000
+  run solr create_collection -c COLL_NAME
+  collection_exists COLL_NAME
+  assert_file_contains ${SOLR_LOGS_DIR}/solr.log 'Default replica placement plugin set in solr\.placementplugin\.default to affinity'
+}
+
+@test "Affinity placement plugin using ENV" {
+  export SOLR_PLACEMENTPLUGIN_DEFAULT=random
+  run solr start -c
+  solr assert -c http://localhost:8983/solr -t 3000
+  run solr create_collection -c COLL_NAME
+  collection_exists COLL_NAME
+  assert_file_contains ${SOLR_LOGS_DIR}/solr.log 'Default replica placement plugin set in solr\.placementplugin\.default to random'
+}

solr/solr-ref-guide/modules/configuration-guide/pages/replica-placement-plugins.adoc

@@ -34,7 +34,11 @@ The configuration entry may also contain a `config` element if the plugin implem
 
 == Placement Plugins Included with Solr
 The following placement plugins are available out-of-the-box in Solr 9.0.
-If no placement plugin is defined, Solr will default to using the <<#simpleplacementfactory,SimplePlacementPlugin>>.
+If no placement plugin is defined in cluster properties, Solr will default to using
+the plugin configured in system property `solr.placementplugin.default` or environment
+variable `SOLR_PLACEMENTPLUGIN_DEFAULT`. Supported values are `simple`, `random`, `affinity`
+and `minimizecores`. If no such property or environment variable is set,
+the <<#simpleplacementfactory,SimplePlacementPlugin>> is used.
 
 In order to use a plugin its configuration must be added using the `/cluster/plugin` API.
 For example, in order to use the `AffinityPlacementFactory` plugin the following command should be executed: