KAFKA-19719 --no-initial-controllers should not assume kraft.version=1 (#20604)

```
commit ec37eb5 (HEAD ->
KAFKA-19719-cherry-pick-41, origin/KAFKA-19719-cherry-pick-41)
Author: Kevin Wu <[email protected]>
Date:   Thu Sep 25 11:56:16 2025 -0500

    KAFKA-19719: --no-initial-controllers should not assume
kraft.version=1 (#20551)

    Just because a controller node sets --no-initial-controllers flag
does     not mean it is necessarily running kraft.version=1. The more
precise     meaning is that the controller node being formatted does not
know what     kraft version the cluster should be in, and therefore it
is only safe to     assume kraft.version=0. Only by setting
--standalone,--initial-controllers, or --no-initial-controllers     AND
not specifying the controller.quorum.voters static config, is it
known kraft.version > 0.

    For example, it is a valid configuration (although confusing) to run
a     static   quorum defined by controller.quorum.voters but have all
the     controllers   format with --no-initial-controllers. In this
case,     specifying --no-initial-controllers alongside a metadata
version that     does not  support kraft.version=1 causes formatting to
fail, which is     does not  support kraft.version=1 causes formatting
to fail, which is     a  regression.

    Additionally, the formatter should not check the kraft.version
against     the release version, since kraft.version does not actually
depend on any     release version. It should only check the
kraft.version against the     static voters config/format arguments.

    This PR also cleans up the integration test framework to match the
semantics of formatting an actual cluster.

    Reviewers: TengYao Chi <[email protected]>, Kuan-Po Tseng
<[email protected]>, Chia-Ping Tsai <[email protected]>, José Armando
García Sancio <[email protected]>      Conflicts:
core/src/main/scala/kafka/tools/StorageTool.scala Minor conflicts. Keep
changes from cherry-pick.
core/src/test/java/kafka/server/ReconfigurableQuorumIntegrationTest.java
Remove auto-join tests, since 4.1 does not support it. docs/ops.html
Keep docs section from cherry-pick.
metadata/src/test/java/org/apache/kafka/metadata/storage/FormatterTest.java
Minor conflicts. Keep cherry-picked changes.
test-common/test-common-runtime/src/main/java/org/apache/kafka/common/test/KafkaClusterTestKit.java
Conflicts due to integration test framework changes. Keep new changes.

commit 02d58b1 (upstream/4.1)
```

Reviewers: Chia-Ping Tsai <[email protected]>

Author: kevin-wu24

core/src/main/scala/kafka/tools/StorageTool.scala

@@ -135,21 +135,30 @@ object StorageTool extends Logging {
       featureNamesAndLevels(_).foreachEntry {
         (k, v) => formatter.setFeatureLevel(k, v)
       })
-    Option(namespace.getString("initial_controllers")).
+    val initialControllers = namespace.getString("initial_controllers")
+    val isStandalone = namespace.getBoolean("standalone")
+    val staticVotersEmpty = config.quorumConfig.voters().isEmpty
+    formatter.setHasDynamicQuorum(staticVotersEmpty)
+    if (!staticVotersEmpty && (Option(initialControllers).isDefined || isStandalone)) {
+      throw new TerseFailure("You cannot specify " +
+        QuorumConfig.QUORUM_VOTERS_CONFIG + " and format the node " +
+        "with --initial-controllers or --standalone. " +
+        "If you want to use dynamic quorum, please remove " +
+        QuorumConfig.QUORUM_VOTERS_CONFIG + " and specify " +
+        QuorumConfig.QUORUM_BOOTSTRAP_SERVERS_CONFIG + " instead.")
+    }
+    Option(initialControllers).
       foreach(v => formatter.setInitialControllers(DynamicVoters.parse(v)))
-    if (namespace.getBoolean("standalone")) {
+    if (isStandalone) {
       formatter.setInitialControllers(createStandaloneDynamicVoters(config))
     }
-    if (namespace.getBoolean("no_initial_controllers")) {
-      formatter.setNoInitialControllersFlag(true)
-    } else {
-      if (config.processRoles.contains(ProcessRole.ControllerRole)) {
-        if (config.quorumConfig.voters().isEmpty && formatter.initialVoters().isEmpty) {
+    if (!namespace.getBoolean("no_initial_controllers") &&
+      config.processRoles.contains(ProcessRole.ControllerRole) &&
+      staticVotersEmpty &&
+      formatter.initialVoters().isEmpty) {
           throw new TerseFailure("Because " + QuorumConfig.QUORUM_VOTERS_CONFIG +
             " is not set on this controller, you must specify one of the following: " +
             "--standalone, --initial-controllers, or --no-initial-controllers.");
-        }
-      }
     }
     Option(namespace.getList("add_scram")).
       foreach(scramArgs => formatter.setScramArguments(scramArgs.asInstanceOf[util.List[String]]))
@@ -319,18 +328,21 @@ object StorageTool extends Logging {
 
     val reconfigurableQuorumOptions = formatParser.addMutuallyExclusiveGroup()
     reconfigurableQuorumOptions.addArgument("--standalone", "-s")
-      .help("Used to initialize a controller as a single-node dynamic quorum.")
+      .help("Used to initialize a controller as a single-node dynamic quorum. When setting this flag, " +
+        "the controller.quorum.voters config must not be set, and controller.quorum.bootstrap.servers is set instead.")
       .action(storeTrue())
 
     reconfigurableQuorumOptions.addArgument("--no-initial-controllers", "-N")
-      .help("Used to initialize a server without a dynamic quorum topology.")
+      .help("Used to initialize a server without specifying a dynamic quorum. When setting this flag, " +
+        "the controller.quorum.voters config should not be set, and controller.quorum.bootstrap.servers is set instead.")
       .action(storeTrue())
 
     reconfigurableQuorumOptions.addArgument("--initial-controllers", "-I")
-      .help("Used to initialize a server with a specific dynamic quorum topology. The argument " +
+      .help("Used to initialize a server with the specified dynamic quorum. The argument " +
         "is a comma-separated list of id@hostname:port:directory. The same values must be used to " +
         "format all nodes. For example:\n[email protected]:8082:JEXY6aqzQY-32P5TStzaFg,[email protected]:8083:" +
-        "MvDxzVmcRsaTz33bUuRU6A,[email protected]:8084:07R5amHmR32VDA6jHkGbTA\n")
+        "MvDxzVmcRsaTz33bUuRU6A,[email protected]:8084:07R5amHmR32VDA6jHkGbTA\n. When setting this flag, " +
+        "the controller.quorum.voters config must not be set, and controller.quorum.bootstrap.servers is set instead.")
       .action(store())
   }
 

core/src/test/java/kafka/server/ReconfigurableQuorumIntegrationTest.java

@@ -29,6 +29,7 @@
 
 import org.junit.jupiter.api.Test;
 
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
@@ -83,9 +84,8 @@ public void testCreateAndDestroyReconfigurableCluster() throws Exception {
             new TestKitNodes.Builder().
                 setNumBrokerNodes(1).
                 setNumControllerNodes(1).
-                setFeature(KRaftVersion.FEATURE_NAME, KRaftVersion.KRAFT_VERSION_1.featureLevel()).
                 build()
-        ).build()) {
+        ).setStandalone(true).build()) {
             cluster.format();
             cluster.startup();
             try (Admin admin = Admin.create(cluster.clientProperties())) {
@@ -107,13 +107,23 @@ static Map<Integer, Uuid> findVoterDirs(Admin admin) throws Exception {
 
     @Test
     public void testRemoveController() throws Exception {
-        try (KafkaClusterTestKit cluster = new KafkaClusterTestKit.Builder(
-            new TestKitNodes.Builder().
-                setNumBrokerNodes(1).
-                setNumControllerNodes(3).
-                setFeature(KRaftVersion.FEATURE_NAME, KRaftVersion.KRAFT_VERSION_1.featureLevel()).
-                build()
-        ).build()) {
+        final var nodes = new TestKitNodes.Builder().
+            setNumBrokerNodes(1).
+            setNumControllerNodes(3).
+            build();
+
+        final Map<Integer, Uuid> initialVoters = new HashMap<>();
+        for (final var controllerNode : nodes.controllerNodes().values()) {
+            initialVoters.put(
+                controllerNode.id(),
+                controllerNode.metadataDirectoryId()
+            );
+        }
+
+        try (KafkaClusterTestKit cluster = new KafkaClusterTestKit.Builder(nodes).
+            setInitialVoterSet(initialVoters).
+            build()
+        ) {
             cluster.format();
             cluster.startup();
             try (Admin admin = Admin.create(cluster.clientProperties())) {
@@ -132,12 +142,22 @@ public void testRemoveController() throws Exception {
 
     @Test
     public void testRemoveAndAddSameController() throws Exception {
-        try (KafkaClusterTestKit cluster = new KafkaClusterTestKit.Builder(
-            new TestKitNodes.Builder().
-                setNumBrokerNodes(1).
-                setNumControllerNodes(4).
-                setFeature(KRaftVersion.FEATURE_NAME, KRaftVersion.KRAFT_VERSION_1.featureLevel()).
-                build()).build()
+        final var nodes = new TestKitNodes.Builder().
+            setNumBrokerNodes(1).
+            setNumControllerNodes(4).
+            build();
+
+        final Map<Integer, Uuid> initialVoters = new HashMap<>();
+        for (final var controllerNode : nodes.controllerNodes().values()) {
+            initialVoters.put(
+                controllerNode.id(),
+                controllerNode.metadataDirectoryId()
+            );
+        }
+
+        try (KafkaClusterTestKit cluster = new KafkaClusterTestKit.Builder(nodes).
+            setInitialVoterSet(initialVoters).
+            build()
         ) {
             cluster.format();
             cluster.startup();

core/src/test/scala/integration/kafka/server/KRaftClusterTest.scala

@@ -1011,8 +1011,7 @@ class KRaftClusterTest {
     val cluster = new KafkaClusterTestKit.Builder(
       new TestKitNodes.Builder().
         setNumBrokerNodes(1).
-        setNumControllerNodes(1).
-        setFeature(KRaftVersion.FEATURE_NAME, 1.toShort).build()).build()
+        setNumControllerNodes(1).build()).setStandalone(true).build()
     try {
       cluster.format()
       cluster.startup()

core/src/test/scala/unit/kafka/tools/StorageToolTest.scala

@@ -375,7 +375,10 @@ Found problem:
   def testFormatWithStandaloneFlagOnBrokerFails(): Unit = {
     val availableDirs = Seq(TestUtils.tempDir())
     val properties = new Properties()
-    properties.putAll(defaultStaticQuorumProperties)
+    properties.setProperty("process.roles", "broker")
+    properties.setProperty("node.id", "0")
+    properties.setProperty("controller.listener.names", "CONTROLLER")
+    properties.setProperty("controller.quorum.bootstrap.servers", "localhost:9093")
     properties.setProperty("log.dirs", availableDirs.mkString(","))
     val stream = new ByteArrayOutputStream()
     val arguments = ListBuffer[String]("--release-version", "3.9-IV0", "--standalone")
@@ -458,19 +461,14 @@ Found problem:
               Seq("--release-version", "3.9-IV0"))).getMessage)
   }
 
-  @ParameterizedTest
-  @ValueSource(booleans = Array(false, true))
-  def testFormatWithNoInitialControllersSucceedsOnController(setKraftVersionFeature: Boolean): Unit = {
+  @Test
+  def testFormatWithNoInitialControllersSucceedsOnController(): Unit = {
     val availableDirs = Seq(TestUtils.tempDir())
     val properties = new Properties()
     properties.putAll(defaultDynamicQuorumProperties)
     properties.setProperty("log.dirs", availableDirs.mkString(","))
     val stream = new ByteArrayOutputStream()
     val arguments = ListBuffer[String]("--release-version", "3.9-IV0", "--no-initial-controllers")
-    if (setKraftVersionFeature) {
-      arguments += "--feature"
-      arguments += "kraft.version=1"
-    }
     assertEquals(0, runFormatCommand(stream, properties, arguments.toSeq))
     assertTrue(stream.toString().
       contains("Formatting metadata directory %s".format(availableDirs.head)),

docs/ops.html

@@ -4089,14 +4089,8 @@ <h5 class="anchor-heading"><a id="static_versus_dynamic_kraft_quorums" class="an
   <p>
     The static versus dynamic nature of the quorum is determined at the time of formatting.
     Specifically, the quorum will be formatted as dynamic if <code>controller.quorum.voters</code> is
-    <b>not</b> present, and if the software version is Apache Kafka 3.9 or newer. If you have
-    followed the instructions earlier in this document, you will get a dynamic quorum.<p>
-
-    If you would like the formatting process to fail if a dynamic quorum cannot be achieved, format your
-    controllers using the <code>--feature kraft.version=1</code>. (Note that you should not supply
-    this flag when formatting brokers -- only when formatting controllers.)<p>
-
-  <pre><code class="language-bash">$ bin/kafka-storage.sh format -t KAFKA_CLUSTER_ID --feature kraft.version=1 -c controller.properties</code></pre>
+    <b>not</b> present, and one of --standalone, --initial-controllers, or --no-initial-controllers is set.
+    If you have followed the instructions earlier in this document, you will get a dynamic quorum.
   <p>
   Note: To migrate from static voter set to dynamic voter set, please refer to the <a href="#kraft_upgrade">Upgrade</a> section.
 

metadata/src/main/java/org/apache/kafka/metadata/storage/Formatter.java

@@ -131,7 +131,7 @@ public class Formatter {
      * The initial KIP-853 voters.
      */
     private Optional<DynamicVoters> initialControllers = Optional.empty();
-    private boolean noInitialControllersFlag = false;
+    private boolean hasDynamicQuorum = false;
 
     public Formatter setPrintStream(PrintStream printStream) {
         this.printStream = printStream;
@@ -217,8 +217,8 @@ public Formatter setInitialControllers(DynamicVoters initialControllers) {
         return this;
     }
 
-    public Formatter setNoInitialControllersFlag(boolean noInitialControllersFlag) {
-        this.noInitialControllersFlag = noInitialControllersFlag;
+    public Formatter setHasDynamicQuorum(boolean hasDynamicQuorum) {
+        this.hasDynamicQuorum = hasDynamicQuorum;
         return this;
     }
 
@@ -227,7 +227,7 @@ public Optional<DynamicVoters> initialVoters() {
     }
 
     boolean hasDynamicQuorum() {
-        return initialControllers.isPresent() || noInitialControllersFlag;
+        return hasDynamicQuorum;
     }
 
     public BootstrapMetadata bootstrapMetadata() {
@@ -337,8 +337,8 @@ Map<String, Short> calculateEffectiveFeatureLevels() {
     /**
      * Calculate the effective feature level for kraft.version. In order to keep existing
      * command-line invocations of StorageTool working, we default this to 0 if no dynamic
-     * voter quorum arguments were provided. As a convenience, if dynamic voter quorum arguments
-     * were passed, we set the latest kraft.version. (Currently there is only 1 non-zero version).
+     * voter quorum arguments were provided. As a convenience, if the static voters config is
+     * empty, we set the latest kraft.version. (Currently there is only 1 non-zero version).
      *
      * @param configuredKRaftVersionLevel   The configured level for kraft.version
      * @return                              The effective feature level.
@@ -348,20 +348,19 @@ private short effectiveKRaftFeatureLevel(Optional<Short> configuredKRaftVersionL
             if (configuredKRaftVersionLevel.get() == 0) {
                 if (hasDynamicQuorum()) {
                     throw new FormatterException(
-                        "Cannot set kraft.version to " +
-                        configuredKRaftVersionLevel.get() +
-                        " if one of the flags --standalone, --initial-controllers, or --no-initial-controllers is used. " +
-                        "For dynamic controllers support, try removing the --feature flag for kraft.version."
+                        "Cannot set kraft.version to 0 if controller.quorum.voters is empty and one of the flags " +
+                        "--standalone, --initial-controllers, or --no-initial-controllers is used. For dynamic " +
+                        "controllers support, try removing the --feature flag for kraft.version."
                     );
                 }
             } else {
                 if (!hasDynamicQuorum()) {
                     throw new FormatterException(
-                        "Cannot set kraft.version to " +
-                        configuredKRaftVersionLevel.get() +
-                        " unless one of the flags --standalone, --initial-controllers, or --no-initial-controllers is used. " +
-                        "For dynamic controllers support, try using one of --standalone, --initial-controllers, or " +
-                        "--no-initial-controllers."
+                        "Cannot set kraft.version to " + configuredKRaftVersionLevel.get() +
+                        " unless controller.quorum.voters is empty and one of the flags --standalone, " +
+                        "--initial-controllers, or --no-initial-controllers is used. " +
+                        "For dynamic controllers support, try using one of --standalone, --initial-controllers, " +
+                        "or --no-initial-controllers and removing controller.quorum.voters."
                     );
                 }
             }