Upgrading

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Upgrading to 4.2.0

Upgrading Servers to 4.2.0 from any version 3.3.x through 4.1.x

Notable changes in 4.2.0

  • The --max-partition-memory-bytes option in kafka-console-producer is deprecated and will be removed in Kafka 5.0. Please use --batch-size instead.
  • Queues for Kafka (KIP-932) is production-ready in Apache Kafka 4.2. This feature introduces a new kind of group called share groups, as an alternative to consumer groups. Consumers in a share group cooperatively consume records from topics, without assigning each partition to just one consumer. Share groups also introduce per-record acknowledgement and counting of delivery attempts. Use share groups in cases where records are processed one at a time, rather than as part of an ordered stream.
  • The org.apache.kafka.common.header.internals.RecordHeader class has been updated to be read thread-safe. See KIP-1205 for details. In other words, each individual Header object within a ConsumerRecord’s headers can now be safely read from multiple threads concurrently.
  • The org.apache.kafka.disallowed.login.modules config was deprecated. Please use the org.apache.kafka.allowed.login.modules instead.
  • The remote.log.manager.thread.pool.size config was deprecated. Please use the remote.log.manager.follower.thread.pool.size instead.
  • The KafkaPrincipalBuilder now extends KafkaPrincipalSerde. Force developer to implement KafkaPrincipalSerde interface for custom KafkaPrincipalBuilder. For further details, please refer to KIP-1157.
  • The behavior of org.apache.kafka.streams.KafkaStreams#removeStreamThread has been changed. The consumer has no longer remove once removeStreamThread finished. Instead, consumer would be kicked off from the group after org.apache.kafka.streams.processor.internals.StreamThread completes its run function.
  • The support for MX4J library, enabled through kafka_mx4jenable system property, was deprecated and will be removed in Kafka 5.0.
  • The PARTITIONER_ADPATIVE_PARTITIONING_ENABLE_CONFIG in ProducerConfig was deprecated and will be removed in Kafka 5.0. Please use the PARTITIONER_ADAPTIVE_PARTITIONING_ENABLE_CONFIG instead.
  • The ConsumerPerformance command line tool has a new --include option that is an alternative to the --topic option. This new option allows to pass a regular expression specifying a list of topics to include for consumption, which is useful to test consumer performance across multiple topics or dynamically matching topic sets.
  • The consistency of argument names for the command-line tools has been improved (KIP-1147). The deprecated options will be removed in Kafka 5.0.
    • In kafka-producer-perf-test.sh, --bootstrap-server and --reporting-interval option are added.
    • In kafka-console-consumer.sh and kafka-console-share-consumer.sh, the option --property which is used to specify the properties for the formatter is deprecated in favor of --formatter-property.
    • In kafka-console-producer.sh, the option --property which is used to specify properties in the form key=value to the message reader is deprecated in favor of --reader-property.
    • In kafka-consumer-perf-test.sh and kafka-share-consumer-perf-test.sh, the option --messages is deprecated in favor of --num-records to bring all performance testing tools in line.
    • The option --command-property is used for all command-line tools which accept configuration properties directly on the command line. The tools affected are:
      • kafka-console-consumer.sh, kafka-console-producer.sh and kafka-console-share-consumer.sh (--consumer-property and --producer-property are deprecated in favor of --command-property)
      • kafka-producer-perf-test.sh (--producer-props is deprecated in favor of --command-property)
      • kafka-consumer-perf-test.sh and kafka-share-consumer-perf-test.sh gain the --command-property option to bring all performance testing tools in line
    • The option --command-config is used for all command-line tools which accept a file of configuration properties. The tools affected are:
      • kafka-cluster.sh (--config is deprecated in favor of --command-config)
      • kafka-console-consumer.sh, kafka-console-producer.sh and kafka-console-share-consumer.sh (--consumer.config and --producer.config are deprecated in favor of --command-config)
      • kafka-consumer-perf-test.sh, kafka-producer-perf-test.sh and kafka-share-consumer-perf-test.sh (--consumer.config and --producer.config are deprecated in favor of --command-config)
      • kafka-verifiable-consumer.sh and kafka-verifiable-producer.sh (--consumer.config and --producer.config are deprecated in favor of --command-config)
      • kafka-leader-election.sh (--admin.config is deprecated in favor of --command-config)
      • kafka-streams-application-reset.sh (--config-file is deprecated in favor of --command-config)
  • The num.replica.fetchers config has a new lower bound of 1.
  • Improvements have been made to the validation rules and default values of LIST-type configurations (KIP-1161).
    • LIST-type configurations now enforce stricter validation:
      • Null values are no longer accepted for most LIST-type configurations. Exceptions apply only to configurations that have null as their default value, as users cannot explicitly assign null values in configuration files or through the API.
      • Most LIST-type configurations no longer accept duplicate entries, except in cases where duplicates are explicitly supported. For backward compatibility, if users configure duplicate entries when they are not accepted, duplicate entries will be ignored and a warning will be logged.
      • For certain configurations, an empty list causes the system to malfunction. Therefore, empty lists are no longer allowed for those configurations.
    • Several configurations have been reclassified from STRING-type to LIST-type to better reflect their intended use as comma-separated values.
    • Default values for certain configurations have been adjusted to ensure better consistency with related settings.
    • cleanup.policy now supports empty values, which means infinite retention. This is equivalent to setting retention.ms=-1 and retention.bytes=-1
      If cleanup.policy is empty and remote.storage.enable is set to true, the local log segments will be cleaned based on the values of log.local.retention.bytes and log.local.retention.ms.
      If cleanup.policy is empty and remote.storage.enable is set to false, local log segments will not be deleted automatically. However, records can still be deleted explicitly through deleteRecords API calls, which will advance the log start offset and remove the corresponding log segments.
  • The controller.quorum.auto.join.enable has been added to QuorumConfig, enabling KRaft controllers to automatically join the cluster’s voter set, and defaults to false. For further details, please refer to KIP-853.
  • The AppInfo metrics will deprecate the following metric names, which will be removed in Kafka 5.0:
    • [name=start-time-ms, group=app-info, description=Metric indicating start-time-ms, tags={}]
    • [name=commit-id, group=app-info, description=Metric indicating commit-id, tags={}]
    • [name=version, group=app-info, description=Metric indicating version, tags={}] In addition, the client-id will be added to the tags of these metrics. The new metric names will be:
    • [name=start-time-ms, group=app-info, description=Metric indicating start-time-ms, tags={client-id=...}]
    • [name=commit-id, group=app-info, description=Metric indicating commit-id, tags={client-id=...}]
    • [name=version, group=app-info, description=Metric indicating version, tags={client-id=...}] For further details, please refer to KIP-1120.
  • The metrics org.apache.kafka.server:type=AssignmentsManager.QueuedReplicaToDirAssignments, org.apache.kafka.storage.internals.log:type=RemoteStorageThreadPool.RemoteLogReaderTaskQueueSize, and org.apache.kafka.storage.internals.log:type=RemoteStorageThreadPool.RemoteLogReaderAvgIdlePercent have been deprecated and will be removed in Kafka 5.0. As replacements, the following metrics have been introduced, which report the same information: kafka.server:type=AssignmentsManager.QueuedReplicaToDirAssignments, kafka.log.remote:type=RemoteStorageThreadPool.RemoteLogReaderTaskQueueSize, and kafka.log.remote:type=RemoteStorageThreadPool.RemoteLogReaderAvgIdlePercent. For further details, please refer to KIP-1100.
  • A new metric AvgIdleRatio has been added to the ControllerEventManager and MetadataLoader groups. These metrics measure the average idle ratio of their respective event queue threads, providing visibility into how much time each component spends waiting for events versus processing them. The metric value ranges from 0.0 (always busy) to 1.0 (always idle).
  • Deprecated org.apache.kafka.streams.KafkaStreams$CloseOptions and its related methods, such as KafkaStreams#close(org.apache.kafka.streams.KafkaStreams$CloseOptions). As a replacement, please use org.apache.kafka.streams.CloseOptions and KafkaStreams#close(org.apache.kafka.streams.CloseOptions). For further details, please refer to KIP-1153.
  • A new implementation of ConnectorClientConfigOverridePolicy, AllowlistConnectorClientConfigOverridePolicy, has been added. This enables specifying the configurations that connectors can override via connector.client.config.override.allowlist. From Kafka 5.0.0, this will be the default connector.client.config.override.policy policy. The PrincipalConnectorClientConfigOverridePolicy policy is now deprecated and will be removed in Kafka 5.0.0. For further details, please refer to KIP-1188.
  • It is now possible to specify the start time for a Kafka Streams punctuation, instead of relying on the non-deterministic time when you register it. For further details, please refer to KIP-1146.
  • Added an optional --node-id flag to the FeatureCommand command. It specifies the node to describe. If not provided, an arbitrary node is used.

Upgrading to 4.1.0

Note: Kafka Streams 4.1.0 contains a critical memory leak bug (KAFKA-19748) that affects users of range scans and certain DSL operators (session windows, sliding windows, stream-stream joins, foreign-key joins). Users running Kafka Streams should consider upgrading directly to 4.1.1, which includes the fix for it.

Upgrading Servers to 4.1.0 from any version 3.3.x through 4.0.x

Notable changes in 4.1.0

  • Apache Kafka 4.1 ships with a preview of Queues for Kafka (KIP-932). This feature introduces a new kind of group called share groups, as an alternative to consumer groups. Consumers in a share group cooperatively consume records from topics, without assigning each partition to just one consumer. Share groups also introduce per-record acknowledgement and counting of delivery attempts. Use share groups in cases where records are processed one at a time, rather than as part of an ordered stream. To enable share groups, use the kafka-features.sh tool to upgrade to share.version=1. For more information, please read the release notes.
  • Common
    • The logger class name for LogCleaner has been updated from kafka.log.LogCleaner to org.apache.kafka.storage.internals.log.LogCleaner in the log4j2.yaml configuration file. Added loggers for org.apache.kafka.storage.internals.log.LogCleaner$CleanerThread and org.apache.kafka.storage.internals.log.Cleaner classes to CleanerAppender.
    • The filename for rotated state-change.log files has been updated from stage-change.log.[date] to state-change.log.[date] in the log4j2.yaml configuration file.
  • Broker
    • The configuration log.cleaner.enable is deprecated. Users should no longer set it to false to prepare for future removal. After the removal, log.cleaner.threads will also have a lower bound of 1. For further details, please refer to KIP-1148.
    • The KIP-966 part 1: Eligible Leader Replicas(ELR) will be enabled by default on the new clusters. After the ELR feature enabled, the previously set min.insync.replicas value at the broker-level config will be removed. Please set at the cluster-level if necessary. For further details, please refer to here.
  • Producer
    • The flush method now detects potential deadlocks and prohibits its use inside a callback. This change prevents unintended blocking behavior, which was a known risk in earlier versions.
  • Command
    • The force option of ConfigCommand has been removed, as it has been non-operational since version 0.10.1.0.
  • Admin
    • The listConsumerGroups() and listConsumerGroups(ListConsumerGroupsOptions) methods in Admin are deprecated, and will be removed in the next major version. Use Admin.listGroups(ListGroupsOptions.forConsumerGroups()) instead.
  • Kafka Streams
    • The window.size.ms and window.inner.serde.class in StreamsConfig are deprecated. Use the corresponding string constants defined in TimeWindowedSerializer, TimeWindowedDeserializer, SessionWindowedSerializer and SessionWindowedDeserializer instead.

Upgrading to 4.0.1

Upgrading Clients to 4.0.1

For a rolling upgrade:

  1. Upgrade the clients one at a time: shut down the client, update the code, and restart it.
  2. Clients (including Streams and Connect) must be on version 2.1 or higher before upgrading to 4.0. Many deprecated APIs were removed in Kafka 4.0. For more information about the compatibility, please refer to the compatibility matrix or KIP-1124.

Upgrading Servers to 4.0.1 from any version 3.3.x through 3.9.x

Note: Apache Kafka 4.0 only supports KRaft mode - ZooKeeper mode has been removed. As such, broker upgrades to 4.0.0 (and higher) require KRaft mode and the software and metadata versions must be at least 3.3.x (the first version when KRaft mode was deemed production ready). For clusters in KRaft mode with versions older than 3.3.x, we recommend upgrading to 3.9.x before upgrading to 4.0.x. Clusters in ZooKeeper mode have to be migrated to KRaft mode before they can be upgraded to 4.0.x.

For a rolling upgrade:

  1. Upgrade the brokers one at a time: shut down the broker, update the code, and restart it. Once you have done so, the brokers will be running the latest version and you can verify that the cluster’s behavior and performance meet expectations.
  2. Once the cluster’s behavior and performance have been verified, finalize the upgrade by running bin/kafka-features.sh --bootstrap-server localhost:9092 upgrade --release-version 4.0
  3. Note that cluster metadata downgrade is not supported in this version since it has metadata changes. Every MetadataVersion has a boolean parameter that indicates if there are metadata changes (i.e. IBP_4_0_IV1(23, "4.0", "IV1", true) means this version has metadata changes). Given your current and target versions, a downgrade is only possible if there are no metadata changes in the versions between.

Notable changes in 4.0.1

  • The filename for rotated state-change.log files has been updated from stage-change.log.[date] to state-change.log.[date] in the log4j2.yaml configuration file. See KAFKA-19576 for details.
  • Kafka Streams include a critical fix to upgrade from KStreams#transformValues() (remove with 4.0.0 release) to KStreams#processValues(). For more details, see the migration guide.

Notable changes in 4.0.0

  • Old protocol API versions have been removed. Users should ensure brokers are version 2.1 or higher before upgrading Java clients (including Connect and Kafka Streams which use the clients internally) to 4.0. Similarly, users should ensure their Java clients (including Connect and Kafka Streams) version is 2.1 or higher before upgrading brokers to 4.0. Finally, care also needs to be taken when it comes to kafka clients that are not part of Apache Kafka, please see KIP-896 for the details.
  • Apache Kafka 4.0 only supports KRaft mode - ZooKeeper mode has been removed. About version upgrade, check Upgrading to 4.0.1 from any version 3.3.x through 3.9.x for more info.
  • Apache Kafka 4.0 ships with a brand-new group coordinator implementation (See here). Functionally speaking, it implements all the same APIs. There are reasonable defaults, but the behavior of the new group coordinator can be tuned by setting the configurations with prefix group.coordinator.
  • The Next Generation of the Consumer Rebalance Protocol (KIP-848) is now Generally Available (GA) in Apache Kafka 4.0. The protocol is automatically enabled on the server when the upgrade to 4.0 is finalized. Note that once the new protocol is used by consumer groups, the cluster can only be downgraded to version 3.4.1 or newer. For more information check here.
  • Transactions Server-Side Defense (KIP-890) brings a strengthened transactional protocol to Apache Kafka 4.0. The new and improved transactional protocol is enabled when the upgrade to 4.0 is finalized. When using 4.0 producer clients, the producer epoch is bumped on every transaction to ensure every transaction includes the intended messages and duplicates are not written as part of the next transaction. Downgrading the protocol is safe. For more information check here.
  • Eligible Leader Replicas (KIP-966 Part 1) enhances the replication protocol for the Apache Kafka 4.0. Now the KRaft controller keeps track of the data partition replicas that are not included in ISR but are safe to be elected as leader without data loss. Such replicas are stored in the partition metadata as the Eligible Leader Replicas(ELR). For more information check here.
  • Since Apache Kafka 4.0.0, we have added a system property (org.apache.kafka.sasl.oauthbearer.allowed.urls) to set the allowed URLs as SASL OAUTHBEARER token or jwks endpoints. By default, the value is an empty list. Users should explicitly set the allowed list if necessary.
  • A number of deprecated classes, methods, configurations and tools have been removed.
    • Common
      • The metrics.jmx.blacklist and metrics.jmx.whitelist configurations were removed from the org.apache.kafka.common.metrics.JmxReporter Please use metrics.jmx.exclude and metrics.jmx.include respectively instead.
      • The auto.include.jmx.reporter configuration was removed. The metric.reporters configuration is now set to org.apache.kafka.common.metrics.JmxReporter by default.
      • The constructor org.apache.kafka.common.metrics.JmxReporter with string argument was removed. See KIP-606 for details.
      • The bufferpool-wait-time-total, io-waittime-total, and iotime-total metrics were removed. Please use bufferpool-wait-time-ns-total, io-wait-time-ns-total, and io-time-ns-total metrics as replacements, respectively.
      • The kafka.common.requests.DescribeLogDirsResponse.LogDirInfo class was removed. Please use the kafka.clients.admin.DescribeLogDirsResult.descriptions() class and kafka.clients.admin.DescribeLogDirsResult.allDescriptions() instead.
      • The kafka.common.requests.DescribeLogDirsResponse.ReplicaInfo class was removed. Please use the kafka.clients.admin.DescribeLogDirsResult.descriptions() class and kafka.clients.admin.DescribeLogDirsResult.allDescriptions() instead.
      • The org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerLoginCallbackHandler class was removed. Please use the org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginCallbackHandler class instead.
      • The org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerValidatorCallbackHandler class was removed. Please use the org.apache.kafka.common.security.oauthbearer.OAuthBearerValidatorCallbackHandler class instead.
      • The org.apache.kafka.common.errors.NotLeaderForPartitionException class was removed. The org.apache.kafka.common.errors.NotLeaderOrFollowerException is returned if a request could not be processed because the broker is not the leader or follower for a topic partition.
      • The org.apache.kafka.clients.producer.internals.DefaultPartitioner and org.apache.kafka.clients.producer.UniformStickyPartitioner classes were removed.
      • The log.message.format.version and message.format.version configs were removed.
      • The function onNewBatch in org.apache.kafka.clients.producer.Partitioner class was removed.
      • The default properties files for KRaft mode are no longer stored in the separate config/kraft directory since Zookeeper has been removed. These files have been consolidated with other configuration files. Now all configuration files are in config directory.
      • The valid format for --bootstrap-server only supports comma-separated value, such as host1:port1,host2:port2,.... Providing other formats, like space-separated bootstrap servers (e.g., host1:port1 host2:port2 host3:port3), will result in an exception, even though this was allowed in Apache Kafka versions prior to 4.0.
    • Broker
      • The delegation.token.master.key configuration was removed. Please use delegation.token.secret.key instead.
      • The offsets.commit.required.acks configuration was removed. See KIP-1041 for details.
      • The log.message.timestamp.difference.max.ms configuration was removed. Please use log.message.timestamp.before.max.ms and log.message.timestamp.after.max.ms instead. See KIP-937 for details.
      • The remote.log.manager.copier.thread.pool.size configuration default value was changed to 10 from -1. Values of -1 are no longer valid; a minimum value of 1 or higher is required. See KIP-1030
      • The remote.log.manager.expiration.thread.pool.size configuration default value was changed to 10 from -1. Values of -1 are no longer valid; a minimum value of 1 or higher is required. See KIP-1030
      • The remote.log.manager.thread.pool.size configuration default value was changed to 2 from 10. See KIP-1030
      • The minimum segment.bytes/log.segment.bytes has changed from 14 bytes to 1MB. See KIP-1030
    • MirrorMaker
      • The original MirrorMaker (MM1) and related classes were removed. Please use the Connect-based MirrorMaker (MM2), as described in the Geo-Replication section..
      • The use.incremental.alter.configs configuration was removed from MirrorSourceConnector. The modified behavior is now identical to the previous required configuration, therefore users should ensure that brokers in the target cluster are at least running 2.3.0.
      • The add.source.alias.to.metrics configuration was removed from MirrorSourceConnector. The source cluster alias is now always added to the metrics.
      • The config.properties.blacklist was removed from the org.apache.kafka.connect.mirror.MirrorSourceConfig Please use config.properties.exclude instead.
      • The topics.blacklist was removed from the org.apache.kafka.connect.mirror.MirrorSourceConfig Please use topics.exclude instead.
      • The groups.blacklist was removed from the org.apache.kafka.connect.mirror.MirrorSourceConfig Please use groups.exclude instead.
    • Tools
      • The kafka.common.MessageReader class was removed. Please use the org.apache.kafka.tools.api.RecordReader interface to build custom readers for the kafka-console-producer tool.
      • The kafka.tools.DefaultMessageFormatter class was removed. Please use the org.apache.kafka.tools.consumer.DefaultMessageFormatter class instead.
      • The kafka.tools.LoggingMessageFormatter class was removed. Please use the org.apache.kafka.tools.consumer.LoggingMessageFormatter class instead.
      • The kafka.tools.NoOpMessageFormatter class was removed. Please use the org.apache.kafka.tools.consumer.NoOpMessageFormatter class instead.
      • The --whitelist option was removed from the kafka-console-consumer command line tool. Please use --include instead.
      • Redirections from the old tools packages have been removed: kafka.admin.FeatureCommand, kafka.tools.ClusterTool, kafka.tools.EndToEndLatency, kafka.tools.StateChangeLogMerger, kafka.tools.StreamsResetter, kafka.tools.JmxTool.
      • The --authorizer, --authorizer-properties, and --zk-tls-config-file options were removed from the kafka-acls command line tool. Please use --bootstrap-server or --bootstrap-controller instead.
      • The kafka.serializer.Decoder trait was removed, please use the org.apache.kafka.tools.api.Decoder interface to build custom decoders for the kafka-dump-log tool.
      • The kafka.coordinator.group.OffsetsMessageFormatter class was removed. Please use the org.apache.kafka.tools.consumer.OffsetsMessageFormatter class instead.
      • The kafka.coordinator.group.GroupMetadataMessageFormatter class was removed. Please use the org.apache.kafka.tools.consumer.GroupMetadataMessageFormatter class instead.
      • The kafka.coordinator.transaction.TransactionLogMessageFormatter class was removed. Please use the org.apache.kafka.tools.consumer.TransactionLogMessageFormatter class instead.
      • The --topic-white-list option was removed from the kafka-replica-verification command line tool. Please use --topics-include instead.
      • The --broker-list option was removed from the kafka-verifiable-consumer command line tool. Please use --bootstrap-server instead.
      • kafka-configs.sh now uses incrementalAlterConfigs API to alter broker configurations instead of the deprecated alterConfigs API, and it will fall directly if the broker doesn’t support incrementalAlterConfigs API, which means the broker version is prior to 2.3.x. See KIP-1011 for more details.
      • The kafka.admin.ZkSecurityMigrator tool was removed.
    • Connect
      • The whitelist and blacklist configurations were removed from the org.apache.kafka.connect.transforms.ReplaceField transformation. Please use include and exclude respectively instead.
      • The onPartitionsRevoked(Collection<TopicPartition>) and onPartitionsAssigned(Collection<TopicPartition>) methods were removed from SinkTask.
      • The commitRecord(SourceRecord) method was removed from SourceTask.
    • Consumer
      • The poll(long) method was removed from the consumer. Please use poll(Duration) instead. Note that there is a difference in behavior between the two methods. The poll(Duration) method does not block beyond the timeout awaiting partition assignment, whereas the earlier poll(long) method used to wait beyond the timeout.
      • The committed(TopicPartition) and committed(TopicPartition, Duration) methods were removed from the consumer. Please use committed(Set<TopicPartition>) and committed(Set<TopicPartition>, Duration) instead.
      • The setException(KafkaException) method was removed from the org.apache.kafka.clients.consumer.MockConsumer. Please use setPollException(KafkaException) instead.
    • Producer
      • The enable.idempotence configuration will no longer automatically fall back when the max.in.flight.requests.per.connection value exceeds 5.
      • The deprecated sendOffsetsToTransaction(Map<TopicPartition, OffsetAndMetadata>, String) method has been removed from the Producer API.
      • The default linger.ms changed from 0 to 5 in Apache Kafka 4.0 as the efficiency gains from larger batches typically result in similar or lower producer latency despite the increased linger.
    • Admin client
      • The alterConfigs method was removed from the org.apache.kafka.clients.admin.Admin. Please use incrementalAlterConfigs instead.
      • The org.apache.kafka.common.ConsumerGroupState enumeration and related methods have been deprecated. Please use GroupState instead which applies to all types of group.
      • The Admin.describeConsumerGroups method used to return a ConsumerGroupDescription in state DEAD if the group ID was not found. In Apache Kafka 4.0, the GroupIdNotFoundException is thrown instead as part of the support for new types of group.
      • The org.apache.kafka.clients.admin.DeleteTopicsResult.values() method was removed. Please use org.apache.kafka.clients.admin.DeleteTopicsResult.topicNameValues() instead.
      • The org.apache.kafka.clients.admin.TopicListing.TopicListing(String, boolean) method was removed. Please use org.apache.kafka.clients.admin.TopicListing.TopicListing(String, Uuid, boolean) instead.
      • The org.apache.kafka.clients.admin.ListConsumerGroupOffsetsOptions.topicPartitions(List<TopicPartition>) method was removed. Please use org.apache.kafka.clients.admin.Admin.listConsumerGroupOffsets(Map<String, ListConsumerGroupOffsetsSpec>, ListConsumerGroupOffsetsOptions) instead.
      • The deprecated dryRun methods were removed from the org.apache.kafka.clients.admin.UpdateFeaturesOptions. Please use validateOnly instead.
      • The constructor org.apache.kafka.clients.admin.FeatureUpdate with short and boolean arguments was removed. Please use the constructor that accepts short and the specified UpgradeType enum instead.
      • The allowDowngrade method was removed from the org.apache.kafka.clients.admin.FeatureUpdate.
      • The org.apache.kafka.clients.admin.DescribeTopicsResult.DescribeTopicsResult(Map<String, KafkaFuture<TopicDescription>>) method was removed. Please use org.apache.kafka.clients.admin.DescribeTopicsResult.DescribeTopicsResult(Map<Uuid, KafkaFuture<TopicDescription>>, Map<String, KafkaFuture<TopicDescription>>) instead.
      • The values() method was removed from the org.apache.kafka.clients.admin.DescribeTopicsResult. Please use topicNameValues() instead.
      • The all() method was removed from the org.apache.kafka.clients.admin.DescribeTopicsResult. Please use allTopicNames() instead.
    • Kafka Streams
      • All public APIs, deprecated in Apache Kafka 3.6 or an earlier release, have been removed, with the exception of JoinWindows.of() and JoinWindows#grace(). See KAFKA-17531 for details.
      • The most important changes are highlighted in the Kafka Streams upgrade guide.
      • For a full list of changes, see KAFKA-12822.
      • If you are using KStream#transformValues() which was removed with Apache Kafka 4.0.0 release, and you need to rewrite your program to use KStreams#processValues() instead, pay close attention to the migration guide.
  • Other changes:
    • The minimum Java version required by clients and Kafka Streams applications has been increased from Java 8 to Java 11 while brokers, connect and tools now require Java 17. See KIP-750 and KIP-1013 for more details.
    • Java 23 support has been added in Apache Kafka 4.0.
    • Scala 2.12 support has been removed in Apache Kafka 4.0. See KIP-751 for more details
    • Logging framework has been migrated from Log4j to Log4j2. Users can use the log4j-transform-cli tool to automatically convert their existing Log4j configuration files to Log4j2 format. See log4j-transform-cli for more details. Log4j2 provides limited compatibility for Log4j configurations. See Use Log4j 1 to Log4j 2 bridge for more information,
    • KafkaLog4jAppender has been removed, users should migrate to the log4j2 appender See KafkaAppender for more details
    • The --delete-config option in the kafka-topics command line tool has been deprecated.
    • For implementors of RemoteLogMetadataManager (RLMM), a new API nextSegmentWithTxnIndex is introduced in RLMM to allow the implementation to return the next segment metadata with a transaction index. This API is used when the consumers are enabled with isolation level as READ_COMMITTED. See KIP-1058 for more details.
    • The criteria for identifying internal topics in ReplicationPolicy and DefaultReplicationPolicy have been updated to enable the replication of topics that appear to be internal but aren’t truly internal to Kafka and Mirror Maker 2. See KIP-1074 for more details.
    • KIP-714 is now enabled for Kafka Streams via KIP-1076. This allows to not only collect the metric of the internally used clients of a Kafka Streams application via a broker-side plugin, but also to collect the metrics of the Kafka Streams runtime itself.
    • The default value of num.recovery.threads.per.data.dir has been changed from 1 to 2. The impact of this is faster recovery post unclean shutdown at the expense of extra IO cycles. See KIP-1030
    • The default value of message.timestamp.after.max.ms has been changed from Long.Max to 1 hour. The impact of this messages with a timestamp of more than 1 hour in the future will be rejected when message.timestamp.type=CreateTime is set. See KIP-1030
    • Introduced in KIP-890, the TransactionAbortableException enhances error handling within transactional operations by clearly indicating scenarios where transactions should be aborted due to errors. It is important for applications to properly manage both TimeoutException and TransactionAbortableException when working with transaction producers.
      • TimeoutException: This exception indicates that a transactional operation has timed out. Given the risk of message duplication that can arise from retrying operations after a timeout (potentially violating exactly-once semantics), applications should treat timeouts as reasons to abort the ongoing transaction.
      • TransactionAbortableException: Specifically introduced to signal errors that should lead to transaction abortion, ensuring this exception is properly handled is critical for maintaining the integrity of transactional processing.
      • To ensure seamless operation and compatibility with future Kafka versions, developers are encouraged to update their error-handling logic to treat both exceptions as triggers for aborting transactions. This approach is pivotal for preserving exactly-once semantics.
      • See KIP-890 and KIP-1050 for more details
    • The filename for rotated state-change.log files incorrectly rotates to stage-change.log.[date] (changing state to stage). This issue is corrected in 4.0.1. See KAFKA-19576 for details.

Upgrading to 3.9.0 and older versions

See Upgrading From Previous Versions in the 3.9 documentation.

Last modified February 16, 2026: Add 4.2 documentation and javadocs (#785) (956020beb)