Kafka Streams Configuration Reference for Confluent Platform

This topic provides configuration parameters available for Confluent Platform. The Kafka Streams parameters are organized by order of importance, ranked from high to low.

application.id

An identifier for the stream processing application. Must be unique within the Kafka cluster. It is used as 1) the default client-id prefix, 2) the group-id for membership management, 3) the changelog topic prefix.

Type:	string
Default:
Valid Values:
Importance:	high

bootstrap.servers

A list of host/port pairs used to establish the initial connection to the Kafka cluster. Clients use this list to bootstrap and discover the full set of Kafka brokers. While the order of servers in the list does not matter, we recommend including more than one server to ensure resilience if any servers are down. This list does not need to contain the entire set of brokers, as Kafka clients automatically manage and update connections to the cluster efficiently. This list must be in the form host1:port1,host2:port2,....

Type:	list
Default:
Valid Values:	[] (empty not allowed) (null not allowed)
Importance:	high

ensure.explicit.internal.resource.naming

Whether to enforce explicit naming for all internal resources of the topology, including internal topics (e.g., changelog and repartition topics) and their associated state stores. When enabled, the application will refuse to start if any internal resource has an auto-generated name.

Type:	boolean
Default:	false
Valid Values:
Importance:	high

num.standby.replicas

The number of standby replicas for each task.

Type:	int
Default:	0
Valid Values:
Importance:	high

state.dir

Directory location for state store. This path must be unique for each streams instance sharing the same underlying filesystem. Note that if not configured, then the default location will be different in each environment as it is computed using System.getProperty(“java.io.tmpdir”)

Type:	string
Default:	${java.io.tmpdir}
Valid Values:
Importance:	high

acceptable.recovery.lag

The maximum acceptable lag (number of offsets to catch up) for a client to be considered caught-up enough to receive an active task assignment. Upon assignment, it will still restore the rest of the changelog before processing. To avoid a pause in processing during rebalances, this config should correspond to a recovery time of well under a minute for a given workload. Must be at least 0.

Type:	long
Default:	10000
Valid Values:	[0,…]
Importance:	medium

cache.max.bytes.buffering

Maximum number of memory bytes to be used for buffering across all threads

Type:	long
Default:	10485760
Valid Values:	[0,…]
Importance:	medium

client.id

An ID prefix string used for the client IDs of internal (main, restore, and global) consumers , producers, and admin clients with pattern -[Global]StreamThread[-]-<consumer|producer|restore-consumer|global-consumer>.

Type:	string
Default:	-
Valid Values:
Importance:	medium

default.deserialization.exception.handler

Exception handling class that implements the org.apache.kafka.streams.errors.DeserializationExceptionHandler interface.

Type:	class
Default:	org.apache.kafka.streams.errors.LogAndFailExceptionHandler
Valid Values:
Importance:	medium

default.key.serde

Default serializer / deserializer class for key that implements the org.apache.kafka.common.serialization.Serde interface.

Type:	class
Default:	null
Valid Values:
Importance:	medium

default.list.key.serde.inner

Default inner class of list serde for key that implements the org.apache.kafka.common.serialization.Serde interface. This configuration will be read if and only if default.key.serde configuration is set to org.apache.kafka.common.serialization.Serdes.ListSerde

Type:	class
Default:	null
Valid Values:
Importance:	medium

default.list.key.serde.type

Default class for key that implements the java.util.List interface. This configuration will be read if and only if default.key.serde configuration is set to org.apache.kafka.common.serialization.Serdes.ListSerde Note when list serde class is used, one needs to set the inner serde class that implements the org.apache.kafka.common.serialization.Serde interface via ‘default.list.key.serde.inner’

Type:	class
Default:	null
Valid Values:
Importance:	medium

default.list.value.serde.inner

Default inner class of list serde for value that implements the org.apache.kafka.common.serialization.Serde interface. This configuration will be read if and only if default.value.serde configuration is set to org.apache.kafka.common.serialization.Serdes.ListSerde

Type:	class
Default:	null
Valid Values:
Importance:	medium

default.list.value.serde.type

Default class for value that implements the java.util.List interface. This configuration will be read if and only if default.value.serde configuration is set to org.apache.kafka.common.serialization.Serdes.ListSerde Note when list serde class is used, one needs to set the inner serde class that implements the org.apache.kafka.common.serialization.Serde interface via ‘default.list.value.serde.inner’

Type:	class
Default:	null
Valid Values:
Importance:	medium

default.production.exception.handler

Exception handling class that implements the org.apache.kafka.streams.errors.ProductionExceptionHandler interface.

Type:	class
Default:	org.apache.kafka.streams.errors.DefaultProductionExceptionHandler
Valid Values:
Importance:	medium

default.timestamp.extractor

Default timestamp extractor class that implements the org.apache.kafka.streams.processor.TimestampExtractor interface.

Type:	class
Default:	org.apache.kafka.streams.processor.FailOnInvalidTimestamp
Valid Values:
Importance:	medium

default.value.serde

Default serializer / deserializer class for value that implements the org.apache.kafka.common.serialization.Serde interface.

Type:	class
Default:	null
Valid Values:
Importance:	medium

deserialization.exception.handler

Exception handling class that implements the org.apache.kafka.streams.errors.DeserializationExceptionHandler interface.

Type:	class
Default:	org.apache.kafka.streams.errors.LogAndFailExceptionHandler
Valid Values:
Importance:	medium

errors.dead.letter.queue.topic.name

If not null, the default exception handler will build and send a Dead Letter Queue record to the topic with the provided name if an error occurs.If a custom deserialization/production or processing exception handler is set, this parameter is ignored for this handler.

Type:	string
Default:	null
Valid Values:
Importance:	medium

group.protocol

The group protocol streams should use. We currently support “classic” or “streams”. If “streams” is specified, then the streams rebalance protocol will be used. Otherwise, the classic group protocol will be used.

Type:	string
Default:	classic
Valid Values:	(case insensitive) [STREAMS, CLASSIC]
Importance:	medium

max.task.idle.ms

This config controls whether joins and merges may produce out-of-order results. The config value is the maximum amount of time in milliseconds a stream task will stay idle when it is fully caught up on some (but not all) input partitions to wait for producers to send additional records and avoid potential out-of-order record processing across multiple input streams. The default (zero) does not wait for producers to send more records, but it does wait to fetch data that is already present on the brokers. This default means that for records that are already present on the brokers, Streams will process them in timestamp order. Set to -1 to disable idling entirely and process any locally available data, even though doing so may produce out-of-order processing.

Type:	long
Default:	0
Valid Values:
Importance:	medium

max.warmup.replicas

The maximum number of warmup replicas (extra standbys beyond the configured num.standbys) that can be assigned at once for the purpose of keeping the task available on one instance while it is warming up on another instance it has been reassigned to. Used to throttle how much extra broker traffic and cluster state can be used for high availability. Must be at least 1.Note that one warmup replica corresponds to one Stream Task. Furthermore, note that each warmup replica can only be promoted to an active task during a rebalance (normally during a so-called probing rebalance, which occur at a frequency specified by the probing.rebalance.interval.ms config). This means that the maximum rate at which active tasks can be migrated from one Kafka Streams Instance to another instance can be determined by (max.warmup.replicas / probing.rebalance.interval.ms).

Type:	int
Default:	2
Valid Values:	[1,…]
Importance:	medium

num.stream.threads

The number of threads to execute stream processing.

Type:	int
Default:	1
Valid Values:
Importance:	medium

processing.exception.handler

Exception handling class that implements the org.apache.kafka.streams.errors.ProcessingExceptionHandler interface.

Type:	class
Default:	org.apache.kafka.streams.errors.LogAndFailProcessingExceptionHandler
Valid Values:
Importance:	medium

processing.guarantee

The processing guarantee that should be used. Possible values are at_least_once (default) and exactly_once_v2 (requires brokers version 2.5 or higher). Note that exactly-once processing requires a cluster of at least three brokers by default what is the recommended setting for production; for development you can change this, by adjusting broker setting transaction.state.log.replication.factor and transaction.state.log.min.isr.

Type:	string
Default:	at_least_once
Valid Values:	[at_least_once, exactly_once_v2]
Importance:	medium

production.exception.handler

Exception handling class that implements the org.apache.kafka.streams.errors.ProductionExceptionHandler interface.

Type:	class
Default:	org.apache.kafka.streams.errors.DefaultProductionExceptionHandler
Valid Values:
Importance:	medium

replication.factor

The replication factor for change log topics and repartition topics created by the stream processing application. The default of -1 (meaning: use broker default replication factor) requires broker version 2.4 or newer

Type:	int
Default:	-1
Valid Values:
Importance:	medium

security.protocol

Protocol used to communicate with brokers.

Type:	string
Default:	PLAINTEXT
Valid Values:	(case insensitive) [SASL_SSL, PLAINTEXT, SSL, SASL_PLAINTEXT]
Importance:	medium

statestore.cache.max.bytes

Maximum number of memory bytes to be used for statestore cache across all threads

Type:	long
Default:	10485760 (10 mebibytes)
Valid Values:	[0,…]
Importance:	medium

task.assignor.class

A task assignor class or class name implementing the org.apache.kafka.streams.processor.assignment.TaskAssignor interface. Defaults to the HighAvailabilityTaskAssignor class.

Type:	string
Default:	null
Valid Values:
Importance:	medium

task.timeout.ms

The maximum amount of time in milliseconds a task might stall due to internal errors and retries until an error is raised. For a timeout of 0ms, a task would raise an error for the first internal error. For any timeout larger than 0ms, a task will retry at least once before an error is raised.

Type:	long
Default:	300000 (5 minutes)
Valid Values:	[0,…]
Importance:	medium

topology.optimization

A configuration telling Kafka Streams if it should optimize the topology and what optimizations to apply. Acceptable values are: “+NO_OPTIMIZATION+”, “+OPTIMIZE+”, or a comma separated list of specific optimizations: (“+REUSE_KTABLE_SOURCE_TOPICS+”, “+MERGE_REPARTITION_TOPICS+” + “SINGLE_STORE_SELF_JOIN+”).”NO_OPTIMIZATION” by default.

Type:	string
Default:	none
Valid Values:	[all, none, reuse.ktable.source.topics, merge.repartition.topics, single.store.self.join]
Importance:	medium

allow.os.group.write.access

Allows state store directories created by Kafka Streams to have write access for the OS group. Default is false

Type:	boolean
Default:	false
Valid Values:
Importance:	low

application.server

A host:port pair pointing to a user-defined endpoint that can be used for state store discovery and interactive queries on this KafkaStreams instance.

Type:	string
Default:	“”
Valid Values:
Importance:	low

buffered.records.per.partition

Maximum number of records to buffer per partition.

Type:	int
Default:	1000
Valid Values:
Importance:	low

built.in.metrics.version

Version of the built-in metrics to use.

Type:	string
Default:	latest
Valid Values:	[latest]
Importance:	low

commit.interval.ms

The frequency in milliseconds with which to commit processing progress. For at-least-once processing, committing means to save the position (ie, offsets) of the processor. For exactly-once processing, it means to commit the transaction which includes to save the position and to make the committed data in the output topic visible to consumers with isolation level read_committed. (Note, if processing.guarantee is set to exactly_once_v2, the default value is 100, otherwise the default value is 30000.

Type:	long
Default:	30000 (30 seconds)
Valid Values:	[0,…]
Importance:	low

config.providers

Comma-separated alias names for classes implementing the ConfigProvider interface. This enables loading configuration data (such as passwords, API keys, and other credentials) from external sources. For example, see Configuration Providers.

Type:	list
Default:	“”
Valid Values:	[] (empty config allowed) (null not allowed)
Importance:	low

connections.max.idle.ms

Close idle connections after the number of milliseconds specified by this config.

Type:	long
Default:	540000 (9 minutes)
Valid Values:
Importance:	low

default.client.supplier

Client supplier class that implements the org.apache.kafka.streams.KafkaClientSupplier interface.

Type:	class
Default:	org.apache.kafka.streams.processor.internals.DefaultKafkaClientSupplier
Valid Values:
Importance:	low

default.dsl.store

The default state store type used by DSL operators.

Type:	string
Default:	rocksDB
Valid Values:	[rocksDB, in_memory]
Importance:	low

dsl.store.suppliers.class

Defines which store implementations to plug in to DSL operators. Must implement the org.apache.kafka.streams.state.DslStoreSuppliers interface.

Type:	class
Default:	org.apache.kafka.streams.state.BuiltInDslStoreSuppliers$RocksDBDslStoreSuppliers
Valid Values:
Importance:	low

enable.metrics.push

Whether to enable pushing of internal client metrics for (main, restore, and global) consumers, producers, and admin clients. The cluster must have a client metrics subscription which corresponds to a client.

Type:	boolean
Default:	true
Valid Values:
Importance:	low

log.summary.interval.ms

The output interval in milliseconds for logging summary information.If greater or equal to 0, the summary log will be output according to the set time interval;If less than 0, summary output is disabled.

Type:	long
Default:	120000 (2 minutes)
Valid Values:
Importance:	low

metadata.max.age.ms

The period of time in milliseconds after which we force a refresh of metadata even if we haven’t seen any partition leadership changes to proactively discover any new brokers or partitions.

Type:	long
Default:	300000 (5 minutes)
Valid Values:	[0,…]
Importance:	low

metadata.recovery.rebootstrap.trigger.ms

If a client configured to rebootstrap using metadata.recovery.strategy=rebootstrap is unable to obtain metadata from any of the brokers in the last known metadata for this interval, client repeats the bootstrap process using bootstrap.servers configuration.

Type:	long
Default:	300000 (5 minutes)
Valid Values:	[0,…]
Importance:	low

metadata.recovery.strategy

Controls how the client recovers when none of the brokers known to it is available. If set to none, the client fails. If set to rebootstrap, the client repeats the bootstrap process using bootstrap.servers. Rebootstrapping is useful when a client communicates with brokers so infrequently that the set of brokers may change entirely before the client refreshes metadata. Metadata recovery is triggered when all last-known brokers appear unavailable simultaneously. Brokers appear unavailable when disconnected and no current retry attempt is in-progress. Consider increasing reconnect.backoff.ms and reconnect.backoff.max.ms and decreasing socket.connection.setup.timeout.ms and socket.connection.setup.timeout.max.ms for the client. Rebootstrap is also triggered if connection cannot be established to any of the brokers for metadata.recovery.rebootstrap.trigger.ms milliseconds or if server requests rebootstrap.

Type:	string
Default:	rebootstrap
Valid Values:	(case insensitive) [REBOOTSTRAP, NONE]
Importance:	low

metric.reporters

A list of classes to use as metrics reporters. Implementing the org.apache.kafka.common.metrics.MetricsReporter interface allows plugging in classes that will be notified of new metric creation. When custom reporters are set and org.apache.kafka.common.metrics.JmxReporter is needed, it has to be explicitly added to the list.

Type:	list
Default:	org.apache.kafka.common.metrics.JmxReporter
Valid Values:	[] (empty config allowed) (null not allowed)
Importance:	low

metrics.num.samples

The number of samples maintained to compute metrics.

Type:	int
Default:	2
Valid Values:	[1,…]
Importance:	low

metrics.recording.level

The highest recording level for metrics. It has three levels for recording metrics - info, debug, and trace. INFO level records only essential metrics necessary for monitoring system performance and health. It collects vital data without gathering too much detail, making it suitable for production environments where minimal overhead is desired.DEBUG level records most metrics, providing more detailed information about the system’s operation. It’s useful for development and testing environments where you need deeper insights to debug and fine-tune the application.TRACE level records all possible metrics, capturing every detail about the system’s performance and operation. It’s best for controlled environments where in-depth analysis is required, though it can introduce significant overhead.

Type:	string
Default:	INFO
Valid Values:	[INFO, DEBUG, TRACE]
Importance:	low

metrics.sample.window.ms

The window of time a metrics sample is computed over.

Type:	long
Default:	30000 (30 seconds)
Valid Values:	[0,…]
Importance:	low

poll.ms

The amount of time in milliseconds to block waiting for input.

Type:	long
Default:	100
Valid Values:
Importance:	low

probing.rebalance.interval.ms

The maximum time in milliseconds to wait before triggering a rebalance to probe for warmup replicas that have finished warming up and are ready to become active. Probing rebalances will continue to be triggered until the assignment is balanced. Must be at least 1 minute.

Type:	long
Default:	600000 (10 minutes)
Valid Values:	[60000,…]
Importance:	low

processor.wrapper.class

A processor wrapper class or class name that implements the org.apache.kafka.streams.state.ProcessorWrapper interface. Must be passed in to the StreamsBuilder or Topology constructor in order to take effect

Type:	class
Default:	org.apache.kafka.streams.processor.internals.NoOpProcessorWrapper
Valid Values:
Importance:	low

rack.aware.assignment.non_overlap_cost

Cost associated with moving tasks from existing assignment. This config and rack.aware.assignment.traffic_cost controls whether the optimization algorithm favors minimizing cross rack traffic or minimize the movement of tasks in existing assignment. If set a larger value org.apache.kafka.streams.processor.internals.assignment.RackAwareTaskAssignor will optimize to maintain the existing assignment. The default value is null which means it will use default non_overlap cost values in different assignors.

Type:	int
Default:	null
Valid Values:
Importance:	low

rack.aware.assignment.strategy

The strategy we use for rack aware assignment. Rack aware assignment will take client.rack and racks of TopicPartition into account when assigning tasks to minimize cross rack traffic. Valid settings are : none (default), which will disable rack aware assignment; min_traffic, which will compute minimum cross rack traffic assignment; balance_subtopology, which will compute minimum cross rack traffic and try to balance the tasks of same subtopologies across different clients

Type:	string
Default:	none
Valid Values:	[none, min_traffic, balance_subtopology]
Importance:	low

rack.aware.assignment.tags

List of client tag keys used to distribute standby replicas across Kafka Streams instances. When configured, Kafka Streams will make a best-effort to distribute the standby tasks over each client tag dimension.

Type:	list
Default:	“”
Valid Values:	List containing maximum of 5 elements
Importance:	low

rack.aware.assignment.traffic_cost

Cost associated with cross rack traffic. This config and rack.aware.assignment.non_overlap_cost controls whether the optimization algorithm favors minimizing cross rack traffic or minimize the movement of tasks in existing assignment. If set a larger value org.apache.kafka.streams.processor.internals.assignment.RackAwareTaskAssignor will optimize for minimizing cross rack traffic. The default value is null which means it will use default traffic cost values in different assignors.

Type:	int
Default:	null
Valid Values:
Importance:	low

receive.buffer.bytes

The size of the TCP receive buffer (SO_RCVBUF) to use when reading data. If the value is -1, the OS default will be used.

Type:	int
Default:	32768 (32 kibibytes)
Valid Values:	[-1,…]
Importance:	low

reconnect.backoff.max.ms

The maximum amount of time in milliseconds to wait when reconnecting to a broker that has repeatedly failed to connect. If provided, the backoff per host will increase exponentially for each consecutive connection failure, up to this maximum. After calculating the backoff increase, 20% random jitter is added to avoid connection storms.

Type:	long
Default:	1000 (1 second)
Valid Values:	[0,…]
Importance:	low

reconnect.backoff.ms

The base amount of time to wait before attempting to reconnect to a given host. This avoids repeatedly connecting to a host in a tight loop. This backoff applies to all connection attempts by the client to a broker. This value is the initial backoff value and will increase exponentially for each consecutive connection failure, up to the reconnect.backoff.max.ms value.

Type:	long
Default:	50
Valid Values:	[0,…]
Importance:	low

repartition.purge.interval.ms

The frequency in milliseconds with which to delete fully consumed records from repartition topics. Purging will occur after at least this value since the last purge, but may be delayed until later. (Note, unlike commit.interval.ms, the default for this value remains unchanged when processing.guarantee is set to exactly_once_v2).

Type:	long
Default:	30000 (30 seconds)
Valid Values:	[0,…]
Importance:	low

request.timeout.ms

The configuration controls the maximum amount of time the client will wait for the response of a request. If the response is not received before the timeout elapses the client will resend the request if necessary or fail the request if retries are exhausted.

Type:	int
Default:	40000 (40 seconds)
Valid Values:	[0,…]
Importance:	low

retry.backoff.ms

The amount of time to wait before attempting to retry a failed request to a given topic partition. This avoids repeatedly sending requests in a tight loop under some failure scenarios. This value is the initial backoff value and will increase exponentially for each failed request, up to the retry.backoff.max.ms value.

Type:	long
Default:	100
Valid Values:	[0,…]
Importance:	low

rocksdb.config.setter

A Rocks DB config setter class or class name that implements the org.apache.kafka.streams.state.RocksDBConfigSetter interface

Type:	class
Default:	null
Valid Values:
Importance:	low

send.buffer.bytes

The size of the TCP send buffer (SO_SNDBUF) to use when sending data. If the value is -1, the OS default will be used.

Type:	int
Default:	131072 (128 kibibytes)
Valid Values:	[-1,…]
Importance:	low

state.cleanup.delay.ms

The amount of time in milliseconds to wait before deleting state when a partition has migrated. Only state directories that have not been modified for at least state.cleanup.delay.ms will be removed

Type:	long
Default:	600000 (10 minutes)
Valid Values:
Importance:	low

upgrade.from

Allows live upgrading (and downgrading in some cases – see upgrade guide) in a backward compatible way. Default is null. Please refer to the Kafka Streams upgrade guide for instructions on how and when to use this config. Note that when upgrading from 3.5 to a newer version it is never required to specify this config, while upgrading live directly to 4.0+ from 2.3 or below is no longer supported even with this config.

Type:	string
Default:	null
Valid Values:	[null, 2.4, 2.5, 2.6, 2.7, 2.8, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1]
Importance:	low

window.size.ms

Sets window size for the deserializer in order to calculate window end times.

Type:	long
Default:	null
Valid Values:
Importance:	low

windowed.inner.class.serde

Default serializer / deserializer for the inner class of a windowed record. Must implement the org.apache.kafka.common.serialization.Serde interface. Note that setting this config in KafkaStreams application would result in an error as it is meant to be used only from Plain consumer client.

Type:	string
Default:	null
Valid Values:
Importance:	low

windowstore.changelog.additional.retention.ms

Added to a windows maintainMs to ensure data is not deleted from the log prematurely. Allows for clock drift. Default is 1 day

Type:	long
Default:	86400000 (1 day)
Valid Values:
Importance:	low

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