Chapter 190. Kafka Component

Available as of Camel version 2.13

The kafka: component is used for communicating with Apache Kafka message broker.

Maven users will need to add the following dependency to their pom.xml for this component.

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-kafka</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

190.1. URI format

kafka:topic[?options]

190.2. Options

The Kafka component supports 8 options, which are listed below.

Name	Description	Default	Type
configuration (common)	Allows to pre-configure the Kafka component with common options that the endpoints will reuse.		KafkaConfiguration
brokers (common)	URL of the Kafka brokers to use. The format is host1:port1,host2:port2, and the list can be a subset of brokers or a VIP pointing to a subset of brokers. This option is known as bootstrap.servers in the Kafka documentation.		String
workerPool (advanced)	To use a shared custom worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing. If using this option then you must handle the lifecycle of the thread pool to shut the pool down when no longer needed.		ExecutorService
useGlobalSslContext Parameters (security)	Enable usage of global SSL context parameters.	false	boolean
breakOnFirstError (consumer)	This options controls what happens when a consumer is processing an exchange and it fails. If the option is false then the consumer continues to the next message and processes it. If the option is true then the consumer breaks out, and will seek back to offset of the message that caused a failure, and then re-attempt to process this message. However this can lead to endless processing of the same message if its bound to fail every time, eg a poison message. Therefore its recommended to deal with that for example by using Camel’s error handler.	false	boolean
allowManualCommit (consumer)	Whether to allow doing manual commits via KafkaManualCommit. If this option is enabled then an instance of KafkaManualCommit is stored on the Exchange message header, which allows end users to access this API and perform manual offset commits via the Kafka consumer.	false	boolean
kafkaManualCommit Factory (consumer)	Factory to use for creating KafkaManualCommit instances. This allows to plugin a custom factory to create custom KafkaManualCommit instances in case special logic is needed when doing manual commits that deviates from the default implementation that comes out of the box.		KafkaManualCommit Factory
resolveProperty Placeholders (advanced)	Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.	true	boolean

The Kafka endpoint is configured using URI syntax:

kafka:topic

with the following path and query parameters:

190.2.1. Path Parameters (1 parameters):

Name	Description	Default	Type
topic	Required Name of the topic to use. On the consumer you can use comma to separate multiple topics. A producer can only send a message to a single topic.		String

190.2.2. Query Parameters (93 parameters):

Name	Description	Default	Type
brokers (common)	URL of the Kafka brokers to use. The format is host1:port1,host2:port2, and the list can be a subset of brokers or a VIP pointing to a subset of brokers. This option is known as bootstrap.servers in the Kafka documentation.		String
clientId (common)	The client id is a user-specified string sent in each request to help trace calls. It should logically identify the application making the request.		String
headerFilterStrategy (common)	To use a custom HeaderFilterStrategy to filter header to and from Camel message.		HeaderFilterStrategy
reconnectBackoffMaxMs (common)	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.	1000	Integer
allowManualCommit (consumer)	Whether to allow doing manual commits via KafkaManualCommit. If this option is enabled then an instance of KafkaManualCommit is stored on the Exchange message header, which allows end users to access this API and perform manual offset commits via the Kafka consumer.	false	boolean
autoCommitEnable (consumer)	If true, periodically commit to ZooKeeper the offset of messages already fetched by the consumer. This committed offset will be used when the process fails as the position from which the new consumer will begin.	true	Boolean
autoCommitIntervalMs (consumer)	The frequency in ms that the consumer offsets are committed to zookeeper.	5000	Integer
autoCommitOnStop (consumer)	Whether to perform an explicit auto commit when the consumer stops to ensure the broker has a commit from the last consumed message. This requires the option autoCommitEnable is turned on. The possible values are: sync, async, or none. And sync is the default value.	sync	String
autoOffsetReset (consumer)	What to do when there is no initial offset in ZooKeeper or if an offset is out of range: earliest : automatically reset the offset to the earliest offset latest : automatically reset the offset to the latest offset fail: throw exception to the consumer	latest	String
breakOnFirstError (consumer)	This options controls what happens when a consumer is processing an exchange and it fails. If the option is false then the consumer continues to the next message and processes it. If the option is true then the consumer breaks out, and will seek back to offset of the message that caused a failure, and then re-attempt to process this message. However this can lead to endless processing of the same message if its bound to fail every time, eg a poison message. Therefore its recommended to deal with that for example by using Camel’s error handler.	false	boolean
bridgeErrorHandler (consumer)	Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.	false	boolean
checkCrcs (consumer)	Automatically check the CRC32 of the records consumed. This ensures no on-the-wire or on-disk corruption to the messages occurred. This check adds some overhead, so it may be disabled in cases seeking extreme performance.	true	Boolean
consumerRequestTimeoutMs (consumer)	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.	40000	Integer
consumersCount (consumer)	The number of consumers that connect to kafka server	1	int
consumerStreams (consumer)	Number of concurrent consumers on the consumer	10	int
fetchMaxBytes (consumer)	The maximum amount of data the server should return for a fetch request This is not an absolute maximum, if the first message in the first non-empty partition of the fetch is larger than this value, the message will still be returned to ensure that the consumer can make progress. The maximum message size accepted by the broker is defined via message.max.bytes (broker config) or max.message.bytes (topic config). Note that the consumer performs multiple fetches in parallel.	52428800	Integer
fetchMinBytes (consumer)	The minimum amount of data the server should return for a fetch request. If insufficient data is available the request will wait for that much data to accumulate before answering the request.	1	Integer
fetchWaitMaxMs (consumer)	The maximum amount of time the server will block before answering the fetch request if there isn’t sufficient data to immediately satisfy fetch.min.bytes	500	Integer
groupId (consumer)	A string that uniquely identifies the group of consumer processes to which this consumer belongs. By setting the same group id multiple processes indicate that they are all part of the same consumer group. This option is required for consumers.		String
heartbeatIntervalMs (consumer)	The expected time between heartbeats to the consumer coordinator when using Kafka’s group management facilities. Heartbeats are used to ensure that the consumer’s session stays active and to facilitate rebalancing when new consumers join or leave the group. The value must be set lower than session.timeout.ms, but typically should be set no higher than 1/3 of that value. It can be adjusted even lower to control the expected time for normal rebalances.	3000	Integer
kafkaHeaderDeserializer (consumer)	Sets custom KafkaHeaderDeserializer for deserialization kafka headers values to camel headers values.		KafkaHeaderDeserializer
keyDeserializer (consumer)	Deserializer class for key that implements the Deserializer interface.	org.apache.kafka.common.serialization.StringDeserializer	String
maxPartitionFetchBytes (consumer)	The maximum amount of data per-partition the server will return. The maximum total memory used for a request will be #partitions max.partition.fetch.bytes. This size must be at least as large as the maximum message size the server allows or else it is possible for the producer to send messages larger than the consumer can fetch. If that happens, the consumer can get stuck trying to fetch a large message on a certain partition.	1048576	Integer
maxPollIntervalMs (consumer)	The maximum delay between invocations of poll() when using consumer group management. This places an upper bound on the amount of time that the consumer can be idle before fetching more records. If poll() is not called before expiration of this timeout, then the consumer is considered failed and the group will rebalance in order to reassign the partitions to another member.		Long
maxPollRecords (consumer)	The maximum number of records returned in a single call to poll()	500	Integer
offsetRepository (consumer)	The offset repository to use in order to locally store the offset of each partition of the topic. Defining one will disable the autocommit.		StateRepository
partitionAssignor (consumer)	The class name of the partition assignment strategy that the client will use to distribute partition ownership amongst consumer instances when group management is used	org.apache.kafka.clients.consumer.RangeAssignor	String
pollTimeoutMs (consumer)	The timeout used when polling the KafkaConsumer.	5000	Long
seekTo (consumer)	Set if KafkaConsumer will read from beginning or end on startup: beginning : read from beginning end : read from end This is replacing the earlier property seekToBeginning		String
sessionTimeoutMs (consumer)	The timeout used to detect failures when using Kafka’s group management facilities.	10000	Integer
topicIsPattern (consumer)	Whether the topic is a pattern (regular expression). This can be used to subscribe to dynamic number of topics matching the pattern.	false	boolean
valueDeserializer (consumer)	Deserializer class for value that implements the Deserializer interface.	org.apache.kafka.common.serialization.StringDeserializer	String
exceptionHandler (consumer)	To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored.		ExceptionHandler
exchangePattern (consumer)	Sets the exchange pattern when the consumer creates an exchange.		ExchangePattern
bridgeEndpoint (producer)	If the option is true, then KafkaProducer will ignore the KafkaConstants.TOPIC header setting of the inbound message.	false	boolean
bufferMemorySize (producer)	The total bytes of memory the producer can use to buffer records waiting to be sent to the server. If records are sent faster than they can be delivered to the server the producer will either block or throw an exception based on the preference specified by block.on.buffer.full.This setting should correspond roughly to the total memory the producer will use, but is not a hard bound since not all memory the producer uses is used for buffering. Some additional memory will be used for compression (if compression is enabled) as well as for maintaining in-flight requests.	33554432	Integer
circularTopicDetection (producer)	If the option is true, then KafkaProducer will detect if the message is attempted to be sent back to the same topic it may come from, if the message was original from a kafka consumer. If the KafkaConstants.TOPIC header is the same as the original kafka consumer topic, then the header setting is ignored, and the topic of the producer endpoint is used. In other words this avoids sending the same message back to where it came from. This option is not in use if the option bridgeEndpoint is set to true.	true	boolean
compressionCodec (producer)	This parameter allows you to specify the compression codec for all data generated by this producer. Valid values are none, gzip and snappy.	none	String
connectionMaxIdleMs (producer)	Close idle connections after the number of milliseconds specified by this config.	540000	Integer
enableIdempotence (producer)	If set to 'true' the producer will ensure that exactly one copy of each message is written in the stream. If 'false', producer retries may write duplicates of the retried message in the stream. If set to true this option will require max.in.flight.requests.per.connection to be set to 1 and retries cannot be zero and additionally acks must be set to 'all'.	false	boolean
kafkaHeaderSerializer (producer)	Sets custom KafkaHeaderDeserializer for serialization camel headers values to kafka headers values.		KafkaHeaderSerializer
key (producer)	The record key (or null if no key is specified). If this option has been configured then it take precedence over header KafkaConstants#KEY		String
keySerializerClass (producer)	The serializer class for keys (defaults to the same as for messages if nothing is given).	org.apache.kafka.common.serialization.StringSerializer	String
lingerMs (producer)	The producer groups together any records that arrive in between request transmissions into a single batched request. Normally this occurs only under load when records arrive faster than they can be sent out. However in some circumstances the client may want to reduce the number of requests even under moderate load. This setting accomplishes this by adding a small amount of artificial delaythat is, rather than immediately sending out a record the producer will wait for up to the given delay to allow other records to be sent so that the sends can be batched together. This can be thought of as analogous to Nagle’s algorithm in TCP. This setting gives the upper bound on the delay for batching: once we get batch.size worth of records for a partition it will be sent immediately regardless of this setting, however if we have fewer than this many bytes accumulated for this partition we will 'linger' for the specified time waiting for more records to show up. This setting defaults to 0 (i.e. no delay). Setting linger.ms=5, for example, would have the effect of reducing the number of requests sent but would add up to 5ms of latency to records sent in the absense of load.	0	Integer
maxBlockMs (producer)	The configuration controls how long sending to kafka will block. These methods can be blocked for multiple reasons. For e.g: buffer full, metadata unavailable.This configuration imposes maximum limit on the total time spent in fetching metadata, serialization of key and value, partitioning and allocation of buffer memory when doing a send(). In case of partitionsFor(), this configuration imposes a maximum time threshold on waiting for metadata	60000	Integer
maxInFlightRequest (producer)	The maximum number of unacknowledged requests the client will send on a single connection before blocking. Note that if this setting is set to be greater than 1 and there are failed sends, there is a risk of message re-ordering due to retries (i.e., if retries are enabled).	5	Integer
maxRequestSize (producer)	The maximum size of a request. This is also effectively a cap on the maximum record size. Note that the server has its own cap on record size which may be different from this. This setting will limit the number of record batches the producer will send in a single request to avoid sending huge requests.	1048576	Integer
metadataMaxAgeMs (producer)	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.	300000	Integer
metricReporters (producer)	A list of classes to use as metrics reporters. Implementing the MetricReporter interface allows plugging in classes that will be notified of new metric creation. The JmxReporter is always included to register JMX statistics.		String
metricsSampleWindowMs (producer)	The number of samples maintained to compute metrics.	30000	Integer
noOfMetricsSample (producer)	The number of samples maintained to compute metrics.	2	Integer
partitioner (producer)	The partitioner class for partitioning messages amongst sub-topics. The default partitioner is based on the hash of the key.	org.apache.kafka.clients.producer.internals.DefaultPartitioner	String
partitionKey (producer)	The partition to which the record will be sent (or null if no partition was specified). If this option has been configured then it take precedence over header KafkaConstants#PARTITION_KEY		Integer
producerBatchSize (producer)	The producer will attempt to batch records together into fewer requests whenever multiple records are being sent to the same partition. This helps performance on both the client and the server. This configuration controls the default batch size in bytes. No attempt will be made to batch records larger than this size.Requests sent to brokers will contain multiple batches, one for each partition with data available to be sent.A small batch size will make batching less common and may reduce throughput (a batch size of zero will disable batching entirely). A very large batch size may use memory a bit more wastefully as we will always allocate a buffer of the specified batch size in anticipation of additional records.	16384	Integer
queueBufferingMaxMessages (producer)	The maximum number of unsent messages that can be queued up the producer when using async mode before either the producer must be blocked or data must be dropped.	10000	Integer
receiveBufferBytes (producer)	The size of the TCP receive buffer (SO_RCVBUF) to use when reading data.	65536	Integer
reconnectBackoffMs (producer)	The 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 requests sent by the consumer to the broker.	50	Integer
recordMetadata (producer)	Whether the producer should store the RecordMetadata results from sending to Kafka. The results are stored in a List containing the RecordMetadata metadata’s. The list is stored on a header with the key KafkaConstants#KAFKA_RECORDMETA	true	boolean
requestRequiredAcks (producer)	The number of acknowledgments the producer requires the leader to have received before considering a request complete. This controls the durability of records that are sent. The following settings are common: acks=0 If set to zero then the producer will not wait for any acknowledgment from the server at all. The record will be immediately added to the socket buffer and considered sent. No guarantee can be made that the server has received the record in this case, and the retries configuration will not take effect (as the client won’t generally know of any failures). The offset given back for each record will always be set to -1. acks=1 This will mean the leader will write the record to its local log but will respond without awaiting full acknowledgement from all followers. In this case should the leader fail immediately after acknowledging the record but before the followers have replicated it then the record will be lost. acks=all This means the leader will wait for the full set of in-sync replicas to acknowledge the record. This guarantees that the record will not be lost as long as at least one in-sync replica remains alive. This is the strongest available guarantee.	1	String
requestTimeoutMs (producer)	The amount of time the broker will wait trying to meet the request.required.acks requirement before sending back an error to the client.	305000	Integer
retries (producer)	Setting a value greater than zero will cause the client to resend any record whose send fails with a potentially transient error. Note that this retry is no different than if the client resent the record upon receiving the error. Allowing retries will potentially change the ordering of records because if two records are sent to a single partition, and the first fails and is retried but the second succeeds, then the second record may appear first.	0	Integer
retryBackoffMs (producer)	Before each retry, the producer refreshes the metadata of relevant topics to see if a new leader has been elected. Since leader election takes a bit of time, this property specifies the amount of time that the producer waits before refreshing the metadata.	100	Integer
sendBufferBytes (producer)	Socket write buffer size	131072	Integer
serializerClass (producer)	The serializer class for messages.	org.apache.kafka.common.serialization.StringSerializer	String
workerPool (producer)	To use a custom worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing.		ExecutorService
workerPoolCoreSize (producer)	Number of core threads for the worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing.	10	Integer
workerPoolMaxSize (producer)	Maximum number of threads for the worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing.	20	Integer
synchronous (advanced)	Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported).	false	boolean
interceptorClasses (monitoring)	Sets interceptors for producer or consumers. Producer interceptors have to be classes implementing org.apache.kafka.clients.producer.ProducerInterceptor Consumer interceptors have to be classes implementing org.apache.kafka.clients.consumer.ConsumerInterceptor Note that if you use Producer interceptor on a consumer it will throw a class cast exception in runtime		String
kerberosBeforeReloginMin Time (security)	Login thread sleep time between refresh attempts.	60000	Integer
kerberosInitCmd (security)	Kerberos kinit command path. Default is /usr/bin/kinit	/usr/bin/kinit	String
kerberosPrincipalToLocal Rules (security)	A list of rules for mapping from principal names to short names (typically operating system usernames). The rules are evaluated in order and the first rule that matches a principal name is used to map it to a short name. Any later rules in the list are ignored. By default, principal names of the form username/hostnameREALM are mapped to username. For more details on the format please see security authorization and acls. Multiple values can be separated by comma	DEFAULT	String
kerberosRenewJitter (security)	Percentage of random jitter added to the renewal time.	0.05	Double
kerberosRenewWindowFactor (security)	Login thread will sleep until the specified window factor of time from last refresh to ticket’s expiry has been reached, at which time it will try to renew the ticket.	0.8	Double
saslJaasConfig (security)	Expose the kafka sasl.jaas.config parameter Example: org.apache.kafka.common.security.plain.PlainLoginModule required username=USERNAME password=PASSWORD;		String
saslKerberosServiceName (security)	The Kerberos principal name that Kafka runs as. This can be defined either in Kafka’s JAAS config or in Kafka’s config.		String
saslMechanism (security)	The Simple Authentication and Security Layer (SASL) Mechanism used. For the valid values see http://www.iana.org/assignments/sasl-mechanisms/sasl-mechanisms.xhtml	GSSAPI	String
securityProtocol (security)	Protocol used to communicate with brokers. Currently only PLAINTEXT and SSL are supported.	PLAINTEXT	String
sslCipherSuites (security)	A list of cipher suites. This is a named combination of authentication, encryption, MAC and key exchange algorithm used to negotiate the security settings for a network connection using TLS or SSL network protocol.By default all the available cipher suites are supported.		String
sslContextParameters (security)	SSL configuration using a Camel SSLContextParameters object. If configured it’s applied before the other SSL endpoint parameters.		SSLContextParameters
sslEnabledProtocols (security)	The list of protocols enabled for SSL connections. TLSv1.2, TLSv1.1 and TLSv1 are enabled by default.	TLSv1.2,TLSv1.1,TLSv1	String
sslEndpointAlgorithm (security)	The endpoint identification algorithm to validate server hostname using server certificate.		String
sslKeymanagerAlgorithm (security)	The algorithm used by key manager factory for SSL connections. Default value is the key manager factory algorithm configured for the Java Virtual Machine.	SunX509	String
sslKeyPassword (security)	The password of the private key in the key store file. This is optional for client.		String
sslKeystoreLocation (security)	The location of the key store file. This is optional for client and can be used for two-way authentication for client.		String
sslKeystorePassword (security)	The store password for the key store file.This is optional for client and only needed if ssl.keystore.location is configured.		String
sslKeystoreType (security)	The file format of the key store file. This is optional for client. Default value is JKS	JKS	String
sslProtocol (security)	The SSL protocol used to generate the SSLContext. Default setting is TLS, which is fine for most cases. Allowed values in recent JVMs are TLS, TLSv1.1 and TLSv1.2. SSL, SSLv2 and SSLv3 may be supported in older JVMs, but their usage is discouraged due to known security vulnerabilities.	TLS	String
sslProvider (security)	The name of the security provider used for SSL connections. Default value is the default security provider of the JVM.		String
sslTrustmanagerAlgorithm (security)	The algorithm used by trust manager factory for SSL connections. Default value is the trust manager factory algorithm configured for the Java Virtual Machine.	PKIX	String
sslTruststoreLocation (security)	The location of the trust store file.		String
sslTruststorePassword (security)	The password for the trust store file.		String
sslTruststoreType (security)	The file format of the trust store file. Default value is JKS.	JKS	String

190.3. Spring Boot Auto-Configuration

The component supports 98 options, which are listed below.

Name	Description	Default	Type
camel.component.kafka.allow-manual-commit	Whether to allow doing manual commits via KafkaManualCommit. If this option is enabled then an instance of KafkaManualCommit is stored on the Exchange message header, which allows end users to access this API and perform manual offset commits via the Kafka consumer.	false	Boolean
camel.component.kafka.break-on-first-error	This options controls what happens when a consumer is processing an exchange and it fails. If the option is false then the consumer continues to the next message and processes it. If the option is true then the consumer breaks out, and will seek back to offset of the message that caused a failure, and then re-attempt to process this message. However this can lead to endless processing of the same message if its bound to fail every time, eg a poison message. Therefore its recommended to deal with that for example by using Camel’s error handler.	false	Boolean
camel.component.kafka.brokers	URL of the Kafka brokers to use. The format is host1:port1,host2:port2, and the list can be a subset of brokers or a VIP pointing to a subset of brokers. This option is known as bootstrap.servers in the Kafka documentation.		String
camel.component.kafka.configuration.allow-manual-commit	Whether to allow doing manual commits via KafkaManualCommit. If this option is enabled then an instance of KafkaManualCommit is stored on the Exchange message header, which allows end users to access this API and perform manual offset commits via the Kafka consumer.	false	Boolean
camel.component.kafka.configuration.auto-commit-enable	If true, periodically commit to ZooKeeper the offset of messages already fetched by the consumer. This committed offset will be used when the process fails as the position from which the new consumer will begin.	true	Boolean
camel.component.kafka.configuration.auto-commit-interval-ms	The frequency in ms that the consumer offsets are committed to zookeeper.	5000	Integer
camel.component.kafka.configuration.auto-commit-on-stop	Whether to perform an explicit auto commit when the consumer stops to ensure the broker has a commit from the last consumed message. This requires the option autoCommitEnable is turned on. The possible values are: sync, async, or none. And sync is the default value.	sync	String
camel.component.kafka.configuration.auto-offset-reset	What to do when there is no initial offset in ZooKeeper or if an offset is out of range: earliest : automatically reset the offset to the earliest offset latest : automatically reset the offset to the latest offset fail: throw exception to the consumer	latest	String
camel.component.kafka.configuration.break-on-first-error	This options controls what happens when a consumer is processing an exchange and it fails. If the option is false then the consumer continues to the next message and processes it. If the option is true then the consumer breaks out, and will seek back to offset of the message that caused a failure, and then re-attempt to process this message. However this can lead to endless processing of the same message if its bound to fail every time, eg a poison message. Therefore its recommended to deal with that for example by using Camel’s error handler.	false	Boolean
camel.component.kafka.configuration.bridge-endpoint	If the option is true, then KafkaProducer will ignore the KafkaConstants.TOPIC header setting of the inbound message.	false	Boolean
camel.component.kafka.configuration.brokers	URL of the Kafka brokers to use. The format is host1:port1,host2:port2, and the list can be a subset of brokers or a VIP pointing to a subset of brokers. This option is known as bootstrap.servers in the Kafka documentation.		String
camel.component.kafka.configuration.buffer-memory-size	The total bytes of memory the producer can use to buffer records waiting to be sent to the server. If records are sent faster than they can be delivered to the server the producer will either block or throw an exception based on the preference specified by block.on.buffer.full.This setting should correspond roughly to the total memory the producer will use, but is not a hard bound since not all memory the producer uses is used for buffering. Some additional memory will be used for compression (if compression is enabled) as well as for maintaining in-flight requests.	33554432	Integer
camel.component.kafka.configuration.check-crcs	Automatically check the CRC32 of the records consumed. This ensures no on-the-wire or on-disk corruption to the messages occurred. This check adds some overhead, so it may be disabled in cases seeking extreme performance.	true	Boolean
camel.component.kafka.configuration.circular-topic-detection	If the option is true, then KafkaProducer will detect if the message is attempted to be sent back to the same topic it may come from, if the message was original from a kafka consumer. If the KafkaConstants.TOPIC header is the same as the original kafka consumer topic, then the header setting is ignored, and the topic of the producer endpoint is used. In other words this avoids sending the same message back to where it came from. This option is not in use if the option bridgeEndpoint is set to true.	true	Boolean
camel.component.kafka.configuration.client-id	The client id is a user-specified string sent in each request to help trace calls. It should logically identify the application making the request.		String
camel.component.kafka.configuration.compression-codec	This parameter allows you to specify the compression codec for all data generated by this producer. Valid values are none, gzip and snappy.	none	String
camel.component.kafka.configuration.connection-max-idle-ms	Close idle connections after the number of milliseconds specified by this config.	540000	Integer
camel.component.kafka.configuration.consumer-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.	40000	Integer
camel.component.kafka.configuration.consumer-streams	Number of concurrent consumers on the consumer	10	Integer
camel.component.kafka.configuration.consumers-count	The number of consumers that connect to kafka server	1	Integer
camel.component.kafka.configuration.enable-idempotence	If set to 'true' the producer will ensure that exactly one copy of each message is written in the stream. If 'false', producer retries may write duplicates of the retried message in the stream. If set to true this option will require max.in.flight.requests.per.connection to be set to 1 and retries cannot be zero and additionally acks must be set to 'all'.	false	Boolean
camel.component.kafka.configuration.fetch-max-bytes	The maximum amount of data the server should return for a fetch request This is not an absolute maximum, if the first message in the first non-empty partition of the fetch is larger than this value, the message will still be returned to ensure that the consumer can make progress. The maximum message size accepted by the broker is defined via message.max.bytes (broker config) or max.message.bytes (topic config). Note that the consumer performs multiple fetches in parallel.	52428800	Integer
camel.component.kafka.configuration.fetch-min-bytes	The minimum amount of data the server should return for a fetch request. If insufficient data is available the request will wait for that much data to accumulate before answering the request.	1	Integer
camel.component.kafka.configuration.fetch-wait-max-ms	The maximum amount of time the server will block before answering the fetch request if there isn’t sufficient data to immediately satisfy fetch.min.bytes	500	Integer
camel.component.kafka.configuration.group-id	A string that uniquely identifies the group of consumer processes to which this consumer belongs. By setting the same group id multiple processes indicate that they are all part of the same consumer group. This option is required for consumers.		String
camel.component.kafka.configuration.header-filter-strategy	To use a custom HeaderFilterStrategy to filter header to and from Camel message.		HeaderFilterStrategy
camel.component.kafka.configuration.heartbeat-interval-ms	The expected time between heartbeats to the consumer coordinator when using Kafka’s group management facilities. Heartbeats are used to ensure that the consumer’s session stays active and to facilitate rebalancing when new consumers join or leave the group. The value must be set lower than session.timeout.ms, but typically should be set no higher than 1/3 of that value. It can be adjusted even lower to control the expected time for normal rebalances.	3000	Integer
camel.component.kafka.configuration.interceptor-classes	Sets interceptors for producer or consumers. Producer interceptors have to be classes implementing org.apache.kafka.clients.producer.ProducerInterceptor Consumer interceptors have to be classes implementing org.apache.kafka.clients.consumer.ConsumerInterceptor Note that if you use Producer interceptor on a consumer it will throw a class cast exception in runtime		String
camel.component.kafka.configuration.kafka-header-deserializer	Sets custom KafkaHeaderDeserializer for deserialization kafka headers values to camel headers values.		KafkaHeaderDeserializer
camel.component.kafka.configuration.kafka-header-serializer	Sets custom KafkaHeaderDeserializer for serialization camel headers values to kafka headers values.		KafkaHeaderSerializer
camel.component.kafka.configuration.kerberos-before-relogin-min-time	Login thread sleep time between refresh attempts.	60000	Integer
camel.component.kafka.configuration.kerberos-init-cmd	Kerberos kinit command path. Default is /usr/bin/kinit	/usr/bin/kinit	String
camel.component.kafka.configuration.kerberos-principal-to-local-rules	A list of rules for mapping from principal names to short names (typically operating system usernames). The rules are evaluated in order and the first rule that matches a principal name is used to map it to a short name. Any later rules in the list are ignored. By default, principal names of the form username/hostnameREALM are mapped to username. For more details on the format please see security authorization and acls. Multiple values can be separated by comma	DEFAULT	String
camel.component.kafka.configuration.kerberos-renew-jitter	Percentage of random jitter added to the renewal time.		Double
camel.component.kafka.configuration.kerberos-renew-window-factor	Login thread will sleep until the specified window factor of time from last refresh to ticket’s expiry has been reached, at which time it will try to renew the ticket.		Double
camel.component.kafka.configuration.key	The record key (or null if no key is specified). If this option has been configured then it take precedence over header KafkaConstants#KEY		String
camel.component.kafka.configuration.key-deserializer	Deserializer class for key that implements the Deserializer interface.	org.apache.kafka.common.serialization.StringDeserializer	String
camel.component.kafka.configuration.key-serializer-class	The serializer class for keys (defaults to the same as for messages if nothing is given).	org.apache.kafka.common.serialization.StringSerializer	String
camel.component.kafka.configuration.linger-ms	The producer groups together any records that arrive in between request transmissions into a single batched request. Normally this occurs only under load when records arrive faster than they can be sent out. However in some circumstances the client may want to reduce the number of requests even under moderate load. This setting accomplishes this by adding a small amount of artificial delaythat is, rather than immediately sending out a record the producer will wait for up to the given delay to allow other records to be sent so that the sends can be batched together. This can be thought of as analogous to Nagle’s algorithm in TCP. This setting gives the upper bound on the delay for batching: once we get batch.size worth of records for a partition it will be sent immediately regardless of this setting, however if we have fewer than this many bytes accumulated for this partition we will 'linger' for the specified time waiting for more records to show up. This setting defaults to 0 (i.e. no delay). Setting linger.ms=5, for example, would have the effect of reducing the number of requests sent but would add up to 5ms of latency to records sent in the absense of load.	0	Integer
camel.component.kafka.configuration.max-block-ms	The configuration controls how long sending to kafka will block. These methods can be blocked for multiple reasons. For e.g: buffer full, metadata unavailable.This configuration imposes maximum limit on the total time spent in fetching metadata, serialization of key and value, partitioning and allocation of buffer memory when doing a send(). In case of partitionsFor(), this configuration imposes a maximum time threshold on waiting for metadata	60000	Integer
camel.component.kafka.configuration.max-in-flight-request	The maximum number of unacknowledged requests the client will send on a single connection before blocking. Note that if this setting is set to be greater than 1 and there are failed sends, there is a risk of message re-ordering due to retries (i.e., if retries are enabled).	5	Integer
camel.component.kafka.configuration.max-partition-fetch-bytes	The maximum amount of data per-partition the server will return. The maximum total memory used for a request will be #partitions max.partition.fetch.bytes. This size must be at least as large as the maximum message size the server allows or else it is possible for the producer to send messages larger than the consumer can fetch. If that happens, the consumer can get stuck trying to fetch a large message on a certain partition.	1048576	Integer
camel.component.kafka.configuration.max-poll-interval-ms	The maximum delay between invocations of poll() when using consumer group management. This places an upper bound on the amount of time that the consumer can be idle before fetching more records. If poll() is not called before expiration of this timeout, then the consumer is considered failed and the group will rebalance in order to reassign the partitions to another member.		Long
camel.component.kafka.configuration.max-poll-records	The maximum number of records returned in a single call to poll()	500	Integer
camel.component.kafka.configuration.max-request-size	The maximum size of a request. This is also effectively a cap on the maximum record size. Note that the server has its own cap on record size which may be different from this. This setting will limit the number of record batches the producer will send in a single request to avoid sending huge requests.	1048576	Integer
camel.component.kafka.configuration.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.	300000	Integer
camel.component.kafka.configuration.metric-reporters	A list of classes to use as metrics reporters. Implementing the MetricReporter interface allows plugging in classes that will be notified of new metric creation. The JmxReporter is always included to register JMX statistics.		String
camel.component.kafka.configuration.metrics-sample-window-ms	The number of samples maintained to compute metrics.	30000	Integer
camel.component.kafka.configuration.no-of-metrics-sample	The number of samples maintained to compute metrics.	2	Integer
camel.component.kafka.configuration.offset-repository	The offset repository to use in order to locally store the offset of each partition of the topic. Defining one will disable the autocommit.		StateRepository
camel.component.kafka.configuration.partition-assignor	The class name of the partition assignment strategy that the client will use to distribute partition ownership amongst consumer instances when group management is used	org.apache.kafka.clients.consumer.RangeAssignor	String
camel.component.kafka.configuration.partition-key	The partition to which the record will be sent (or null if no partition was specified). If this option has been configured then it take precedence over header KafkaConstants#PARTITION_KEY		Integer
camel.component.kafka.configuration.partitioner	The partitioner class for partitioning messages amongst sub-topics. The default partitioner is based on the hash of the key.	org.apache.kafka.clients.producer.internals.DefaultPartitioner	String
camel.component.kafka.configuration.poll-timeout-ms	The timeout used when polling the KafkaConsumer.	5000	Long
camel.component.kafka.configuration.producer-batch-size	The producer will attempt to batch records together into fewer requests whenever multiple records are being sent to the same partition. This helps performance on both the client and the server. This configuration controls the default batch size in bytes. No attempt will be made to batch records larger than this size.Requests sent to brokers will contain multiple batches, one for each partition with data available to be sent.A small batch size will make batching less common and may reduce throughput (a batch size of zero will disable batching entirely). A very large batch size may use memory a bit more wastefully as we will always allocate a buffer of the specified batch size in anticipation of additional records.	16384	Integer
camel.component.kafka.configuration.queue-buffering-max-messages	The maximum number of unsent messages that can be queued up the producer when using async mode before either the producer must be blocked or data must be dropped.	10000	Integer
camel.component.kafka.configuration.receive-buffer-bytes	The size of the TCP receive buffer (SO_RCVBUF) to use when reading data.	65536	Integer
camel.component.kafka.configuration.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.	1000	Integer
camel.component.kafka.configuration.reconnect-backoff-ms	The 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 requests sent by the consumer to the broker.	50	Integer
camel.component.kafka.configuration.record-metadata	Whether the producer should store the RecordMetadata results from sending to Kafka. The results are stored in a List containing the RecordMetadata metadata’s. The list is stored on a header with the key KafkaConstants#KAFKA_RECORDMETA	true	Boolean
camel.component.kafka.configuration.request-required-acks	The number of acknowledgments the producer requires the leader to have received before considering a request complete. This controls the durability of records that are sent. The following settings are common: acks=0 If set to zero then the producer will not wait for any acknowledgment from the server at all. The record will be immediately added to the socket buffer and considered sent. No guarantee can be made that the server has received the record in this case, and the retries configuration will not take effect (as the client won’t generally know of any failures). The offset given back for each record will always be set to -1. acks=1 This will mean the leader will write the record to its local log but will respond without awaiting full acknowledgement from all followers. In this case should the leader fail immediately after acknowledging the record but before the followers have replicated it then the record will be lost. acks=all This means the leader will wait for the full set of in-sync replicas to acknowledge the record. This guarantees that the record will not be lost as long as at least one in-sync replica remains alive. This is the strongest available guarantee.	1	String
camel.component.kafka.configuration.request-timeout-ms	The amount of time the broker will wait trying to meet the request.required.acks requirement before sending back an error to the client.	305000	Integer
camel.component.kafka.configuration.retries	Setting a value greater than zero will cause the client to resend any record whose send fails with a potentially transient error. Note that this retry is no different than if the client resent the record upon receiving the error. Allowing retries will potentially change the ordering of records because if two records are sent to a single partition, and the first fails and is retried but the second succeeds, then the second record may appear first.	0	Integer
camel.component.kafka.configuration.retry-backoff-ms	Before each retry, the producer refreshes the metadata of relevant topics to see if a new leader has been elected. Since leader election takes a bit of time, this property specifies the amount of time that the producer waits before refreshing the metadata.	100	Integer
camel.component.kafka.configuration.sasl-jaas-config	Expose the kafka sasl.jaas.config parameter Example: org.apache.kafka.common.security.plain.PlainLoginModule required username=USERNAME password=PASSWORD;		String
camel.component.kafka.configuration.sasl-kerberos-service-name	The Kerberos principal name that Kafka runs as. This can be defined either in Kafka’s JAAS config or in Kafka’s config.		String
camel.component.kafka.configuration.sasl-mechanism	The Simple Authentication and Security Layer (SASL) Mechanism used. For the valid values see http://www.iana.org/assignments/sasl-mechanisms/sasl-mechanisms.xhtml	GSSAPI	String
camel.component.kafka.configuration.security-protocol	Protocol used to communicate with brokers. Currently only PLAINTEXT and SSL are supported.	PLAINTEXT	String
camel.component.kafka.configuration.seek-to	Set if KafkaConsumer will read from beginning or end on startup: beginning : read from beginning end : read from end This is replacing the earlier property seekToBeginning		String
camel.component.kafka.configuration.send-buffer-bytes	Socket write buffer size	131072	Integer
camel.component.kafka.configuration.serializer-class	The serializer class for messages.	org.apache.kafka.common.serialization.StringSerializer	String
camel.component.kafka.configuration.session-timeout-ms	The timeout used to detect failures when using Kafka’s group management facilities.	10000	Integer
camel.component.kafka.configuration.ssl-cipher-suites	A list of cipher suites. This is a named combination of authentication, encryption, MAC and key exchange algorithm used to negotiate the security settings for a network connection using TLS or SSL network protocol.By default all the available cipher suites are supported.		String
camel.component.kafka.configuration.ssl-context-parameters	SSL configuration using a Camel SSLContextParameters object. If configured it’s applied before the other SSL endpoint parameters.		SSLContextParameters
camel.component.kafka.configuration.ssl-enabled-protocols	The list of protocols enabled for SSL connections. TLSv1.2, TLSv1.1 and TLSv1 are enabled by default.	TLSv1.2,TLSv1.1,TLSv1	String
camel.component.kafka.configuration.ssl-endpoint-algorithm	The endpoint identification algorithm to validate server hostname using server certificate.		String
camel.component.kafka.configuration.ssl-key-password	The password of the private key in the key store file. This is optional for client.		String
camel.component.kafka.configuration.ssl-keymanager-algorithm	The algorithm used by key manager factory for SSL connections. Default value is the key manager factory algorithm configured for the Java Virtual Machine.	SunX509	String
camel.component.kafka.configuration.ssl-keystore-location	The location of the key store file. This is optional for client and can be used for two-way authentication for client.		String
camel.component.kafka.configuration.ssl-keystore-password	The store password for the key store file.This is optional for client and only needed if ssl.keystore.location is configured.		String
camel.component.kafka.configuration.ssl-keystore-type	The file format of the key store file. This is optional for client. Default value is JKS	JKS	String
camel.component.kafka.configuration.ssl-protocol	The SSL protocol used to generate the SSLContext. Default setting is TLS, which is fine for most cases. Allowed values in recent JVMs are TLS, TLSv1.1 and TLSv1.2. SSL, SSLv2 and SSLv3 may be supported in older JVMs, but their usage is discouraged due to known security vulnerabilities.	TLS	String
camel.component.kafka.configuration.ssl-provider	The name of the security provider used for SSL connections. Default value is the default security provider of the JVM.		String
camel.component.kafka.configuration.ssl-trustmanager-algorithm	The algorithm used by trust manager factory for SSL connections. Default value is the trust manager factory algorithm configured for the Java Virtual Machine.	PKIX	String
camel.component.kafka.configuration.ssl-truststore-location	The location of the trust store file.		String
camel.component.kafka.configuration.ssl-truststore-password	The password for the trust store file.		String
camel.component.kafka.configuration.ssl-truststore-type	The file format of the trust store file. Default value is JKS.	JKS	String
camel.component.kafka.configuration.topic	Name of the topic to use. On the consumer you can use comma to separate multiple topics. A producer can only send a message to a single topic.		String
camel.component.kafka.configuration.topic-is-pattern	Whether the topic is a pattern (regular expression). This can be used to subscribe to dynamic number of topics matching the pattern.	false	Boolean
camel.component.kafka.configuration.value-deserializer	Deserializer class for value that implements the Deserializer interface.	org.apache.kafka.common.serialization.StringDeserializer	String
camel.component.kafka.configuration.worker-pool	To use a custom worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing.		ExecutorService
camel.component.kafka.configuration.worker-pool-core-size	Number of core threads for the worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing.	10	Integer
camel.component.kafka.configuration.worker-pool-max-size	Maximum number of threads for the worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing.	20	Integer
camel.component.kafka.enabled	Enable kafka component	true	Boolean
camel.component.kafka.kafka-manual-commit-factory	Factory to use for creating KafkaManualCommit instances. This allows to plugin a custom factory to create custom KafkaManualCommit instances in case special logic is needed when doing manual commits that deviates from the default implementation that comes out of the box. The option is a org.apache.camel.component.kafka.KafkaManualCommitFactory type.		String
camel.component.kafka.resolve-property-placeholders	Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders.	true	Boolean
camel.component.kafka.use-global-ssl-context-parameters	Enable usage of global SSL context parameters.	false	Boolean
camel.component.kafka.worker-pool	To use a shared custom worker pool for continue routing Exchange after kafka server has acknowledge the message that was sent to it from KafkaProducer using asynchronous non-blocking processing. If using this option then you must handle the lifecycle of the thread pool to shut the pool down when no longer needed. The option is a java.util.concurrent.ExecutorService type.		String

For more information about Producer/Consumer configuration:

http://kafka.apache.org/documentation.html#newconsumerconfigs http://kafka.apache.org/documentation.html#producerconfigs

190.4. Message headers

190.4.1. Consumer headers

The following headers are available when consuming messages from Kafka.

Header constant	Header value	Type	Description
`KafkaConstants.TOPIC`	`"kafka.TOPIC"`	`String`	The topic from where the message originated
`KafkaConstants.PARTITION`	`"kafka.PARTITION"`	`Integer`	The partition where the message was stored
`KafkaConstants.OFFSET`	`"kafka.OFFSET"`	`Long`	The offset of the message
`KafkaConstants.KEY`	`"kafka.KEY"`	`Object`	The key of the message if configured
`KafkaConstants.HEADERS`	`"kafka.HEADERS"`	`org.apache.kafka.common.header.Headers`	The record headers
`KafkaConstants.LAST_RECORD_BEFORE_COMMIT`	`"kafka.LAST_RECORD_BEFORE_COMMIT"`	`Boolean`	Whether or not it’s the last record before commit (only available if `autoCommitEnable` endpoint parameter is `false`)
`KafkaConstants.MANUAL_COMMIT`	`"CamelKafkaManualCommit"`	`KafkaManualCommit`	Can be used for forcing manual offset commit when using Kafka consumer.

190.4.2. Producer headers

Before sending a message to Kafka you can configure the following headers.

Header constant	Header value	Type	Description
`KafkaConstants.KEY`	`"kafka.KEY"`	`Object`	Required The key of the message in order to ensure that all related message goes in the same partition
`KafkaConstants.TOPIC`	`"kafka.TOPIC"`	`String`	The topic to which send the message (only read if the `bridgeEndpoint` endpoint parameter is `true`)
`KafkaConstants.PARTITION_KEY`	`"kafka.PARTITION_KEY"`	`Integer`	Explicitly specify the partition (only used if the `KafkaConstants.KEY` header is defined)

After the message is sent to Kafka, the following headers are available

Header constant	Header value	Type	Description
`KafkaConstants.KAFKA_RECORDMETA`	`"org.apache.kafka.clients.producer.RecordMetadata"`	`List<RecordMetadata>`	The metadata (only configured if `recordMetadata` endpoint parameter is `true`

190.5. Samples

190.5.1. Consuming messages from Kafka

Here is the minimal route you need in order to read messages from Kafka.

from("kafka:test?brokers=localhost:9092")
    .log("Message received from Kafka : ${body}")
    .log("    on the topic ${headers[kafka.TOPIC]}")
    .log("    on the partition ${headers[kafka.PARTITION]}")
    .log("    with the offset ${headers[kafka.OFFSET]}")
    .log("    with the key ${headers[kafka.KEY]}")

If you need to consume messages from multiple topics you can use a comma separated list of topic names

from("kafka:test,test1,test2?brokers=localhost:9092")
    .log("Message received from Kafka : ${body}")
    .log("    on the topic ${headers[kafka.TOPIC]}")
    .log("    on the partition ${headers[kafka.PARTITION]}")
    .log("    with the offset ${headers[kafka.OFFSET]}")
    .log("    with the key ${headers[kafka.KEY]}")

When consuming messages from Kafka you can use your own offset management and not delegate this management to Kafka. In order to keep the offsets the component needs a StateRepository implementation such as FileStateRepository. This bean should be available in the registry. Here how to use it :

// Create the repository in which the Kafka offsets will be persisted
FileStateRepository repository = FileStateRepository.fileStateRepository(new File("/path/to/repo.dat"));

// Bind this repository into the Camel registry
JndiRegistry registry = new JndiRegistry();
registry.bind("offsetRepo", repository);

// Configure the camel context
DefaultCamelContext camelContext = new DefaultCamelContext(registry);
camelContext.addRoutes(new RouteBuilder() {
    @Override
    public void configure() throws Exception {
        from("kafka:" + TOPIC + "?brokers=localhost:{{kafkaPort}}" +
                     // Setup the topic and broker address
                     "&groupId=A" +
                     // The consumer processor group ID
                     "&autoOffsetReset=earliest" +
                     // Ask to start from the beginning if we have unknown offset
                     "&offsetRepository=#offsetRepo")
                     // Keep the offsets in the previously configured repository
                .to("mock:result");
    }
});

190.5.2. Producing messages to Kafka

Here is the minimal route you need in order to write messages to Kafka.

from("direct:start")
    .setBody(constant("Message from Camel"))          // Message to send
    .setHeader(KafkaConstants.KEY, constant("Camel")) // Key of the message
    .to("kafka:test?brokers=localhost:9092");

190.6. SSL configuration

You have 2 different ways to configure the SSL communication on the Kafka` component.

The first way is through the many SSL endpoint parameters

from("kafka:" + TOPIC + "?brokers=localhost:{{kafkaPort}}" +
             "&groupId=A" +
             "&sslKeystoreLocation=/path/to/keystore.jks" +
             "&sslKeystorePassword=changeit" +
             "&sslKeyPassword=changeit" +
             "&securityProtocol=SSL")
        .to("mock:result");

The second way is to use the sslContextParameters endpoint parameter.

// Configure the SSLContextParameters object
KeyStoreParameters ksp = new KeyStoreParameters();
ksp.setResource("/path/to/keystore.jks");
ksp.setPassword("changeit");
KeyManagersParameters kmp = new KeyManagersParameters();
kmp.setKeyStore(ksp);
kmp.setKeyPassword("changeit");
SSLContextParameters scp = new SSLContextParameters();
scp.setKeyManagers(kmp);

// Bind this SSLContextParameters into the Camel registry
JndiRegistry registry = new JndiRegistry();
registry.bind("ssl", scp);

// Configure the camel context
DefaultCamelContext camelContext = new DefaultCamelContext(registry);
camelContext.addRoutes(new RouteBuilder() {
    @Override
    public void configure() throws Exception {
        from("kafka:" + TOPIC + "?brokers=localhost:{{kafkaPort}}" +
                     // Setup the topic and broker address
                     "&groupId=A" +
                     // The consumer processor group ID
                     "&sslContextParameters=#ssl" +
                     // The security protocol
                     "&securityProtocol=SSL)
                     // Reference the SSL configuration
                .to("mock:result");
    }
});

190.7. Using the Kafka idempotent repository

Available from Camel 2.19

The camel-kafka library provides a Kafka topic-based idempotent repository. This repository stores broadcasts all changes to idempotent state (add/remove) in a Kafka topic, and populates a local in-memory cache for each repository’s process instance through event sourcing.

The topic used must be unique per idempotent repository instance. The mechanism does not have any requirements about the number of topic partitions; as the repository consumes from all partitions at the same time. It also does not have any requirements about the replication factor of the topic.

Each repository instance that uses the topic (e.g. typically on different machines running in parallel) controls its own consumer group, so in a cluster of 10 Camel processes using the same topic each will control its own offset.

On startup, the instance subscribes to the topic and rewinds the offset to the beginning, rebuilding the cache to the latest state. The cache will not be considered warmed up until one poll of pollDurationMs in length returns 0 records. Startup will not be completed until either the cache has warmed up, or 30 seconds go by; if the latter happens the idempotent repository may be in an inconsistent state until its consumer catches up to the end of the topic.

A KafkaIdempotentRepository has the following properties:

Property	Description
`topic`	The name of the Kafka topic to use to broadcast changes. (required)
`bootstrapServers`	The `bootstrap.servers` property on the internal Kafka producer and consumer. Use this as shorthand if not setting `consumerConfig` and `producerConfig`. If used, this component will apply sensible default configurations for the producer and consumer.
`producerConfig`	Sets the properties that will be used by the Kafka producer that broadcasts changes. Overrides `bootstrapServers`, so must define the Kafka `bootstrap.servers` property itself
`consumerConfig`	Sets the properties that will be used by the Kafka consumer that populates the cache from the topic. Overrides `bootstrapServers`, so must define the Kafka `bootstrap.servers` property itself
`maxCacheSize`	How many of the most recently used keys should be stored in memory (default 1000).
`pollDurationMs`	The poll duration of the Kafka consumer. The local caches are updated immediately. This value will affect how far behind other peers that update their caches from the topic are relative to the idempotent consumer instance that sent the cache action message. The default value of this is 100 ms. If setting this value explicitly, be aware that there is a tradeoff between the remote cache liveness and the volume of network traffic between this repository’s consumer and the Kafka brokers. The cache warmup process also depends on there being one poll that fetches nothing - this indicates that the stream has been consumed up to the current point. If the poll duration is excessively long for the rate at which messages are sent on the topic, there exists a possibility that the cache cannot be warmed up and will operate in an inconsistent state relative to its peers until it catches up.

The repository can be instantiated by defining the topic and bootstrapServers, or the producerConfig and consumerConfig property sets can be explicitly defined to enable features such as SSL/SASL.

To use, this repository must be placed in the Camel registry, either manually or by registration as a bean in Spring/Blueprint, as it is CamelContext aware.

Sample usage is as follows:

KafkaIdempotentRepository kafkaIdempotentRepository = new KafkaIdempotentRepository("idempotent-db-inserts", "localhost:9091");

SimpleRegistry registry = new SimpleRegistry();
registry.put("insertDbIdemRepo", kafkaIdempotentRepository); // must be registered in the registry, to enable access to the CamelContext
CamelContext context = new CamelContext(registry);

// later in RouteBuilder...
from("direct:performInsert")
    .idempotentConsumer(header("id")).messageIdRepositoryRef("insertDbIdemRepo")
        // once-only insert into database
    .end()

In XML:

<!-- simple -->
<bean id="insertDbIdemRepo"
  class="org.apache.camel.processor.idempotent.kafka.KafkaIdempotentRepository">
  <property name="topic" value="idempotent-db-inserts"/>
  <property name="bootstrapServers" value="localhost:9091"/>
</bean>

<!-- complex -->
<bean id="insertDbIdemRepo"
  class="org.apache.camel.processor.idempotent.kafka.KafkaIdempotentRepository">
  <property name="topic" value="idempotent-db-inserts"/>
  <property name="maxCacheSize" value="10000"/>
  <property name="consumerConfig">
    <props>
      <prop key="bootstrap.servers">localhost:9091</prop>
    </props>
  </property>
  <property name="producerConfig">
    <props>
      <prop key="bootstrap.servers">localhost:9091</prop>
    </props>
  </property>
</bean>

190.8. Using manual commit with Kafka consumer

Available as of Camel 2.21

By default the Kafka consumer will use auto commit, where the offset will be committed automatically in the background using a given interval.

In case you want to force manual commits, you can use KafkaManualCommit API from the Camel Exchange, stored on the message header. This requires to turn on manual commits by either setting the option allowManualCommit to true on the KafkaComponent or on the endpoint, for example:

KafkaComponent kafka = new KafkaComponent();
kafka.setAllowManualCommit(true);
...
camelContext.addComponent("kafka", kafka);

You can then use the KafkaManualCommit from Java code such as a Camel Processor:

public void process(Exchange exchange) {
    KafkaManualCommit manual =
        exchange.getIn().getHeader(KafkaConstants.MANUAL_COMMIT, KafkaManualCommit.class);
    manual.commitSync();
}

This will force a synchronous commit which will block until the commit is acknowledge on Kafka, or if it fails an exception is thrown.

If you want to use a custom implementation of KafkaManualCommit then you can configure a custom KafkaManualCommitFactory on the KafkaComponent that creates instances of your custom implementation.

190.9. Kafka Headers propagation

Available as of Camel 2.22

When consuming messages from Kafka, headers will be propagated to camel exchange headers automatically. Producing flow backed by same behaviour - camel headers of particular exchange will be propagated to kafka message headers.

Since kafka headers allows only byte[] values, in order camel exchnage header to be propagated its value should be serialized to bytes[], otherwise header will be skipped. Following header value types are supported: String, Integer, Long, Double, Boolean, byte[]. Note: all headers propagated from kafka to camel exchange will contain byte[] value by default. In order to override default functionality uri parameters can be set: kafkaHeaderDeserializer for from route and kafkaHeaderSerializer for to route. Example:

from("kafka:my_topic?kafkaHeaderDeserializer=#myDeserializer")
...
.to("kafka:my_topic?kafkaHeaderSerializer=#mySerializer")

By default all headers are being filtered by KafkaHeaderFilterStrategy. Strategy filters out headers which start with Camel or org.apache.camel prefixes. Default strategy can be overridden by using headerFilterStrategy uri parameter in both to and from routes:

from("kafka:my_topic?headerFilterStrategy=#myStrategy")
...
.to("kafka:my_topic?headerFilterStrategy=#myStrategy")

myStrategy object should be subclass of HeaderFilterStrategy and must be placed in the Camel registry, either manually or by registration as a bean in Spring/Blueprint, as it is CamelContext aware.