Kafka

Since Camel 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>

URI format

kafka:topic[?options]

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:

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

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

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

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

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

Message headers

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.

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

Samples

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");
    }
});

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");

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");
    }
});

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>

Using manual commit with Kafka consumer

Since 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.

Kafka Headers propagation

Since 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.

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