components/camel-kafka/src/main/docs/kafka-component.adoc

## Kafka Component

*Available as of Camel version 2.13*

The *kafka:* component is used for communicating with
http://kafka.apache.org/[Apache Kafka] message broker.

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

From Camel 2.17 onwards Scala is no longer used, as we use the kafka java client.

[source,xml]
------------------------------------------------------------
<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

[source,java]
---------------------------
kafka:topic[?options]

---------------------------


### Options


// component options: START
The Kafka component supports 5 options which are listed below.



[width="100%",cols="2,5,^1,2",options="header"]
|=======================================================================
| 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:port1host2: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
| **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
|=======================================================================
// component options: END



// endpoint options: START
The Kafka endpoint is configured using URI syntax:

    kafka:topic

with the following path and query parameters:

#### Path Parameters (1 parameters):

[width="100%",cols="2,5,^1,2",options="header"]
|=======================================================================
| 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 (82 parameters):

[width="100%",cols="2,5,^1,2",options="header"]
|=======================================================================
| Name | Description | Default | Type
| **brokers** (common) | URL of the Kafka brokers to use. The format is host1:port1host2: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
| **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: smallest : automatically reset the offset to the smallest offset largest : automatically reset the offset to the largest offset fail: throw exception to the consumer | latest | String
| **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
| **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
| **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. |  | String>
| **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
| **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 options 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
| **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
| **key** (producer) | The record key (or null if no key is specified). If this option has been configured then it take precedence over header link KafkaConstantsKEY |  | 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 link KafkaConstantsPARTITION_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 link KafkaConstantsKAFKA_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
| **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
|=======================================================================
// endpoint options: END

For more information about Producer/Consumer configuration:

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

### Message headers

#### Consumer headers

The following headers are available when consuming messages from Kafka.
[width="100%",cols="2m,2m,1m,5",options="header"]
|=================================================================================================================================================================================================================
| 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.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`)
|=================================================================================================================================================================================================================

#### Producer headers

Before sending a message to Kafka you can configure the following headers.
[width="100%",cols="2m,2m,1m,5",options="header"]
|============================================================================================================================================================================
| 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
[width="100%",cols="2m,2m,1m,5",options="header"]
|==============================================================================================================================================================================================
| 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.
[source,java]
-------------------------------------------------------------
from("kafka:test?brokers=localhost:9092&groupId=testing")
    .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 :
[source,java]
----------------------------------------------------------------------------------------------------------------------------
// 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}}" +
                     "&groupId=A" +                            //
                     "&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");
    }
});
----------------------------------------------------------------------------------------------------------------------------
[source,java]
----------------------------------------------------------------------------------------------------------------------------
// Create the repository in which the Kafka offsets will be persisted using Spring @Bean annotation
@Bean(name = "offsetRepo", initMethod = "start", destroyMethod = "stop")
private FileStateRepository fileStateRepository() {
        FileStateRepository fileStateRepository = FileStateRepository.fileStateRepository(new File("/path/to/repo.dat"));
        return fileStateRepository;
}

camelContext.addRoutes(new RouteBuilder() {
    @Override
    public void configure() throws Exception {
        from("kafka:" + TOPIC + "?brokers=localhost:{{kafkaPort}}" +
                     "&groupId=A" +                            //
                     "&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.
[source,java]
----------------------------------------------------------------------------
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
[source,java]
-------------------------------------------------------------
from("kafka:" + TOPIC + "?brokers=localhost:{{kafkaPort}}" +
             "&groupId=A" +
             "&sslKeystoreLocation=/path/to/keystore.jks" +
             "&sslKeystorePassword=changeit" +
             "&sslKeyPassword=changeit")
        .to("mock:result");
-------------------------------------------------------------

The second way is to use the `sslContextParameters` endpoint parameter.
[source,java]
--------------------------------------------------------------------------------------------------
// 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}}" +
                     "&groupId=A" +                            //
                     "&sslContextParameters=#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:
[width="100%",cols="2m,5",options="header"]
|=======================================================================
| 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:

[source,java]
-------------------------------------------------------------
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:

[source,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>
-------------------------------------------------------------


### Endpoints

Camel supports the link:message-endpoint.html[Message Endpoint] pattern
using the
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/Endpoint.html[Endpoint]
interface. Endpoints are usually created by a
link:component.html[Component] and Endpoints are usually referred to in
the link:dsl.html[DSL] via their link:uris.html[URIs].

From an Endpoint you can use the following methods

* http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/Endpoint.html#createProducer()[createProducer()]
will create a
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/Producer.html[Producer]
for sending message exchanges to the endpoint

* http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/Endpoint.html#createConsumer(org.apache.camel.Processor)[createConsumer()]
implements the link:event-driven-consumer.html[Event Driven Consumer]
pattern for consuming message exchanges from the endpoint via a
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/Processor.html[Processor]
when creating a
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/Consumer.html[Consumer]

* http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/Endpoint.html#createPollingConsumer()[createPollingConsumer()]
implements the link:polling-consumer.html[Polling Consumer] pattern for
consuming message exchanges from the endpoint via a
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/PollingConsumer.html[PollingConsumer]

### See Also

* link:configuring-camel.html[Configuring Camel]
* link:message-endpoint.html[Message Endpoint] pattern
* link:uris.html[URIs]
* link:writing-components.html[Writing Components]