Monix integration with Kafka

Work in progress!

1. Getting Started with Kafka 1.0.x or above
2. Getting Started with Kafka 0.11.x
3. Getting Started with Kafka 0.10.x
4. Getting Started with Kafka 0.9.x
5. Getting Started with Kafka 0.8.x (no longer supported)
6. Usage
7. How can I contribute to Monix-Kafka?
8. Maintainers
9. License

In SBT:

libraryDependencies += "io.monix" %% "monix-kafka-1x" % "1.0.0-RC6"

For kafka versions higher than 1.0.x also add a dependency override:

dependencyOverrides += "org.apache.kafka" % "kafka-clients" % "2.1.0"

Or in case you're interested in running the tests of this project, it now supports embedded kafka for integration testing. You can simply run:

sbt kafka1x/test

In SBT:

libraryDependencies += "io.monix" %% "monix-kafka-11" % "1.0.0-RC6"

Or in case you're interested in running the tests of this project, it now supports embedded kafka for integration testing. You can simply run:

sbt kafka11/test

In SBT:

libraryDependencies += "io.monix" %% "monix-kafka-10" % "1.0.0-RC6"

Or in case you're interested in running the tests of this project, it now supports embedded kafka for integration testing. You can simply run:

sbt kafka10/test

Please note that EmbeddedKafka is not supported for Kafka 0.9.x

In SBT:

libraryDependencies += "io.monix" %% "monix-kafka-9" % "1.0.0-RC6"

Or in case you're interested in running the tests of this project, first download the Kafka server, version 0.9.x from their download page (note that 0.10.x or higher do not work with 0.9), then as the quick start section says, open a terminal window and first start Zookeeper:

bin/zookeeper-server-start.sh config/zookeeper.properties

Then start Kafka:

bin/kafka-server-start.sh config/server.properties

Create the topic we need for our tests:

bin/kafka-topics.sh --create --zookeeper localhost:2181 \
  --replication-factor 1 --partitions 1 \
  --topic monix-kafka-tests

And run the tests:

sbt kafka9/test

Please note that support for Kafka 0.8.x is dropped and the last available version with this dependency is 0.14.

In SBT:

libraryDependencies += "io.monix" %% "monix-kafka-8" % "0.14"

Or in case you're interested in running the tests of this project, first download the Kafka server, version 0.8.x from their download page (note that 0.9.x or higher do not work with 0.8), then as the quick start section says, open a terminal window and first start Zookeeper:

bin/zookeeper-server-start.sh config/zookeeper.properties

Then start Kafka:

bin/kafka-server-start.sh config/server.properties

Create the topics we need for our tests:

bin/kafka-topics.sh --create --zookeeper localhost:2181 \
  --replication-factor 1 --partitions 1 \
  --topic monix-kafka-tests
bin/kafka-topics.sh --create --zookeeper localhost:2181 \
  --replication-factor 1 --partitions 1 \
  --topic monix-kafka-manual-commit-tests

And run the tests:

sbt kafka8/test

import monix.kafka._
import monix.execution.Scheduler

implicit val scheduler: Scheduler = monix.execution.Scheduler.global

// Init
val producerCfg = KafkaProducerConfig.default.copy(
  bootstrapServers = List("127.0.0.1:9092")
)

val producer = KafkaProducer[String,String](producerCfg, scheduler)

// For sending one message
val recordMetadataF = producer.send("my-topic", "my-message").runToFuture

// For closing the producer connection
val closeF = producer.close().runToFuture

Calling producer.send returns a Task of Option[RecordMetadata] which can then be run and transformed into a Future.

If the Task completes with None it means that producer.send method was called after the producer was closed and that the message wasn't successfully acknowledged by the Kafka broker. In case of the failure of the underlying Kafka client the producer will bubble up the exception and fail the Task. All successfully delivered messages will complete with Some[RecordMetadata].

For pushing an entire Observable to Apache Kafka:

import monix.kafka._
import monix.execution.Scheduler
import monix.reactive.Observable
import org.apache.kafka.clients.producer.ProducerRecord

implicit val scheduler: Scheduler = monix.execution.Scheduler.global

// Initializing the producer
val producerCfg = KafkaProducerConfig.default.copy(
  bootstrapServers = List("127.0.0.1:9092")
)

val producer = KafkaProducerSink[String,String](producerCfg, scheduler)

// Lets pretend we have this observable of records
val observable: Observable[ProducerRecord[String,String]] = ???

observable
  // on overflow, start dropping incoming events
  .whileBusyDrop
  // buffers into batches if the consumer is busy, up to a max size
  .bufferIntrospective(1024)
  // consume everything by pushing into Apache Kafka
  .consumeWith(producer)
  // ready, set, go!
  .runToFuture

There are several ways for consuming from Apache Kafka (Version 0.11.x and above):

Consumer which commits offsets itself:

import monix.kafka._

val consumerCfg = KafkaConsumerConfig.default.copy(
  bootstrapServers = List("127.0.0.1:9092"),
  groupId = "kafka-tests"
  // you can use this settings for At Most Once semantics:
  // observableCommitOrder = ObservableCommitOrder.BeforeAck
)

val observable =
  KafkaConsumerObservable[String,String](consumerCfg, List("my-topic"))
    .take(10000)
    .map(_.value())

Consumer which allows you to commit offsets manually:

import monix.kafka._

val consumerCfg = KafkaConsumerConfig.default.copy(
  bootstrapServers = List("127.0.0.1:9092"),
  groupId = "kafka-tests"
)

val observable =
  KafkaConsumerObservable.manualCommit[String,String](consumerCfg, List("my-topic"))
    .map(message => message.record.value() -> message.committableOffset)
    .mapEval { case (value, offset) => performBusinessLogic(value).map(_ => offset) }
    .bufferTimedAndCounted(1.second, 1000)
    .mapEval(offsets => CommittableOffsetBatch(offsets).commitSync())

Enjoy!

Starting from Kafka 0.10.1.0, there is max.poll.interval.ms setting that defines the maximum delay between invocations of poll(), if it is not called in that interval, then the consumer is considered failed and the group will rebalance in order to reassign the partitions to another member.

This was an issue in monix-kafka, since poll is not called until all previous consumed ones were processed, so that slow downstream subscribers were in risk of being kicked off the consumer group indefinitely.

It is resolved in 1.0.0-RC8 by introducing an internal poll heartbeat interval that runs in the background keeping the consumer alive.

We welcome contributions to all projects in the Monix organization and would love for you to help build Monix-Kafka. See our contributor guide for more information about how you can get involed.

The current maintainers (people who can merge pull requests) are:

• Alexandru Nedelcu (alexandru)
• Piotr Gawryś (Avasil)
• Leandro Bolivar (leandrob13)

All code in this repository is licensed under the Apache License, Version 2.0. See LICENSE.txt.