Rdkafka

The rdkafka gem is a modern Kafka client library for Ruby based on librdkafka. It wraps the production-ready C client using the ffi gem and targets Kafka 1.0+ and Ruby versions that are under security or active maintenance. We remove Ruby version from our CI builds if they become EOL.

rdkafka was written because we needed a reliable Ruby client for Kafka that supports modern Kafka at AppSignal. We run it in production on very high traffic systems.

This gem only provides a high-level Kafka consumer. If you are running an older version of Kafka and/or need the legacy simple consumer we suggest using the Hermann gem.

The most important pieces of a Kafka client are implemented. We're working towards feature completeness, you can track that here: https://github.com/appsignal/rdkafka-ruby/milestone/1

Table of content

• Installation
• Usage
  • Consuming messages
  • Producing messages
• Higher level libraries
  • Message processing frameworks
  • Message publishing libraries
• Development
• Example

Installation

This gem downloads and compiles librdkafka when it is installed. If you have any problems installing the gem please open an issue.

Usage

See the documentation for full details on how to use this gem. Two quick examples:

Consuming messages

Subscribe to a topic and get messages. Kafka will automatically spread the available partitions over consumers with the same group id.

config = {
  :"bootstrap.servers" => "localhost:9092",
  :"group.id" => "ruby-test"
}
consumer = Rdkafka::Config.new(config).consumer
consumer.subscribe("ruby-test-topic")

consumer.each do |message|
  puts "Message received: #{message}"
end

Producing messages

Produce a number of messages, put the delivery handles in an array and wait for them before exiting. This way the messages will be batched and sent to Kafka in an efficient way.

config = {:"bootstrap.servers" => "localhost:9092"}
producer = Rdkafka::Config.new(config).producer
delivery_handles = []

100.times do |i|
  puts "Producing message #{i}"
  delivery_handles << producer.produce(
      topic:   "ruby-test-topic",
      payload: "Payload #{i}",
      key:     "Key #{i}"
  )
end

delivery_handles.each(&:wait)

Note that creating a producer consumes some resources that will not be released until it #close is explicitly called, so be sure to call Config#producer only as necessary.

Higher level libraries

Currently, there are two actively developed frameworks based on rdkafka-ruby, that provide higher level API that can be used to work with Kafka messages and one library for publishing messages.

Message processing frameworks

• Karafka - Ruby and Rails efficient Kafka processing framework.
• Racecar - A simple framework for Kafka consumers in Ruby

Message publishing libraries

• WaterDrop – Standalone Karafka library for producing Kafka messages.

Development

A Docker Compose file is included to run Kafka and Zookeeper. To run that:

docker-compose up

Run bundle and cd ext && bundle exec rake && cd .. to download and compile librdkafka.

You can then run bundle exec rspec to run the tests. To see rdkafka debug output:

DEBUG_PRODUCER=true bundle exec rspec
DEBUG_CONSUMER=true bundle exec rspec

After running the tests you can bring the cluster down to start with a clean slate:

docker-compose down

Example

To see everything working run these in separate tabs:

bundle exec rake consume_messages
bundle exec rake produce_messages