Hermann

A Ruby gem implementing a Kafka Publisher and Consumer

On MRI (C-based Ruby), this library wraps the librdkafka library which is implemented in C.

On JRuby this library declares jar dependencies inside the .gemspec to express dependencies on the Java-based Kafka library provided by the Kafka project. Tools like jbundler will handle these declarations correctly.

Usage

Usage is modelled on the kafka-rb gem and is fairly straightforward.

• Kafka 0.8 is supported.
• Ruby 1.9.3, 2.1.1 and JRuby are tested against

Producer

Zookeeper discovery

Discover Kafka brokers through zookeeper. Looks at /brokers/ids in Zookeeper to find the list of brokers.

require 'hermann/producer'
require 'hermann/discovery/zookeeper'

broker_ids_array = Hermann::Discovery::Zookeeper.new('localhost:2181').get_brokers
producer = Hermann::Producer.new('topic', broker_ids_array)

promise = producer.push('hello world') # send message to kafka
promise.value                          # forces the Concurrent::Promise to finish excuting (#value!)
promise.state                          # the state of the promise

MRI only

require 'hermann/producer'

broker_ids_array = Hermann::Discovery::Zookeeper.new('localhost:2181').get_brokers
p = Hermann::Producer.new('topic', broker_ids_array)  # arguments topic, list of brokers
f = p.push('hello world from mri')
f.state
p.tick_reactor
f.state

Consumer

Messages can be consumed by calling the consume method and passing a block to handle the yielded messages. The consume method blocks, so take care to handle that functionality appropriately (i.e. use Concurrent::Promise, Thread, etc).

(JRuby)

require 'hermann'
require 'hermann/consumer'
require 'hermann_jars'

topic     = 'topic'
new_topic = 'other_topic'

the_consumer = Hermann::Consumer.new(topic, zookeepers: "localhost:2181", group_id: "group1")

the_consumer.consume(new_topic) do |msg|   # can change topic with optional argument to .consume
  puts "Recv: #{msg}"
end

(MRI)

MRI currently has no zookeeper / client group support.

require 'hermann'
require 'hermann/consumer'

topic     = 'topic'
new_topic = 'other_topic'

the_consumer = Hermann::Consumer.new(topic, brokers: "localhost:9092", partition: 1)

the_consumer.consume(new_topic) do |msg, key, offset|   # can change topic with optional argument to .consume
  puts "Recv: #{msg}, key: #{key}, offset: #{offset}"
end

Metadata request (MRI-only)

Topic and cluster metadata may be retrieved in the MRI version by querying the Kafka brokers.

require 'hermann'
require 'hermann/discovery/metadata'

c = Hermann::Discovery::Metadata.new( "localhost:9092" )
topic = c.topic("topic")

puts topic.partitions.first

consumers = topic.partitions.map do |partition|
  partition.consumer
end

Testing

To run the integration tests:

• startup your own instance of zookeeper/kafka
• rspec spec/integration/producer_spec.rb

How to convert from using jruby-kafka

• Gemfile
  • remove jruby-kafka
  • add gem "hermann"
  • bundle install
• Jarfile
  • removed unecessary jars from your Jarfile (i.e. kafka, log4j)
  • jar dependencies are automatically included with Hermann
  • jbundle install
• Test out one of the Producer/Consumer examples above