Table of Contents

• Telekinesis
  • Requirements
  • Installing
  • Producers
  • SyncProducer
  • AsyncProducer
  • Consumers
  • KCL
    • Client State
    • Errors while processing records
    • Checkpoints and INITIAL_POSITION_IN_STREAM
  • Java client logging
• Building
  • Prerequisites
  • Build
• Testing

Telekinesis

Telekinesis is a high-level client for Amazon Kinesis.

The library provides a high-throughput asynchronous producer and wraps the Kinesis Client Library to provide an easy interface for writing consumers.

Requirements

Telekinesis runs on JRuby 1.7.x or later, with at least Java 6.

If you want to build from source, you need to have Apache Maven installed.

Installing

gem install telekinesis

Producers

Telekinesis includes two high-level Producers.

Telekinesis assumes that records are [key, value] pairs of strings. The key must be a string as enforced by Kinesis itself. Keys are used by the service to partition data into shards. Values can be any old blob of data, but for simplicity, Telekinesis expects strings.

Both keys and values should respect any Kinesis limits. and all of the restrictions in the PutRecords API documentation.

SyncProducer

The SyncProducer sends data to Kinesis every time put or put_all is called. These calls will block until the call to Kinesis returns.

require 'telekinesis'

producer = Telekinesis::Producer::SyncProducer.create(
  stream: 'my stream',
  credentials: {
    acess_key_id: 'foo',
    secret_access_key: 'bar'
  }
)

Calls to put send a single record at a time to Kinesis, where calls to put_all can send up to 500 records at a time, which is the Kinesis service limit. If more than 500 records are passed to put_all they're grouped into batches and sent.

NOTE: To send fewer records to Kinesis at a time when using put_all, you can adjust the :send_size parameter in the create method.

Using put_all over put is recommended if you have any way to batch your data. Since Kinesis has an HTTP API and often has high latency, it tends to make sense to try and increase throughput as much as possible by batching data.

# file is an instance of File containing CSV data that looks like:
#
#   "some,very,important,data,with,a,partition_key"
#
lines = file.lines.map do |line|
  key = line.split(/,/).last
  data = line
  [key, data]
end

# One record at a time
lines.each do |key, data|
  producer.put(key, data)
end

# Manually control your batches
lines.each_slice(200) do |batch|
  producer.put_all(batch)
end

# Go hog wild
producer.put_all(lines.to_a)

When something goes wrong and the Kinesis client throws an exception, it bubbles up as a Telekinesis::Aws::KinesisError with the underlying exception accessible as the cause field.

When some of (but maybe not all of) the records passed to put_all cause problems, they're returned as an array of [key, value, error_code, error_message] tuples.

AsyncProducer

The AsyncProducer queues events interally and uses background threads to send data to Kinesis. Data is sent when a batch reaches the Kinesis limit of 500, when the producer's timeout is reached, or when the producer is shut down.

NOTE: You can configure the size at which a batch is sent by passing the :send_size parameter to create. The producer's internal timeout can be set by using the :send_every_ms parameter.

The API for the AsyncProducer is looks similar to the SyncProducer. However, all put and put_all calls return immediately. Both put and put_all return true if the producer enqueued the data for sending later, and false if the producer is not accepting data for any reason. If the producer's internal queue fill up, calls to put and put_all will block.

Since sending (and therefore failures) happen in a different thread, you can provide an AsyncProducer with a failure handler that's called whenever something bad happens.

require 'telekinesis'

class MyFailureHandler
  def on_record_failure(kv_pairs_and_errors)
    items = kv_pairs_and_errors.map do |k, v, code, message|
      maybe_log_error(code, message)
      [k, v]
    end
    save_for_later(items)
  end

  def on_kinesis_error(err, items)
    log_exception(err.cause)
    save_for_later(items)
  end
end

producer = Telekinesis::Producer::AsyncProducer.create(
  stream: 'my stream',
  failure_handler: MyFailureHandler.new,
  send_every_ms: 1500,
  credentials: {
    acess_key_id: 'foo',
    secret_access_key: 'bar'
  }
)

Consumers

KCL

Telekinesis::Consumer::KCL is a wrapper around Amazon's Kinesis Client Library (also called the KCL).

Each KCL instance is part of a group of consumers that make up an application. An application can be running on any number of hosts in any number of processes. Consumers identify themself uniquely within an application by specifying a worker_id.

All of the consumers within an application attempt to distribute work evenly between themselves by coordinating through a DynamoDB table. This coordination ensures that a single consumer processes each shard, and that if one consumer fails for any reason, another consumer can pick up from the point at which it last checkpointed.

This is all part of the official AWS library! Telekinesis just makes it easier to use from JRuby.

Each client has to know how to process all the data it's retreiving from Kinesis. That's done by creating a record processor and telling a KCL how to create a processor when it becomes responsible for a shard.

We highly recommend reading the official docs on implementing the IRecordProcessor interface before you continue.

NOTE: Since initialize is a reserved method, Telekinesis takes care of calling your init method whenever the KCL calls IRecordProcessor's initialize method.

NOTE: Make sure you read the Kinesis Record Processor documentation carefully. Failures, checkpoints, and shutting require some attention. More on that later.

After it is created, a record processor is initialized with the ID of the shard it's processing, and handed an enumerable of Records and a checkpointer (see below) every time the consumer detects new data to process.

Defining and creating a simple processor might look like:

require 'telekinesis'

class MyProcessor
  def init(init_input)
    @shard_id = init_input.shard_id
    $stderr.puts "Started processing #{@shard_id}"
  end

  def process_records(process_records_input)
    process_records_input.records.each do
      |r| puts "key=#{r.partition_key} value=#{String.from_java_bytes(r.data.array)}"
    end
  end

  def shutdown
    $stderr.puts "Shutting down #{@shard_id}"
  end
end

worker = Telekinesis::Consumer::KCL.new(stream: 'some-events', app: 'example') do
  MyProcessor.new
end

worker.run

To make defining record processors easier, Telekinesis comes with a Block processor that lets you use a block to specify your process_records method. Use this if you don't need to do any explicit startup or shutdown in a record processor.

require 'telekinesis'

worker = Telekinesis::Consumer::KCL.new(stream: 'some-events', app: 'example') do
  Telekinesis::Consumer::Block.new do |records, checkpointer, millis_behind|
    records.each {|r| puts "key=#{r.partition_key} value=#{String.from_java_bytes(r.data.array)}" }
  end
end

worker.run

Once you get into building a client application, you'll probably want to know about some of the following advanced tips and tricks.

Client State

Each KCL Application gets its own DynamoDB table that stores all of this state. The :application name is used as the DynamoDB table name, so beware of namespace collisions if you use DynamoDB on its own. Altering or reseting any of this state involves manually altering the application's Dynamo table.

Errors while processing records

When a call to process_records fails, the KCL expects you to handle the failure and try to reprocess. If you let an exception escape, it happily moves on to the next batch of records from Kinesis and will let you checkpoint further on down the road.

From the official docs:

The KCL relies on processRecords to handle any exceptions that arise from processing the data records. If an exception is thrown from processRecords, the KCL skips over the data records that were passed prior to the exception; that is, these records are not re-sent to the record processor that threw the exception or to any other record processor in the application.

The moral of the story is that you should be absolutely sure you catch any exceptions that get thrown in your process_records implementation. If you don't, you can (silently) drop data on the floor.

If something terrible happens and you can't attempt to re-read the list of records and re-do whatever work you needed to do in process records, we've been advised by the Kinesis team that killing the entire JVM that's running the worker is the safest thing to do. On restart, the consumer (or another consumer in the application group) will pick up the orphaned shards and attempt to restart from the last available checkpoint.

Checkpoints and INITIAL_POSITION_IN_STREAM

The second object passed to process_records is a checkpointer. This can be used to checkpoint all records that have been passed to the processor so far (by just calling checkpointer.checkpoint) or up to a particular sequence number (by calling checkpointer.checkpoint(record.sequence_number)).

While a KCL consumer can be initialized with an :initial_position_in_stream option, any existing checkpoint for a shard will take precedent over that value. Furthermore, any existing STATE in DynamoDB will take precedent, so if you start a consumer with initial_position_in_stream: 'LATEST' and then restart with initial_position_in_stream: 'TRIM_HORIZON' you still end up starting from LATEST.

Java client logging

The AWS Java SDK can be extremely noisy and hard to control, since it logs through java.util.logging.

Telekinesis comes with a shim that can silence all of that logging or redirect it to a Ruby Logger of your choice. This isn't fine-grained control - you're capturing or disabling ALL logging from any Java dependency that uses java.util.logging - so use it with care.

To entirely disable logging:

Telekinesis::Logging.disable_java_logging

To capture all logging and send it through a Ruby logger:

Telekinesis::Logging.capture_java_logging(Logger.new($stderr))

---

Building

Prerequisites

• JRuby 1.7.9 or later.
• Apache Maven

Build

Install JRuby 1.7.9 or later, for example with rbenv you would:

$ rbenv install jruby-1.7.9

Install Bundler and required Gems.

$ gem install bundler
$ bundle install

Install Apache Maven.

On Ubuntu or related use:

$ sudo apt-get install maven

The easiest method on OSX is via brew.

$ sudo brew install maven

Ensure JAVA_HOME is set on OSX.

Ensure your JAVA_HOME environment variable is set. In Bash for example add the following to ~/.bash_profile.

export JAVA_HOME=$(/usr/libexec/java_home)

Then run:

$ source ~/.bash_profile

Build the Java shim and jar.

$ rake ext:build

The rake ext:build task builds the Java shim and packages all of the required Java classes into a single jar. Since bytecode is portable, the JAR is shipped with the built gem.

Build the Gem.

Use the rake gem:build task to build the complete gem, uberjar and all.

$ rake gem:build

Testing

Telekinesis comes with a small set of unit tests. Run those with plain ol' rake test.

NOTE: The Java extension must be built and installed before you can run unit tests.

Integration tests coming soon.