A Kafka client for Erlang and Elixir

Copyright (c) 2014, 2015 Finexkap, 2015 G-Corp, 2015, 2016 BotsUnit

Version: 2.0.0

Authors: Gregoire Lejeune (gregoire.lejeune@finexkap.com), Gregoire Lejeune (greg@g-corp.io), Gregoire Lejeune (gregoire.lejeune@botsunit.com).

Version 2.0.0 cause changes in the following APIs :

• kafe:start_consumer/3

• kafe:fetch/3

Kafe has been tested with Kafka 0.9 and 0.10

You can also use it with Kafka 0.8 but kafe_consumer is not compatible with this version.

Links

• Apache Kafka
• Apache Kafka Protocol

Configuration

use 0 with Kafka >= 0.8 < 0.9 ; 1 with Kafka >= 0.9 < 0.10 ; 2 with Kafka >= 0.10

Example :

[
  {kafe, [
    {brokers, [
      {"localhost", 9092},
      {"localhost", 9093},
      {"localhost", 9094}
    ]},
    {pool_size, 1},
    {chunk_pool_size, 2},
    {brokers_update_frequency, 10000},
    {client_id, <<"kafe">>},
    {api_version, 1},
    {correlation_id, 0},
    {socket, [
      {sndbuf, 4194304},
      {recbuf, 4194304},
      {buffer, 4194304}
    ]},
  ]}
]

Kafe use lager ; see also how to configure it.

Create a consumer

Using a function

To create a consumer, create a function with 6 parameters :

-module(my_consumer).

-export([consume/6]).

consume(CommitID, Topic, Partition, Offset, Key, Value) ->
  % Do something with Topic/Partition/Offset/Key/Value
  ok.

The consume function must return ok if the message was treated, or {error, term()} on error.

Then start a new consumer :

...
kafe:start(),
...
kafe:start_consumer(my_group, fun my_consumer:consume/6, Options),
...

See kafe:start_consumer/3 for the available Options.

In the consume function, if you didn't start the consumer in autocommit mode (using before_processing | after_processing in the commit options), you need to commit manually when you have finished to treat the message. To do so, use kafe_consumer:commit/4.

When you are done with your consumer, stop it :

...
kafe:stop_consumer(my_group),
...

Using the kafe_consumer_subscriber behaviour

-module(my_consumer).
-behaviour(kafe_consumer_subscriber).

-export([init/4, handle_message/2]).
-include_lib("kafe/include/kafe_consumer.hrl").

-record(state, {
               }).

init(Group, Topic, Partition, Args) ->
  % Do something with Group, Topic, Partition, Args
  {ok, #state{}}.

handle_message(Message, State) ->
  % Do something with Message
  % And update your State (if needed)
  {ok, NewState}.

Then start a new consumer :

...
kafe:start().
...
kafe:start_consumer(my_group, {my_consumer, Args}, Options).
% Or
kafe:start_consumer(my_group, my_consumer, Options).
...

To commit a message (if you need to), use kafe_consumer:commit/4.

Using with Elixir

Elixir' users can use Kafe and Kafe.Consumer instead of :kafe and :kafe_consumer.

defmodule My.Consumer do
  def consume(commit_id, topic, partition, offset, key, value) do
    # Do something with topic/partition/offset/key/value
    :ok
  end
end

defmodule My.Consumer.Subscriber do
  behaviour Kafe.Consumer.Subscriber

  def init(group, topic, partition, args) do
    % Do something with group/topic/partition/args
    % and create the state
    {:ok, state}
  end

  def handle_message(message, state) do
    % Do something with message (record Kafe.Records.message or
    % function Kafe.Consumer.Subscriber.message/2)
    % and update (or not)the state
    {:ok, new_state}
  end
end

...
Kafe.start()
...
Kafe.start_consumer(:my_group, &My.Consumer.consume/6, options)
# or
Kafe.start_consumer(:my_group, {My.Consumer.Subscriber, args}, options)
# or
Kafe.start_consumer(:my_group, My.Consumer.Subscriber, options)
...
Kafe.stop_consumer(:my_group)
...

Metrics

You can enable metrics by adding a metrics module in your configuration :

{metrics, [
  {metrics_mod, metrics_folsom}
]}

You can choose between Folsom ({metrics_mod, metrics_folsom}), Exometer ({metrics_mod, metrics_exometer}) or Grapherl ({metrics_mod, metrics_grapherl}).

Be sure that's Folsom, Exometer or Grapherl is started before starting Kafe.

application:ensure_all_started(folsom).
application:ensure_all_started(kafe).

Metrics are disabled by default.

Kafe offers the following metrics :

You can add a prefix to all metrics by adding a metrics_prefix in the metrics configuration :

{metrics, [
  {metrics_mod, metrics_folsom},
  {metrics_prefix, my_bot}
]}

Build

Kafe use rebar3. So, you can use :

• ./rebar3 compile to compile Kafe.

• ./rebar3 eunit to run tests.

• ./rebar3 edoc to build documentation.

• ./rebar3 elixir generate_mix to generate mix.exs file.

• ./rebar3 elixir generate_lib to generate Elixir bindings.

API Documentation

See documentation

Contributing

1. Fork it ( https://github.com/botsunit/kafe/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Licence

kafe is available for use under the following license, commonly known as the 3-clause (or "modified") BSD license:

Copyright (c) 2014, 2015 Finexkap<br /> Copyright (c) 2015, G-Corp<br /> Copyright (c) 2015, 2016 BotsUnit<br />

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:* Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
• The name of the author may not be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR AS IS AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

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