Elsa

Description

Elsa is a full-featured Kafka library written in Elixir and extending the :brod library with additional support from the :kafka_protocol Erlang libraries to provide capabilities not available in :brod.

Elsa has the following goals:

Run entirely as a library (only start processes explicitly listed in your supervision tree)
Draw none of its configuration from the calling application's app env
Minimize and isolate failures in the broker/consumer interaction

As Elsa draws from the Brod library (named for Kafka friend and biographer Max Brod), it is named for Elsa Taussig, Brod's wife.

Installation

The package can be installed by adding elsa to your list of dependencies in mix.exs:

def deps do
  [
    {:elsa, "~> 1.0.0-rc.2"}
  ]
end

Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/elsa.

Usage

To use Elsa in your application, configure the start of the top-level supervisor to run and pass it the necessary arguments as a keyword list. Below is an example of the arguments as they might be defined in the application environment config.exs or runtime.exs files.

config :my_app, :elsa,
  endpoints: [localhost: 9092],
  name: :myapp_elsa,
  producer: [
    topic: "outgoing-stream"
  ],
  group_consumer: [
    group: "data-stream-group",
    topics: ["incoming-streaming"],
    handler: MyApp.MessageHandler,
    handler_init_args: %{},
    config: [
      begin_offset: :earliest
    ]
  ],
  consumer: [
    topic: "incoming-stream",
    partition: 0,
    begin_offset: :earliest,
    handler: MyApp.MessageHandler
  ]

Note that each Elsa supervisor tree requires a single list of Kafka brokers and a single name. Beyond that, defining consumer groups or producers is optional (although defining neither will result in a relatively useless Elsa supervisor and registry).

Producers may be a single producer or a list of producers, differentiated by their topic, therefore Elsa allows a one-to-many association of supervision tree to producers.

Consumers and consumer groups, in contrast, have a one-to-one relationship to an Elsa supervision tree, therefore you cannot define a nested list of consumer or group_consumer keyword arguments within your Elsa configuration.

Example

You can find an example of configuring and using Elsa here.

Testing

Elsa uses the standard ExUnit testing library for unit testing. For integration testing interactions with Kafka, it uses the divo library. Run tests with the command mix test.integration.

bbalser / elsa