Kaffe.Consumer (Kaffe v1.28.0)

Consume messages from Kafka and pass to a given local module.

See start_link/4 for details on how to start a Consumer process.

As messages are consumed from Kafka they will be sent to your handle_message/1 (sync) or handle_message/2 (async) functions for processing in your system. Those functions must return :ok.

Kaffe.Consumer commits offsets to Kafka which is very reliable but not immediate. If your application restarts then it's highly likely you'll reconsume some messages, especially for a quickly moving topic. Be ready!

Summary

Types

message()

Functions

ack(pid, map)

Acknowledge the Kafka message as processed.

handle_message(topic, partition, msg, state)

Call the message handler with the restructured Kafka message.

init(consumer_group, list)

Initialize the consumer loop.

kafka_message(args \\ [])

kafka_message(record, args)

start_consumer_client(config)

start_link(config_key)

Start a Kafka consumer

Types

message()

@type message() :: %{
  key: binary(),
  value: binary(),
  topic: binary(),
  offset: non_neg_integer(),
  partition: non_neg_integer(),
  ts: non_neg_integer(),
  ts_type: :undefined | :create | :append,
  headers: list()
}

Functions

ack(pid, map)

Acknowledge the Kafka message as processed.

pid - the pid your handle_message/2 function was given as the first argument
message - the Kafka message your handle_message/2 function was given as the second argument

Kaffe.Consumer.ack(pid, message)

handle_message(topic, partition, msg, state)

Call the message handler with the restructured Kafka message.

Kafka messages come from brod as an Erlang record. To make processing simpler for clients we convert that to an Elixir map. Since the consumer can subscribe to multiple topics with multiple partitions we also add the topic and partition as additional fields.

After compiling the Kafka message your message handler module's handle_message function will be called.

If async is false:

Your message handler module's handle_message/1 function will be called with the message
The Consumer will block and wait for your handle_message function to complete and then automatically acknowledge the message as processed.

If async is true:

Your message handler module's handle_message/2 function will be called with the pid of the running Consumer process and the message.
Message intake on the Consumer will not wait for your handle_message/2 to complete and will not automatically acknowledge the message as processed.
Once you've processed the message you will need to call Kaffe.Consumer.ack/2 with the pid and message.

init(consumer_group, list)

Initialize the consumer loop.

kafka_message(args \\ [])

(macro)

kafka_message(record, args)

(macro)

start_consumer_client(config)

start_link(config_key)

Start a Kafka consumer

The consumer pulls in values from the Kaffe consumer configuration. See more details at Kaffe.Config.Consumer.