Module: Karafka::Processing::Strategies::Dlq

Includes:
Default
Included in:
DlqMom
Defined in:
lib/karafka/processing/strategies/dlq.rb

Overview

When using dead letter queue, processing won’t stop after defined number of retries upon encountering non-critical errors but the messages that error will be moved to a separate topic with their payload and metadata, so they can be handled differently.

Constant Summary collapse

FEATURES =

Apply strategy when only dead letter queue is turned on

%i[
  dead_letter_queue
].freeze

Instance Method Summary collapse

Methods included from Default

#commit_offsets, #commit_offsets!, #handle_before_consume, #handle_before_enqueue, #handle_consume, #handle_idle, #handle_revoked, #handle_shutdown, #mark_as_consumed, #mark_as_consumed!

Methods included from Base

#handle_before_consume, #handle_before_enqueue, #handle_consume, #handle_idle, #handle_revoked, #handle_shutdown

Instance Method Details

#dispatch_to_dlq(skippable_message) ⇒ Object

Moves the broken message into a separate queue defined via the settings

Parameters:



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# File 'lib/karafka/processing/strategies/dlq.rb', line 72

def dispatch_to_dlq(skippable_message)
  producer.produce_async(
    topic: topic.dead_letter_queue.topic,
    payload: skippable_message.raw_payload
  )

  # Notify about dispatch on the events bus
  Karafka.monitor.instrument(
    'dead_letter_queue.dispatched',
    caller: self,
    message: skippable_message
  )
end

#find_skippable_message ⇒ Array<Karafka::Messages::Message, Boolean>

Finds the message may want to skip (all, starting from first)

Returns:

  • (Array<Karafka::Messages::Message, Boolean>) —

    message we may want to skip and information if this message was from marked offset or figured out via mom flow



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# File 'lib/karafka/processing/strategies/dlq.rb', line 56

def find_skippable_message
  skippable_message = messages.find do |msg|
    coordinator.marked? && msg.offset == coordinator.seek_offset
  end

  # If we don't have the message matching the last comitted offset, it means that
  # user operates with manual offsets and we're beyond the batch in which things
  # broke for the first time. Then we skip the first (as no markings) and we
  # move on one by one.
  skippable_message ? [skippable_message, true] : [messages.first, false]
end

#handle_after_consume ⇒ Object

When manual offset management is on, we do not mark anything as consumed automatically and we rely on the user to figure things out



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# File 'lib/karafka/processing/strategies/dlq.rb', line 19

def handle_after_consume
  return if revoked?

  if coordinator.success?
    coordinator.pause_tracker.reset

    return if coordinator.manual_pause?

    mark_as_consumed(messages.last)
  elsif coordinator.pause_tracker.attempt <= topic.dead_letter_queue.max_retries
    retry_after_pause
  # If we've reached number of retries that we could, we need to skip the first message
  # that was not marked as consumed, pause and continue, while also moving this message
  # to the dead topic
  else
    # We reset the pause to indicate we will now consider it as "ok".
    coordinator.pause_tracker.reset

    skippable_message, = find_skippable_message

    # Send skippable message to the dql topic
    dispatch_to_dlq(skippable_message)

    # We mark the broken message as consumed and move on
    mark_as_consumed(skippable_message)

    return if revoked?

    # We pause to backoff once just in case.
    pause(coordinator.seek_offset, nil, false)
  end
end