Auto Ack

Overview

Auto-ack is the fire-and-forget receive mode for queues: the broker marks a message as consumed the instant it hands it to your client, instead of waiting for your code to settle it. Reach for it when the work is idempotent, low-value, or cheap to lose — a metrics ping, a cache warm, a best-effort notification — and you'd rather not carry the bookkeeping of explicit acknowledgment for every message.

It works by setting auto_ack: true on the options passed to KubeMQ.Client.poll_queue/2. With it enabled, delivery and acknowledgment happen as one atomic step on the broker side, so there's no separate PollResponse.ack_all/1 call and no in-flight "pending" state for the message to sit in.

Gotchas: if your consumer crashes after poll_queue/2 returns but before it finishes processing, that message is gone for good — auto-ack gives you no chance to nack or requeue it, unlike Ack & Reject. It's an at-most-once model, so never use it for messages where losing one silently would matter. And because acknowledgment happens on delivery, max_items and wait_timeout are your only throttles — there's no visibility-timeout window to tune.

Prerequisites

• KubeMQ server running on localhost:50000
• Elixir SDK installed ({:kubemq, "~> 1.0"} in mix.exs)

Code

channel = "elixir-queues.auto-ack"
{:ok, client} = KubeMQ.Client.start_link(address: "localhost:50000", client_id: "elixir-qs-autoack")

for i <- 1..3 do
  {:ok, _} = KubeMQ.Client.send_queue_message(client,
    KubeMQ.QueueMessage.new(channel: channel, body: "Auto-ack msg #{i}"))
end

IO.puts("Sent 3 messages")

case KubeMQ.Client.poll_queue(client,
       channel: channel,
       max_items: 10,
       wait_timeout: 5_000,
       auto_ack: true
     ) do
  {:ok, poll} ->
    IO.puts("Received #{length(poll.messages)} messages (auto-acked)")

    Enum.each(poll.messages, fn msg ->
      IO.puts("  #{msg.body}")
    end)

    IO.puts("No manual ack needed — server handled it")

  {:error, err} ->
    IO.puts("Poll failed: #{err.message}")
end

case KubeMQ.Client.receive_queue_messages(client, channel,
       max_messages: 10,
       wait_timeout: 2_000
     ) do
  {:ok, result} ->
    IO.puts("Remaining messages: #{result.messages_received}")

  {:error, _} ->
    IO.puts("Queue empty (confirmed)")
end

KubeMQ.Client.close(client)

How It Works

• auto_ack: true tells the server to acknowledge messages immediately when delivered
• No manual PollResponse.ack_all/1 call is needed
• Best for scenarios where message processing is guaranteed to succeed

Related

• Ack/Reject
• Stream Receive