What are publisher confirms in RabbitMQ?

Question

IT Interview Practice · Accepted Answer

**Publisher confirms** are a mechanism where RabbitMQ acknowledges to the producer that it has received (and persisted) a message — ensuring messages aren't lost on the publishing side. They're the producer-side counterpart to consumer acknowledgments.

## The problem: did the message reach the broker?

```text
When a producer publishes a message, by default it doesn't KNOW if RabbitMQ received it:
  → network failure, broker issue → the message could be LOST without the producer knowing
  → for reliability, the producer needs CONFIRMATION that the message was accepted
→ publisher confirms address the PUBLISHING side of reliability
```

## How publisher confirms work

```text
PUBLISHER CONFIRMS → the broker sends an ACK back to the producer for each message:
  → enable confirm mode on the channel
  → the broker ACKs a message once it has taken responsibility (received it; for persistent
    messages on durable queues → once persisted to disk)
  → NACK → the broker couldn't handle the message (the producer can retry)
→ the producer KNOWS each message was accepted (or not) → no silent loss
```

## Using confirms

```text
✓ Wait for confirms (sync) → simple but slower; or handle confirms ASYNCHRONOUSLY (callbacks)
  for throughput (don't block on each)
✓ Batch confirms → confirm batches for better throughput
✓ On NACK/timeout → retry the message (with idempotency awareness)
→ combine with durable queues + persistent messages → reliable end-to-end publishing
```

## Why it matters

Understanding publisher confirms is valuable because they're **essential for publish-side reliability in RabbitMQ**, so it's important knowledge for building reliable messaging.

Publisher confirms address a key reliability gap: by default, when a producer publishes a message, it doesn't know if RabbitMQ actually received it, so a network failure or broker issue could **lose the message without the producer knowing** — a real reliability problem on the publishing side.

Understanding **how publisher confirms work** — the broker sending an **ack back to the producer** for each message once it has taken responsibility (received it, or for persistent messages on durable queues, once persisted to disk), with a **nack** if the broker couldn't handle it (so the producer can retry) — clarifies the mechanism that gives the producer confirmation, preventing silent message loss on publishing.

This is the **producer-side counterpart to consumer acknowledgments** (which protect the consumption side), together providing end-to-end reliability.

Understanding **using confirms** — waiting for confirms synchronously (simple but slower) versus handling them asynchronously via callbacks (for throughput), batching confirms, and retrying on nack/timeout (with idempotency awareness) — reflects practical, efficient use.

Understanding that combining publisher confirms with durable queues and persistent messages provides reliable end-to-end publishing connects confirms to the broader reliability picture (confirms for the publish side, durability for storage, acks for consumption).

Publisher confirms are essential for ensuring messages reliably reach the broker, an important part of reliable messaging often overlooked (people focus on consumer acks but forget publish-side reliability).

Since publisher confirms are essential for publish-side reliability (ensuring messages reach the broker, preventing silent loss) — the producer-side counterpart to consumer acks — and understanding them is important for end-to-end reliable messaging, understanding publisher confirms is valuable, practically-relevant RabbitMQ knowledge — essential for publish-side reliability (preventing silent message loss on publishing), completing the reliability picture alongside consumer acks and durability, and important for building reliable RabbitMQ systems with end-to-end delivery guarantees.

The problem: did the message reach the broker?

How publisher confirms work

Using confirms

Why it matters

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