# Revision and Interview Questions — RabbitMQ

Source: https://www.skillbyai.com/en/rabbitmq/p-revision

> Recall RabbitMQ concepts quickly for exams and interviews.

## Cheat sheet

**Model**: producer → exchange → binding → queue → consumer; vhosts isolate; connections are long-lived, channels multiplex. **Exchanges**: default (queue name), direct (exact key), fanout (all), topic (`*` one word, `#` zero or more), headers (`x-match` all/any); unroutable messages are dropped unless mandatory or an alternate exchange is used. **Patterns**: work queues, pub/sub, routing, RPC with `reply_to` + `correlation_id` and direct reply-to. **Consuming**: manual acks; nack/reject with or without requeue; prefetch for fairness versus throughput; at-least-once means idempotent consumers keyed by `message_id`. **Publishing**: confirms, mandatory/returns, persistent messages on durable queues, outbox for business events. **Failures**: DLX on reject, TTL expiry, length overflow or delivery limit; TTL retry queues; parking lot. **Queue types**: classic (single node, transient or temporary data), quorum (Raft, majority-confirmed, delivery limit; the default for safety), streams (non-destructive log, offsets, replay, super streams); mirrored classic queues removed in 4.0. **Ops**: 3-node clusters across zones, Khepri metadata, memory and disk alarms block publishers, Prometheus metrics, least-privilege vhost permissions, TLS, topology as code.

## Common interview questions

Answer each with a mechanism and an example.

```text
1. Walk through how a message travels from producer to consumer in RabbitMQ.
2. Compare direct, fanout, topic and headers exchanges.
3. What is the difference between auto-ack and manual ack?
4. What does prefetch do, and how would you choose a value?
5. How do publisher confirms differ from consumer acknowledgements?
6. What makes a message survive a broker restart?
7. How do dead-letter exchanges work, and how would you build delayed retries?
8. Classic vs quorum queues vs streams: when would you use each?
9. How do you make consumers safe against duplicate deliveries?
10. When would you choose RabbitMQ over Kafka, and vice versa?
```

## Explain the guarantees end to end

A strong answer traces a message's safety at each hop: outbox to publisher, confirms to broker, quorum replication inside the broker, manual acks and idempotency at the consumer.

**Quiz:** Which combination gives the strongest guarantee that a published order event is not lost and is processed once in effect?

- [ ] Auto-ack consumers and transient messages
- [ ] Fanout exchange with exclusive queues
- [ ] Classic queues with no confirms
- [x] Outbox publishing with confirms, persistent messages on a quorum queue, and idempotent consumers with manual acks

*Answer:* Outbox publishing with confirms, persistent messages on a quorum queue, and idempotent consumers with manual acks. Each hop needs its own safeguard: confirms, replication, manual acks and deduplication.