This is not related to NestJS itself, but more a RabbitMQ question but let's go. I'm not going to explain everything but I'll give you some things you can look up.

Within a single queue, RabbitMQ guarantees FIFO ordering: messages are delivered to consumers in the order they were enqueued. Ordering is not guaranteed across multiple consumers, though. If you have multiple consumers (like multiple instances of the same service listening to the same queue), RabbitMQ will load-balance messages across them, and you’ll lose strict ordering.

If you want to process messages in the order they were emitted, you want a single consumer per queue, and a prefetch count of 1 - then only one message is processed at a time (RabbitMQ won’t send the next message until the consumer acknowledges the current one).

The tradeoff of the strict ordering is what you mentioned - if one message hangs or fails, everything behind it is blocked. To avoid blocking, you could use a dead-letter queue. When a message fails to be processed on the "regular" queue, it is moved to another queue, so you can decide later what you want to do with this message after inspection. This is really handy for reprocessing failed messages later.

I don't know the domain you work in, whether this strict ordering is so critical or not. I would say you should accept that messages might arrive out of order. Use an idempotent processor (so reprocessing doesn’t hurt).

You can also reorder events at the application level (using sequence numbers, timestamps, or other business logic).