How do you process queue messages safely in the cloud?

Summary

Assume at-least-once delivery: make consumers idempotent, set the visibility timeout longer than processing time (or extend it), use dead-letter queues after a few attempts and alert on them, batch where possible and handle partial batch failures. Use FIFO queues or ordering keys only when order matters.

Longer Answer

SQS default visibility timeout is 30 seconds; messages not deleted in time reappear. Pub/Sub has ack deadlines and Service Bus has lock durations with the same semantics.

Key Points

• At-least-once: idempotent consumers.
• Visibility timeout > processing time.
• Dead-letter queues with alerts.
• Ordering only when needed.

Deep dive: Cloud Computing Tutorial: Queues, Topics and Events

What interviewers look for

Duplicate handling and failure paths.