When to Use a Dead-Letter Queue?
A dead-letter queue (DLQ) is a backup queue for storing messages that repeatedly fail to process, ensuring they don’t block or overload the main queue.
When to Use
Use a DLQ when messages are unprocessable due to issues like invalid data, expired events, or service timeouts. It helps isolate failures without impacting overall system throughput.
Example
In a payment system, if a message fails due to a corrupted payload, it’s moved to a DLQ so valid transactions can keep flowing.
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Why Is It Important
Dead-letter queues improve system reliability by preventing endless retries, preserving failed messages for debugging, and ensuring smooth operation of the main queue.
Interview Tips
Be ready to define DLQs, explain when they’re used, and provide a real-world example.
Highlight that they improve fault tolerance but need monitoring.
Trade-offs
DLQs add resilience but also increase complexity, storage costs, and require monitoring. They are essential in critical systems but may be unnecessary for simple apps.
Pitfalls
Common mistakes include leaving DLQs unmonitored, misconfiguring retry thresholds, or assuming DLQs solve errors automatically—they only store failed messages.
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