What is the difference between an SQS standard and FIFO queue?
AWS · Advanced level
Answer
SQS Standard offers high throughput with at-least-once delivery and best-effort ordering. FIFO preserves ordering within message groups and supports deduplication, but requires careful design for throughput and parallelism.
Technical explanation
FIFO ordering is per message group, so message group design determines parallelism.
Messaging services decouple producers and consumers, but the reliability model depends on ordering, retries, DLQs, idempotency, batching, and backpressure.
At-least-once delivery means consumers must safely handle duplicate messages unless the business can tolerate duplicates.
Monitor queue depth, age of oldest message, DLQ count, consumer errors, throttles, and downstream saturation.
Hands-on example
1. Create a small producer and consumer using the relevant service - SQS, SNS, or EventBridge.
2. Add retry, DLQ, visibility timeout or event rule configuration, and idempotency key handling.
3. Inject duplicate messages, consumer failure, and downstream throttling to observe retry and backpressure behavior.
4. Alarm on age, DLQ count, failed deliveries, throttles, and consumer error rate.
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