Amazon SQS
Standard vs FIFO Queues
Choose between massive-throughput best-effort (Standard) and ordered exactly-once (FIFO).
Amazon SQS offers two queue types with different guarantees. Standard queues give nearly unlimited throughput and at-least-once delivery, but only best-effort ordering — messages can arrive out of order and occasionally be delivered more than once. They are the default for most decoupling and fan-in workloads.
Standard is a huge open mailroom where letters get processed fast but may be handled slightly out of order or copied twice. FIFO is a single-file ticket line per customer: strict order, and each ticket served exactly once.
Key Concepts
1
FIFO queues guarantee strict ordering within a message group and exactly-once processing (deduplication), at the cost of much lower throughput (a few thousand messages/sec, higher with batching and high-throughput mode). Ordering is per MessageGroupId, so unrelated groups still process in parallel — similar in spirit to Kafka partition keys.
2
The decision is about whether order and dedup matter: if your consumers are idempotent and order is irrelevant, Standard is simpler and scales infinitely; if you process sequential commands per entity, FIFO is worth the throughput trade-off.