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On a composite ingest workload (~8k ordered TPS, 1 KB payloads), staying on SQS FIFO without high-throughput mode capped effective throughput near 300 TPS/API and modeled queue backlog cost near $95/mo before ops time — enabling high-throughput FIFO or switching to Kinesis on-demand changed the ceiling, not the consumer code.
On a composite B2B order API (~2.4k RPS peak, 24 ECS tasks on Aurora), running the scaling ladder in order — RDS Proxy, read-replica routing, ElastiCache, then SQS offload — moved modeled p99 from 1,840 ms to 72 ms before any microservice split.
SQS charges $0.40 per million standard requests and $0.50 per million FIFO requests, but a single 256 KB message counts as four requests under the 64 KB rule. Short polling on idle queues silently quadruples the bill. Cross-region data transfer adds a line many teams never count.
Standard SQS queues sustain nearly unlimited throughput per queue (AWS-documented pattern) while FIFO caps at 300 TPS per API batch without high-throughput mode—your May 2026 architecture review should start from those numbers, not from Kafka slogans.
API Gateway REST integrations still max out at 29 seconds—if your Lambda keeps retrying a 35-second partner HTTP call without a bounded circuit, you burn capacity and duplicate side effects instead of failing fast.