amazon-api-gateway

After Cognito multi-Region replication (June 2026), a B2B API platform (~18k RPS peak) cut auth-related 5xx during a regional drill from 4.2% → 0.1% — but a missing WAF rate rule still let a scraper burn $1.8k in a weekend.

For a mid-market retailer (~2.4M SKUs, checkout p95 1.9s → 420ms), DynamoDB cart + Step Functions checkout + conditional inventory cuts held 2.1k checkout RPS — after a cache-as-inventory mistake oversold 380 units in 12 minutes.