AWS ECS + Fargate Architecture

ALB: TLS + routing + health checks
ECS API Service: NestJS HTTP app
ECS Worker Service: SQS consumers for fulfillment
Aurora PostgreSQL: orders, holds, tickets (transactions/locks)
ElastiCache Redis: cache + burst protection + distributed locks (optional)
SQS + DLQ: resilient background processing
S3: ticket PDFs, assets, exports
SES: ticket + receipt emails

This architecture favors AWS-managed services to reduce operational burden while keeping strong correctness guarantees for ticketing.