The most expensive AWS bills do not come from large-scale systems under heavy load. They come from small systems with invisible failure modes: infinite retry loops, misconfigured queues, forgotten resources, and traffic patterns nobody anticipated.
A technical guide to hybrid compute architectures that combine EC2, Lambda, Fargate, and Step Functions — with worked cost calculations, SQS buffering patterns, and decision frameworks based on invocation pattern rather than unit cost.
Step Functions is the AWS service most teams under-use until they need it badly. Patterns for sequential pipelines, parallel fan-out, error handling, human approval workflows, and the cost optimisations that keep state-transition bills predictable.
