Engineers almost always misjudge cloud costs. They predict EC2·RDS "compute" well, but miss data transfer and storage tier costs flowing between services. Then bills arrive showing NAT Gateway costing more than RDS, or Cross-AZ traffic consuming 20%+ of total spend. This "hidden cost" is what SAP-C02 relentlessly probes — everyone optimizes compute, but architecting cost into data flow differentiates true architects.
Today we dissect three major cost drains: S3 storage tier economics, AWS network billing's directional structure, and NAT Gateway's double-charging trap, examining their internals and cost-reduction vs anti-patterns.