principle-cost-awarenesslisted

# Cost Awareness Cost bugs are design bugs. They are cheapest to fix before the first dollar is spent. This skill teaches design-time discipline — choosing the right tier, topology, and access pattern — not post-billing cost reduction tactics. ## FinOps Mindset Cost is a feature requirement, not an afterthought. Treat budget the same way you treat latency and availability SLOs. - Name a cost budget alongside the performance budget at design time. "Under $X/month at N req/s" is a testable acceptance criterion. - Cloud bills are emergent: small per-request charges multiply by request volume, retention windows, and replica count in ways that are invisible in local testing. - Assign cost ownership to the team that controls the resource. Shared cost pools obscure accountability and slow optimization. - Unit economics clarify decisions: cost-per-request, cost-per-GB-stored, cost-per-active-user. Derive these early; revisit when scale changes by 10×. ## Egress and Data Movement Egress is the most common billing surprise — data that moves costs more than data that sits still. - Intra-AZ traffic is typically free; cross-AZ traffic carries per-GB charges; cross-region is more expensive; egress out of a cloud to another cloud is most expensive (inbound/ingress is typically free on most providers). Map outbound data flows against this hierarchy at design time. - Chatty microservice calls that exchange large payloads inflate egress costs non-linearly as request rates grow. Prefer coa