Day 9Level 1 — Core Mental Models
Design Brief: Payment System — Idempotency & Delivery Guarantees
Learn: 45 minMap: 35 minDesign: 70 min
Core Concepts (5)
- 1.Payments require: idempotency, audit trail, reconciliation, exactly-once settlement
- 2.Outbox pattern ensures DB + message atomicity for payment events
- 3.Reconciliation jobs catch drift between systems
- 4.PCI DSS constraints shape architecture — tokenization, encryption, scope reduction
- 5.Webhook idempotency: provider retries must not double-charge
Map to Your Experience
You're building a payment service. A user clicks "Pay" twice rapidly. Trace what happens in your system. Where could double-charge occur?
Design Brief: Payment System — Idempotency & Reconciliation
Requirements
- •Process payments with idempotency keys
- •Handle provider webhooks idempotently
- •Support refunds and partial captures
- •Daily reconciliation with provider statements
- •Audit trail for every state transition
Constraints
- •PCI DSS SAQ-A compliance (tokenization only)
- •p99 latency < 2s for payment initiation
- •Zero data loss — all events persisted
- •Provider API: at-least-once webhook delivery
Must Cover
idempotency-keysduplicate-handlingdelivery-guaranteesdata-correctnessreconciliation
Trade-off Axis
simplicity vs correctness
Referenced Patterns
Competencies Advanced
data state → L3reliability ops → L3security compliance → L2
Ready to Design?
Open this brief in the Design Studio. Your constraints, requirements, and patterns will be pre-filled. Create a Design Record and get AI critique.
Open in Studio →