Building Resilient Payment Gateways: Lessons from Processing $10 Billion in Transactions
Processing payments at scale is one of the hardest problems in distributed systems. Every transaction must be exactly-once, the system must be available 99.999% of the time, and reconciliation must be perfect. A payment gateway that processes 100 million transactions per month cannot afford to lose a single transaction or double-charge a single customer. We have built payment gateway infrastructure for fintechs processing over $10 billion in annual transaction volume. The architecture decisions that matter are not about speed — they are about correctness, idempotency, and the ability to recover from partial failures without losing money. ...