American Express uses a cell-based architecture to isolate failures and maintain low-latency, predictable performance in its core payments platform. Each cell contains its own microservices and data, while a Global Transaction Router directs transactions to the cell with the required state. Asynchronous replication and strict ingress/egress boundaries keep cells independent and limit failure blast radius.

• Amex isolates payment processing into self-sufficient cells so failures stay contained and don't ripple across the whole system.
• Static reference data (currency rates, merchant codes) is pre-pushed to every cell, avoiding fallback lookups that would slow transactions.
• A Global Transaction Router directs each transaction to the cell holding authoritative state, with async replication kept outside the critical path to avoid latency.
• All inter-cell communication is forced through the router/payment mesh, enforcing strict boundaries so transactions can't bypass a failing cell.