American Express redesigned their payment platform using cell-based architecture—independent, self-contained processing units that isolate failures and keep transactions moving even when parts of the system fail. The system routes transactions deterministically to cells holding the right data, avoiding cross-cell dependencies during payment processing.

• Cells are failure boundaries, not functional units: each cell contains everything needed to process a transaction (microservices, databases, DNS) so problems stay contained and don't cascade across the platform.
• Data strategy varies by change frequency: immutable and semi-static data gets pushed to all cells before transactions arrive, while dynamic data triggers deterministic routing to send transactions to cells holding current state.
• The Global Transaction Router enforces cell isolation by being the only path between cells and external systems, kept deliberately simple to avoid becoming a bottleneck—it just parses messages and routes, leaving all business logic to the cells.