Case Study: Top-10 Bank achieves mainframe-grade cloud ledger reliability with FaunaDB

Moving critical ledger applications from mainframes to the cloud

Major Bank, a top‑ten bank specializing in credit cards, auto loans and consumer banking, set out to replatform legacy systems to AWS and move its mission‑critical distributed auto‑loan ledger off mainframes. Relational databases couldn’t scale in the cloud and early NoSQL systems lacked the strong consistency and multi‑region guarantees required, so Major Bank selected Fauna (FaunaDB) to provide mainframe‑grade availability, strongly consistent multi‑region replication, and a flexible document model with familiar relational features.

Fauna implemented FaunaDB as the cloud database for the auto‑loan ledger, delivering horizontal scalability, high availability, ACID transactions across regions, indexes/joins, and fine‑grained security and audit capabilities. As a result, the ledger now runs in AWS with mainframe‑level reliability—handling daily balance and interest calculations for millions of auto‑loan customers—while reducing operational complexity and cost; Major Bank is now expanding Fauna to modernize other core systems such as its credit‑card ledger.