System Design: Global Bank with Multi-Region Data Consistency

A digital bank operates in multiple geographic regions (e.g., EU, US, APAC). Users can log in and perform operations (balance checks, transfers, card payments) from anywhere.

Prompt

Design a data architecture that keeps customer/account data consistent across regions.

Requirements

• High availability and low latency for reads (users worldwide).
• Correctness for money movement (no double-spend).
• Tolerate regional failures and network partitions.
• Clear consistency model: what must be strongly consistent vs what can be eventually consistent.

Discussion Points

• Replication strategy (sync/async, leader-based vs multi-leader).
• How to handle cross-region writes (especially transfers).
• Conflict resolution and idempotency.
• Operational concerns: recovery, reconciliation, auditing, observability.