Design a bank account service

Q: Design a bank account service

This is a System Design interview question from Coinbase for Software Engineer roles. View the full question and solution on PracHub.

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Question

System Design: Bank Account Service for a Fintech App

Context

Design a backend service that manages customer bank accounts with robust financial correctness, auditability, and scalability. The service must support core banking operations, enforce balance rules, maintain an immutable double-entry ledger, and provide strong consistency guarantees.

Requirements

Core features
- Create accounts.
- Deposits, withdrawals, and transfers between accounts.
- Real-time balance queries.
- Monthly statements.
Financial correctness
- Enforce balance and overdraft rules.
- Immutable double-entry ledger.
- Transactional integrity for cross-account transfers (all-or-nothing).
API behavior
- Idempotent APIs.
- Concurrency and race-condition handling.
Scale and reliability
- Multi-region scaling strategy preserving consistency and auditability.
- Failure handling and operational monitoring.
Deliverables
- Data model.
- Core APIs (with idempotency approach).
- Transaction flows.
- Failure handling plan.
- Monitoring and observability.

Design a bank account service

System Design: Bank Account Service for a Fintech App

Context

Requirements

Solution (Locked)

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