Design a scalable banking system
Overview
This question evaluates system design skills focused on distributed systems architecture, transactional integrity, strong consistency models, security and authentication, external payment and ATM integrations, data modeling, API design, concurrency control, and operational monitoring for financial platforms.
Capital One
Sep 6, 2025, 12:00 AM
Software Engineer
Onsite
System Design
0
0
System Design: Online Banking Platform
Context
Design an online banking platform (scope similar to a credit-card application system) that supports:
- Secure user login
- User account opening
- ATM transactions (cash deposit and withdrawal)
- Intra-bank transfers
- Inter-bank transfers
- Querying transaction statistics within a specified time window
Assume web and mobile clients, multi-currency support, and integration with ATM and interbank networks. Aim for high availability, strong consistency for balances, and near real-time analytics.
Requirements
Describe:
- System architecture, core services, and data stores (e.g., user/account, ledger, ATM gateway, transfer orchestration).
- Data schema for users, accounts, balances, transactions, holds/ledger, and audit trails.
- API design, including idempotency for write operations.
- Transaction processing and concurrency control to prevent double spending.
- Consistency and recovery guarantees.
- External integrations for inter-bank transfers and ATM networks.
- Efficient time-window analytics (indexes, pre-aggregations, streaming, or OLAP).
- Scalability and availability strategies.
- Security controls (authentication, authorization, encryption).
- Failure handling and retries.
- Monitoring and on-call plan (key SLIs/SLOs, alerting rules, dashboards, runbooks).
Solution
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