Design a scalable banking system

Q: Design a scalable banking system

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

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Question

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).

Design a scalable banking system

System Design: Online Banking Platform

Context

Requirements

Solution (Locked)

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