Design a geography-aware virtual card service

Q: Design a geography-aware virtual card service

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

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Scenario

You are asked to design a virtual card number product for a financial app.

Users can generate virtual card numbers to pay online/in-store. The product must support geography-aware behavior, such as:

Issuing card numbers that are valid only in certain countries/regions, or have region-specific limits
Handling multi-currency and cross-border usage
Supporting travel use cases (temporary region allow-lists)
Reducing fraud (e.g., card-not-present, unusual location)

Requirements

Functional

Create/activate/suspend/delete a virtual card
Configure controls: region allow/deny list, spend limits, merchant category restrictions, time windows
Authorize transactions and decide approve/decline in real time
Show transaction history per virtual card

Non-functional

Low-latency authorization (e.g., <150 ms p95 for decisioning layer)
High availability
Strong security (tokenization, access control)
Auditability and customer support traceability

Deliverables

Provide:

Components and data model
How authorization works end-to-end (including geo checks)
Fraud/risk integration
Key edge cases (travel, VPN, mismatched location signals, offline/partial data)