Design a secure trading app on AWS

Q: Design a secure trading app on AWS

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

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Question

Scenario

Design a secure, Robinhood-like mobile/web application on AWS, with a deep dive into:

User profile management (account creation, authentication, PII storage, profile updates)
Stock query (searching symbols and retrieving near-real-time quotes)

Assume this is a regulated financial product (PII, auditability, strong security). You may treat order placement/execution as out of scope unless needed for completeness.

Functional requirements

User profile management

Sign up / sign in / sign out
MFA support
Store and manage user profile data (name, email/phone, address, KYC status, preferences)
Allow profile updates (with appropriate authorization and audit trail)
Account recovery (password reset)

Stock query

Search stocks by ticker/company name (prefix search)
Fetch a quote for a symbol (price, bid/ask, timestamp)
Handle high read QPS with low latency

Non-functional requirements

Strong security: encryption, least privilege, secrets management, WAF/rate limiting
Compliance/audit: immutable logs of profile changes and access
High availability and scalability
Reasonable freshness for quotes (e.g., seconds), with graceful degradation

Deliverables

High-level architecture on AWS
Key data models/stores
API surface (example endpoints)
Security model and threat mitigations
Scalability and reliability approach (caching, multi-AZ/region, DR)