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Google·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
May 2026Bay Area

Summary

Google system design interview for what seemed like a mid-to-senior engineering or TPM role. Single question about designing a billing system, which sounds straightforward until you actually start pulling on the threads.

Questions Asked (1)

Q1

Design a billing system for a doctor's office that operates across two locations in the Bay Area.

System DesignData ModelingTechnical Trade-offs
Author's notes

I went straight to the data model and kind of forgot to ask clarifying questions first, which I regretted pretty quickly.

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AI HintsAI Generated

Suggested Approach

Start by clarifying functional and non-functional requirements, such as patient billing, insurance claims, and multi-location support. Then propose a high-level architecture with separate services for billing, payments, and claims, and dive into data modeling and trade-offs.

Pro tip: Emphasize data consistency and idempotency in payment processing, as these are critical in healthcare billing where errors can have legal and financial repercussions.

1. Clarify Requirements

Ask questions to understand the scope: patient volume, insurance integration, payment methods, reporting needs, and compliance (e.g., HIPAA).

2. High-Level Design

Outline main components: patient management, billing service, payment gateway, insurance claims processor, and reporting. Consider a microservices architecture for scalability.

3. Data Modeling

Design core entities: Patient, Appointment, Invoice, Payment, InsuranceClaim. Define relationships and consider multi-tenancy for two locations.

4. Deep Dive into Key Flows

Detail the billing process: generating invoices from appointments, submitting claims, processing payments, and handling denials. Discuss idempotency and consistency.

5. Address Trade-offs and Scalability

Discuss trade-offs like SQL vs NoSQL, synchronous vs asynchronous processing, and how to scale for growth. Mention monitoring and auditing.

Key Points to Mention

  • HIPAA compliance and data security
  • Idempotent payment processing to avoid double-charging
  • Integration with insurance clearinghouses (e.g., Availity)
  • Multi-location support with centralized reporting
  • Handling of different payment methods (credit card, cash, insurance)
  • Audit trails and logging for financial transactions

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.