Design a Order Processing Service
Last updated: July 20, 2025
Quick Overview
Design a event-driven order processing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Postmates
July 20, 2025274
8
3,423 solved
Design a event-driven order processing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Postmates typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
What the Interviewer Expects
- Clearly define functional and non-functional requirements
- Propose a reasonable high-level architecture with core components
- Choose appropriate data storage solutions with basic justification
- Discuss basic scaling strategies (horizontal scaling, caching)
- Identify potential bottlenecks and suggest simple solutions
Key Topics to Cover
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle schema migrations with zero downtime?
- How would you handle a 10x increase in traffic overnight?
- How do you ensure data consistency across multiple services?
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Requirements
Functional Requirements:
- Order Creation: Users can place orders for delivery with specified items and delivery address.
- Order Tracking: Users can track the status of their orders in ...
Capacity Estimation
Back-of-Envelope Calculations:
Assuming Postmates handles 1 million orders per day:
- Peak Hour Estimation: If we consider peak hours to handle 20% of the daily traffic, that would be approxim...
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