Architect a scalable Inventory Management Engine

Last updated: October 3, 2025

Quick Overview

Design a scalable inventory management system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.

Doordash
System Design
Software Engineer
Doordash
October 3, 2025
Software Engineer
Technical Screen
System Design
Hard

199

6

3,780 solved


Design a scalable inventory management system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.

ML system design at Doordash goes beyond model selection. This Technical Screen question evaluates your ability to design end-to-end ML pipelines, from data collection to model serving, while considering production constraints like latency and reliability.

What the Interviewer Expects
  • Design the full ML lifecycle from data collection to model monitoring
  • Address cold start, exploration/exploitation, and model freshness
  • Discuss multi-objective optimization and ranking systems
  • Plan for model debugging, fairness, and bias mitigation
  • Design the feature store and training pipeline for scale
  • Address model versioning, canary deployments, and rollback strategies
  • Discuss the data flywheel and long-term system evolution
Key Topics to Cover
Data collection and labeling strategy
Feature engineering and feature stores
Model serving and latency optimization
Monitoring and model degradation detection
How to Approach This
  1. Start by clarifying functional and non-functional requirements with the interviewer.
  2. Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
  3. Draw a high-level architecture first, then deep dive into 1-2 critical components.
  4. Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
  5. Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
  • What would you do if model performance degrades over time?
  • What is your model retraining strategy?
  • How would you handle a 10x increase in prediction requests?
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Sample Answer
Requirements

Functional Requirements

  1. Inventory Tracking: Track real-time inventory levels for products across multiple warehouses and restaurants.
  2. Stock Alerts: Notify relevant stakeholders when ...
Capacity Estimation

For capacity estimation, we will consider the following metrics:

  • Daily Active Users: Assume 1 million daily active users.
  • Requests per User: Each user generates approximately 5 requests pe...

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