Design a Moderated Messaging Service
Company: Illumio
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
Design a one-to-one messaging system with the following requirements:
1. A user can send a message to another user.
2. Users can view their chat history.
3. Every outgoing message must be checked by an external AI moderation service for inappropriate text.
Discuss the end-to-end architecture, data model, APIs, and storage choices. Then address these follow-up questions:
- If a large burst of messages arrives, how would you prevent the system from crashing or running out of memory?
- The external AI service can be slow. How would you keep the user experience responsive while still preventing unsafe content from reaching recipients?
- How would you handle retries, failures, and duplicate processing?
Quick Answer: This question evaluates system design competency, covering scalable distributed architecture, data modeling, API design, integration with external moderation services, and operational concerns such as backpressure, retries, and duplicate processing.