Architect a real-time Email Engine
Last updated: October 5, 2025
Quick Overview
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
TikTok
October 5, 202548
4
925 solved
Design a real-time email system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during Technical Screen at TikTok. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. TikTok values engineers who can think about scalability from day one.
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 migrate from a monolithic to a microservices architecture?
- How would you handle a region-wide outage?
- What monitoring and alerting would you set up on day one?
- How would you optimize costs as the system scales?
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Requirements
Functional Requirements
- Email Sending: The system should send emails in real-time to users based on actions taken (e.g., notifications for likes, comments, and messages).
- **Email Trackin...
Capacity Estimation
To estimate the capacity:
- User Base: Assume 1 billion users on TikTok.
- Daily Active Users: Let's say 20% are daily active, i.e., 200 million users.
- Emails per User: Assume an average...
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