Design a Messaging Service
Last updated: January 21, 2026
Quick Overview
Design a real-time messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Shopify
January 21, 202610
13
2,025 solved
Design a real-time messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Shopify 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 a region-wide outage?
- How would you handle schema migrations with zero downtime?
- What would the deployment pipeline look like for this system?
- What happens if one of your database nodes goes down?
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Requirements
Functional Requirements
- Real-time Messaging: Users should be able to send and receive messages instantly.
- Group Messaging: Support for group chats where multiple users can participat...
Capacity Estimation
Assuming Shopify has 1 million active users, with an average of 10 messages sent per user per day:
- Total Messages per Day: 1,000,000 users * 10 messages = 10,000,000 messages/day.
- **Peak Loa...
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