Design Chat Infrastructure for global users
Last updated: February 27, 2026
Quick Overview
Design a multi-tenant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Datadog
February 27, 2026157
7
119 solved
Design a multi-tenant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Datadog 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 implement rate limiting to protect the system?
- What happens if one of your database nodes goes down?
- How would you handle schema migrations with zero downtime?
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Requirements
Functional Requirements
- User Authentication: Support OAuth2 and API keys for secure user authentication.
- Real-time Messaging: Users should be able to send and receive messages in rea...
Capacity Estimation
Assuming Datadog has around 10 million users, with an average of 10 messages per user per day:
- Total Messages per Day: 10 million users * 10 messages = 100 million messages/day.
- **Peak Load Ca...
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