Design a Chat for Netflix
Last updated: December 16, 2025
Quick Overview
Design a high-throughput chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Netflix
December 16, 2025414
11
2,848 solved
Design a high-throughput chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Netflix 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
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
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 do you ensure data consistency across multiple services?
- What monitoring and alerting would you set up on day one?
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Requirements
Functional Requirements:
- Real-time Messaging: Users must be able to send and receive messages instantly during viewing sessions.
- Group Chats: Support for group conversations where us...
Capacity Estimation
Assuming Netflix has approximately 200 million subscribers:
- Concurrent Users: Let's estimate that 10% (20 million) are active during peak times.
- Message Frequency: Assuming an average us...
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