Design a large-scale Chat Platform
Last updated: January 7, 2026
Quick Overview
Design a fault-tolerant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Adobe
January 7, 20266
5
4,597 solved
Design a fault-tolerant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Adobe 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 migrate from a monolithic to a microservices architecture?
- 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:
- Real-time messaging: Users can send and receive messages in real-time.
- Group chat: Support for group conversations with up to 100 participants.
- Message histo...
Capacity Estimation
Assuming an average of 100 messages per user per day, with 10 million concurrent users:
- Total Messages:
- Daily: 10,000,000 users * 100 messages/user = 1,000,000,000 messages/day
- Per secon...
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