Design a event-driven Chat System
Last updated: March 28, 2026
Quick Overview
Design a event-driven chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Postmates
System Design
Software Engineer
Postmates
March 28, 2026Software Engineer
Onsite
System Design
Easy
160
13
1,721 solved
Design a event-driven chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Postmates asks this during the Onsite to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
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
Load balancing and horizontal scaling
Message queues and async processing
Caching strategies (local, distributed, CDN)
Monitoring, logging, and alerting
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
- What would the deployment pipeline look like for this system?
- How would you implement rate limiting to protect the system?
- How would you handle a region-wide outage?
- How would you optimize costs as the system scales?
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Requirements
Functional Requirements
- User Authentication: Users can sign up, log in, and manage their profiles securely.
- Real-time Messaging: Users can send and receive messages instantly within ...
Capacity Estimation
Capacity Estimation
- User Base: Assume Postmates has 10 million active users.
- Concurrent Users: Estimate 1 million concurrent users during peak times.
- Message Volume: Each user...
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