Build a geo-distributed Messaging Pipeline
Last updated: October 28, 2025
Quick Overview
Design a geo-distributed messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Citadel
October 28, 202544
7
1,067 solved
Design a geo-distributed messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Citadel 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 would the deployment pipeline look like for this system?
- How would you handle a region-wide outage?
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Requirements
Functional Requirements
- Message Production: Users can produce messages that can be sent to one or multiple destinations.
- Message Consumption: Consumers can subscribe to specific topics...
Capacity Estimation
Assuming Citadel's messaging pipeline needs to handle 10 million messages per second, here's a rough estimate:
- Daily Messages: 10 million messages/second * 86400 seconds = 864 billion messages/d...
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