Build a event-driven Messaging Pipeline
Last updated: July 10, 2025
Quick Overview
Design a event-driven messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PayPal
July 10, 20254
8
1,040 solved
Design a event-driven messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during System Design Round at PayPal. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. PayPal values engineers who can think about scalability from day one.
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:
- Message Queuing: The system should allow producers to send messages and consumers to receive them in an event-driven manner.
- At-Least-Once Delivery: En...
Capacity Estimation
To estimate the capacity needed for the messaging pipeline, assume:
- Number of Messages: 10 million messages per day.
- Average Message Size: 1 KB.
Calculating the total storage needed:
- Da...
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