Design Image Processing Infrastructure for mobile apps
Last updated: April 25, 2026
Quick Overview
Design a multi-tenant image processing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Reddit
System Design
Software Engineer
Software Engineer
Onsite
System Design
Medium
171
9
3,823 solved
Design a multi-tenant image processing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Reddit 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
- 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
Message queues and async processing
Security and authentication
Caching strategies (local, distributed, CDN)
Consistency models and replication
Partitioning and sharding strategies
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 monitoring and alerting would you set up on day one?
- 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:
- Support uploading, processing, and serving images for Reddit users on mobile apps.
- Multi-tenant architecture to handle images from various Reddit communiti...
Capacity Estimation
- Estimating Scale:
- Assume Reddit has around 50 million monthly active users.
- If 10% upload images daily, that’s 5 million uploads per day.
- Image processing requests can be es...
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