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Microsoft·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Jun 2026

Summary

System design round at Microsoft for a software engineer role. The whole thing was one big question about building an image upload and download service, and they wanted you to cover basically everything: APIs, storage, CDN, security, the works. Dense but fair.

Questions Asked (1)

Q1

Design an image upload and download service for web and mobile clients. Walk through the full architecture including APIs, storage, processing pipeline, delivery, security, reliability, scalability, and observability.

System DesignTechnical Trade-offsAPI & Integrations
Author's notes

This question is basically nine questions stapled together and handed to you with a smile.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements (image types, sizes, scale, latency, security) and then present a high-level architecture covering upload, storage, processing, and delivery. Dive into each component with trade-offs, emphasizing scalability, reliability, and security, while aligning with Microsoft's cloud services like Azure Blob Storage and CDN.

Pro tip: Demonstrate awareness of cost and performance trade-offs by discussing tiered storage (hot vs. cold) and the use of serverless functions for on-demand image processing, which is a common pattern in Azure.

1. Clarify Requirements and Scope

Ask questions to understand expected scale (e.g., uploads per second, image size), latency requirements, client types, and security/compliance needs. This ensures the design meets the actual needs.

2. Design Upload and Storage

Outline the upload flow: clients request a pre-signed URL from an API, then upload directly to blob storage (e.g., Azure Blob Storage). Discuss storage tiers, redundancy, and metadata management.

3. Design Processing Pipeline

Describe asynchronous processing for image validation, resizing, format conversion, and thumbnail generation using a queue and serverless functions (e.g., Azure Functions). Mention idempotency and error handling.

4. Design Delivery and Caching

Explain how processed images are served via a CDN (e.g., Azure CDN) with appropriate caching headers. Discuss dynamic resizing on-the-fly or pre-generated variants, and secure access via signed URLs or tokens.

5. Address Cross-Cutting Concerns

Cover security (authentication, authorization, encryption), reliability (retries, dead-letter queues), scalability (horizontal scaling, partitioning), and observability (logging, metrics, tracing) using Azure Monitor and Application Insights.

Key Points to Mention

  • Use of pre-signed URLs for secure direct uploads to blob storage, reducing API server load.
  • Asynchronous processing with queues and serverless functions for scalability and cost-efficiency.
  • CDN integration for low-latency global delivery and caching strategies.
  • Security measures: authentication (OAuth), authorization, encryption at rest and in transit, and signed URLs for downloads.
  • Reliability patterns: retries with exponential backoff, dead-letter queues, and idempotent processing.
  • Observability: logging, metrics, and distributed tracing to monitor performance and troubleshoot issues.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.