Design image upload end-to-end

Q: Design image upload end-to-end

This question evaluates a candidate's ability to architect scalable, reliable end-to-end image upload systems, covering object storage and CDN integration, authentication and authorization, upload strategies (including chunked/resumable flows), validation and virus scanning, metadata extraction and sanitization, asynchronous processing and image transformations, storage/versioning and deduplication, database idempotency, caching/invalidation, error handling, observability, cost optimization, and multi-region scaling. Commonly asked in System Design interviews to assess trade-off reasoning, operational awareness, and both high-level architectural thinking and practical application-level design considerations within the System Design domain, it tests conceptual understanding as well as practical implementation concerns.

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Question

System Design: End-to-End Image Upload Pipeline

Context

Design an end-to-end system that handles user picture uploads from web or mobile clients through the backend and storage/CDN layers. Assume an object store (e.g., S3/GCS), a CDN, an API service, a background processing tier, and a relational database. Images are typically user-generated (e.g., profile or listing pictures), with typical sizes up to 20 MB, and must be delivered globally.

Requirements

Describe, in detail, how the system handles:

Request flow from browser/app through backend and storage/CDN.
Authentication and authorization.
Upload strategies: direct-to-object-store vs. server-proxied.
Chunked uploads and resume support.
Client- and server-side validation (file type/size, checksums, virus scanning).
Metadata extraction (e.g., EXIF) and sanitization.
Asynchronous processing pipelines/queues.
Image processing (resize/thumbnailing, formats, orientation).
Storage strategy and versioning, including deduplication and lifecycle.
Database writes and idempotency.
CDN caching and invalidation strategies.
Error handling and retries across components.
Observability and alerting.
Performance and cost considerations.
Horizontal scaling and multi-region considerations.

Clearly explain trade-offs and provide guardrails for safe operation. Use small numeric examples where helpful.

Design image upload end-to-end

System Design: End-to-End Image Upload Pipeline

Context

Requirements

Solution

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Design image upload end-to-end

Overview

System Design: End-to-End Image Upload Pipeline

Context

Requirements

Solution

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