This is a detailed system design document for Use Case 1: Dynamic User-Generated Content (UGC) Storage using an Object Storage solution.

1. Introduction

This document outlines the architecture, components, and flow for a robust, scalable, and cost-effective system to handle Dynamic User-Generated Content (UGC), such as profile pictures, blog post images, and short video clips. The core of this solution leverages Object Storage for its inherent scalability, durability, and cost-efficiency.

2. Goals and Requirements

Category	Requirement	Solution Component
Scalability	Must handle millions to billions of objects (files) with rapid growth.	Object Storage (e.g., AWS S3, Google Cloud Storage, Azure Blob Storage).
Durability	Data must be highly protected against loss.	Object Storage’s built-in multi-zone replication ($99.999999999\%$ durability).
Availability	Content must be accessible quickly and reliably.	Object Storage combined with a Content Delivery Network (CDN).
Cost	Storage costs must be optimized for varying access patterns.	Object Storage Tiering/Lifecycle Policies (e.g., moving old UGC to “Infrequent Access” tiers).
Security	Uploads must be secured, and only intended users/applications should access the content.	Pre-signed URLs and Bucket Policies/IAM Roles.
Performance	Fast retrieval of content for end-users.	CDN integration for edge-caching.

3. System Architecture Diagram

4. Component Deep Dive

4.1. Client Layer (User Interface)

Components: Web browser, Mobile application.

Function: Initiates the file upload process and later retrieves the content for display.

4.2. Application Backend (API/Service Layer)

Technology: Web framework (e.g., Node.js/Express, Python/Django/Flask, Java/Spring).

Function:
- Authentication & Authorization: Verifies the user’s identity and permissions for uploading/accessing content.
- Metadata Management: Stores the file’s unique identifier (URL/Key), user ID, upload date, and other relevant metadata in the Database.
- Upload Initiation: Requests a secure Pre-Signed URL from the Object Storage service for direct client-to-storage upload, bypassing the application server.

4.3. Database (Relational or NoSQL)

Technology: PostgreSQL, MySQL, MongoDB, DynamoDB.

Function: Stores the metadata associated with the UGC, not the file content itself.
- Schema Example: user_id, file_key (the object storage key/path), mime_type, upload_date, status (e.g., ‘pending’, ‘processed’, ‘live’).

4.4. Object Storage Pool (Core Component)

Technology: Amazon S3, Azure Blob Storage, Google Cloud Storage.

Function: Stores the raw UGC files (pictures, videos, documents).
- Bucket Structure: A logical container (Bucket/Container) holds all UGC. Keys are typically structured like paths: users/{user_id}/avatars/{timestamp}.jpg or posts/{post_id}/{file_hash}.mp4.
- Lifecycle Policies: Automatically transitions older or less-accessed objects to cheaper storage tiers (e.g., Standard $\rightarrow$ Infrequent Access $\rightarrow$ Archive), optimizing cost.

4.5. Content Delivery Network (CDN)

Technology: Amazon CloudFront, Cloudflare, Akamai, Google CDN.

Function: Caches frequently accessed UGC files at edge locations globally.
- Benefit: Reduces latency for users worldwide and offloads retrieval traffic from the Object Storage pool.
- Configuration: Configured to use the Object Storage Bucket as its origin.

4.6. Asynchronous Processing Queue (Optional but Recommended)

Technology: Amazon SQS, RabbitMQ, Kafka.

Function: Handles heavy, non-critical post-upload tasks (e.g., image resizing, video transcoding, malicious content scanning).

5. Simplified Workflow

5.1. UGC Upload Flow (Client $\rightarrow$ Storage)

Client Request: The user clicks “Upload,” and the Client sends a request to the Application Backend to begin the upload.

Authentication/Authorization: The Application Backend verifies the user’s identity and permission.

Pre-Signed URL Generation: The Application Backend generates a Pre-Signed URL from the Object Storage service. This URL grants temporary, secure upload access to a specific object key (path) without exposing cloud credentials.¹

Direct Upload: The Client uses the Pre-Signed URL to upload the file directly to the Object Storage Pool.² This minimizes server load and bandwidth costs on the Application Backend.

Metadata Storage: After a successful upload confirmation (from the storage service or a client callback), the Application Backend stores the file’s unique key (URL/Path) and any necessary metadata in the Database.

Processing (Async): An event (e.g., an S3 Notification) or a message is placed on the Processing Queue to handle necessary tasks (e.g., generating a 100×100 thumbnail).

5.2. UGC Retrieval Flow (Display)

View Request: A user requests a page that contains UGC (e.g., a profile page).

URL Lookup: The Application Backend queries the Database using the user ID (or post ID) to retrieve the Object Storage URL/Key.

Content Display: The Application Backend renders the page with the full Object Storage URL (often the CDN-aliased URL) embedded in the HTML (<img src="..."> or <video src="...">).

Edge Cache Check: The user’s browser attempts to fetch the file from the CDN.

Origin Fetch (if miss): If the file is not in the CDN cache (a “miss”), the CDN fetches it from the Object Storage Pool and then serves it to the user’s browser, caching it for future requests.

6. Security Considerations

Concern	Mitigation Strategy
Unauthorized Uploads	Use Pre-Signed URLs (time-limited, specific object key/action). Block direct API key access.
Public Exposure	Set a Bucket Policy to allow only the CDN (via an Origin Access Control/Identity – OAC/OAI) or anonymous read access to the bucket.
Malicious Content	Integrate a virus scanner into the Asynchronous Processing Pipeline before making content publicly viewable.
Data in Transit	Enforce HTTPS/TLS for all uploads (Pre-Signed URLs) and retrievals (CDN).