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File Upload Service

Design scalable file uploads with presigned URLs and metadata.

1h 30m
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Topic Progress0%

Requirements & Scope

Upload Flow (Presigned URL)

  1. Client requests presigned URL from API
  2. API generates URL with expiration (15 min)
  3. Client uploads directly to storage (S3)
  4. Client notifies API of completion
  5. API processes file (thumbnails, indexing)

Scale

  • 1M files/day
  • Average 5MB, up to 5GB
  • 5TB/month storage growth

Key Points

  • Understanding File Upload Service is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Architecture & Presigned URLs

Multipart Upload for Large Files

  1. Initiate multipart upload -> UploadId
  2. For each chunk (5MB-100MB): Upload part with PartNumber + ETag
  3. Complete multipart upload with all ETags
  4. If failed, abort and retry from last successful part

Storage Architecture

  • Hot data (recent): S3 Standard
  • Warm data (30-90 days): S3 Infrequent Access
  • Cold data (90+ days): S3 Glacier
  • Metadata: PostgreSQL with full-text search

Key Points

  • Understanding File Upload Service is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Database Design

Tables

  • files(id, owner_id, original_name, storage_key, mime_type, size_bytes, status, tags)
  • multipart_uploads(id, file_id, upload_id, total_parts, completed_parts, status)
  • upload_parts(id, upload_id, part_number, etag, size_bytes, status)

Key Points

  • Understanding File Upload Service is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0/3solved
Implement File Upload Service

Design and implement a solution for File Upload Service in a backend system. Consider scalability, error handling, and production readiness.

Solution
// File Upload Service implementation
// Key aspects: validation, error handling, logging, testing

public class FileUploadService {
    // Production-ready implementation
}
File Upload Service Edge Cases

Identify and handle edge cases for File Upload Service. What happens under high load, with invalid input, or during failures?

Solution
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
File Upload Service Testing Strategy

Write a testing strategy for File Upload Service. Include unit tests, integration tests, and performance tests.

Solution
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. Why use presigned URLs for file upload?

Question 1 options

2. What is the minimum chunk size for S3 multipart upload?

Question 2 options

3. What is the primary purpose of File Upload Service?

Question 3 options

4. What is a common mistake when implementing File Upload Service?

Question 4 options

Flashcards

Question

Why presigned URLs?

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Answer

Offload upload bandwidth to storage provider

Question

Min multipart chunk size?

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Answer

5MB for S3

Question

What is File Upload Service?

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Answer

File Upload Service is a key concept in backend development.

Question

When to use File Upload Service?

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Answer

Use File Upload Service when building production systems that require reliability, scalability, and maintainability.

Question

File Upload Service best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1.Presigned URLs offload bandwidth
  • 2.Multipart handles large files with resume
  • 3.Track upload state in database
  • 4.Use storage tiers for cost optimization

Interview Tips

  • •Explain why presigned URLs are better
  • •Design the state machine for uploads

Cheat Sheet

File Upload Service

  • Presigned URLs: Client uploads directly to S3
  • Multipart: 5MB chunks, resume on failure
  • Metadata: PostgreSQL with search
  • Tiers: Standard -> IA -> Glacier