S3 Proxy Cache Service Technical Documentation

Overview

The S3 Proxy Cache Service is a Go-based middleware that provides a caching layer in front of S3-compatible storage services. It implements a RESTful API using the standard net/http package to handle object storage operations while maintaining an in-memory cache to improve read performance and reduce backend load.

Goals

• Provide a caching layer for S3-compatible storage services
• Reduce latency for frequently accessed objects
• Minimize backend storage load
• Maintain consistency between cache and storage
• Handle concurrent requests efficiently
• Follow clean architecture principles

Architecture

System Architecture

graph TD
    Client[Client] -->|HTTP Request| Middleware[Middleware Layer]
    Middleware -->|Request Processing| Router[Router Layer]
    Router -->|Route to Handler| Handlers[Handler Layer]
    Handlers -->|Cache Check| Cache[In-Memory Cache]
    Cache -->|Cache Hit| Handlers
    Handlers -->|Cache Miss| Storage[Storage Layer]
    Storage -->|Response| Handlers
    Handlers -->|Update Cache| Cache

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Component Architecture

graph TD
    subgraph API_Layer[API Layer]
        Router[Router Package]
        Middleware[Middleware Package]
        Handlers[Handlers Package]
    end
    
    subgraph Cache_Layer[Cache Layer]
        CacheEntry[CacheEntry Structure]
        CacheManagement[Cache Management]
        CleanupRoutine[Cleanup Routine]
    end
    
    subgraph Storage_Layer[Storage Layer]
        MinioClient[Minio Client]
        S3Operations[S3 Operations]
    end
    
    Router --> Handlers
    Middleware --> Router
    Handlers --> Cache_Layer
    Cache_Layer --> Storage_Layer

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Project Structure

.
├── cmd/
│   └── server/
│       └── main.go
└── internal/
    ├── middleware/
    │   ├── logging.go
    │   └── middleware.go
    ├── handlers/
    │   ├── health.go
    │   └── object.go
    ├── router/
    │   └── router.go
    ├── cache/
    │   └── cache.go
    ├── config/
    │   └── config.go
    └── storage/
        └── storage.go

Modules

Router Module

• Framework: Standard net/http
• Components:
  • Router setup and configuration
  • Middleware chain management
  • Route registration

Middleware Module

• Logging middleware with request/response tracking
• Middleware chaining support
• Extensible middleware architecture

Handlers Module

• Object Handler:
  • GET /objects/:bucket/*key: Retrieve objects with caching
  • PUT /objects/:bucket/*key: Upload objects and invalidate cache
  • DELETE /objects/:bucket/*key: Remove objects and invalidate cache
  • HEAD /objects/:bucket/*key: Retrieve object metadata with caching
• Health Handler:
  • GET /health: Service health check

Cache Module

• Type: In-memory cache using sync.Map
• Configuration:
  • Default TTL: 5 minutes
  • Maximum cache size: 100MB
  • Cleanup interval: 1 minute
• Features:
  • Thread-safe operations
  • LRU-like eviction policy
  • Automatic cleanup of expired entries
  • Size-based eviction
  • Compression support for large objects

Storage Module

• Client: Minio SDK
• Features:
  • S3-compatible interface
  • Configurable endpoints
  • SSL support
  • Error handling for common scenarios

Data Models

CacheEntry Structure

type CacheEntry struct {
    Data           []byte
    CompressedData []byte
    ContentType    string
    Size          int64
    LastModified  time.Time
    ETag          string
    ExpiresAt     time.Time
    IsCompressed  bool
}

Infrastructure Setup

Environment Variables

• S3_ENDPOINT: S3-compatible storage endpoint (default: "localhost:9000")
• S3_ACCESS_KEY: Access key for authentication (default: "minioadmin")
• S3_SECRET_KEY: Secret key for authentication (default: "minioadmin")
• S3_USE_SSL: Enable/disable SSL (default: "false")

Dependencies

• minio-go: S3 client SDK
• log/slog: Structured logging

API Reference

GET /objects/:bucket/*key

• Description: Retrieves an object from cache or storage
• Parameters:
  • bucket: Storage bucket name
  • key: Object key path
• Response:
  • 200: Success with object data
  • 404: Object not found
  • 500: Internal server error
• Headers:
  • Content-Type: Object MIME type
  • Content-Length: Object size
  • Last-Modified: Object modification time
  • ETag: Object entity tag
  • Content-Encoding: gzip (when compressed)

PUT /objects/:bucket/*key

• Description: Uploads an object and invalidates cache
• Parameters:
  • bucket: Storage bucket name
  • key: Object key path
• Request:
  • Body: Object data
  • Content-Type: Object MIME type
  • Content-Encoding: gzip (optional)
• Response:
  • 200: Success
  • 400: Bad request
  • 500: Internal server error

DELETE /objects/:bucket/*key

• Description: Removes an object and invalidates cache
• Parameters:
  • bucket: Storage bucket name
  • key: Object key path
• Response:
  • 204: Success
  • 404: Not found
  • 500: Internal server error

HEAD /objects/:bucket/*key

• Description: Retrieves object metadata from cache or storage
• Parameters:
  • bucket: Storage bucket name
  • key: Object key path
• Response:
  • 200: Success with metadata headers
  • 404: Object not found
  • 500: Internal server error

Logging and Monitoring

Structured Logging

• Uses log/slog for structured JSON logging
• Log levels: INFO, ERROR
• Key metrics logged:
  • Request duration
  • Response size
  • Status code
  • Remote address
  • User agent

Metrics to Track

• Cache hit/miss ratio
• Cache size utilization
• Request latency
• Error rates
• Backend storage operations

Security Practices

Authentication

• Uses static credentials for S3 authentication
• Supports SSL for secure communication

Thread Safety

• Uses sync.Map for thread-safe cache operations
• Implements mutex locks for cache size management
• Handles concurrent requests safely

Best Practices

Clean Architecture

1. Separation of concerns with distinct packages
2. Dependency injection for better testability
3. Interface-based design
4. Middleware chain pattern

Cache Management

1. Size-based eviction
2. Automatic cleanup routine
3. Cache consistency
4. Compression support for large objects

Error Handling

1. Proper error propagation
2. Specific error status codes
3. Storage-specific error handling
4. Graceful degradation

Performance Optimization

1. In-memory caching
2. Efficient memory usage
3. Concurrent operations
4. Compression support

Recommendations for Improvement

1. Implementation Enhancements:

   • Add request validation middleware
   • Implement rate limiting
   • Add cache statistics endpoints
   • Implement request tracing

2. Security Enhancements:

   • Add authentication middleware
   • Implement bucket access controls
   • Add request signing
   • Enhance audit logging

3. Operational Enhancements:

   • Add metrics middleware
   • Implement distributed caching
   • Add cache warmup strategies
   • Include backup procedures

4. Performance Enhancements:

   • Optimize compression strategies
   • Implement partial object caching
   • Add batch operations
   • Include cache preloading

Maintenance Tasks

• Regular cache size monitoring
• Performance profiling
• Security updates
• Dependency management