API Proxy Server

Overview

A production-ready API proxy server built with Node.js and Express that acts as an intermediary layer between client applications and external APIs. The server enhances security by hiding sensitive API keys, implements intelligent rate limiting to prevent abuse, and uses caching mechanisms to optimize performance and reduce external API calls.

Key Features

• API Key Protection: Securely stores and manages API keys on the server side, never exposing them to clients
• Rate Limiting: Configurable rate limits to prevent API abuse and control request frequency
• Intelligent Caching: Redis-based caching system to reduce redundant API calls and improve response times
• CORS Support: Flexible CORS configuration to control cross-origin requests
• Request Logging: Comprehensive logging with Morgan for monitoring and debugging
• Error Handling: Robust error handling with detailed error messages and status codes
• Security Headers: Helmet integration for enhanced security headers
• Environment Configuration: Secure environment variable management with dotenv
• Flexible Routing: Easy-to-configure routes for different API endpoints

Why I Built This

I created this proxy server to address common challenges in client-side API integration:

• Security: Prevent API key exposure in client-side code
• Cost Optimization: Reduce API costs through effective caching
• Performance: Improve response times with cached data
• Control: Implement granular access control and rate limiting
• Monitoring: Track API usage and identify potential issues
• Scalability: Build a reusable solution for multiple projects

Tech Stack

• Runtime: Node.js
• Framework: Express.js
• Caching: Redis / Node-Cache
• HTTP Client: Axios
• Security: Helmet, CORS
• Rate Limiting: Express-Rate-Limit
• Logging: Morgan
• Environment: Dotenv
• Development: Nodemon

Technical Highlights

Architecture

• Implemented a middleware-based architecture for modular request handling
• Designed a flexible routing system to support multiple API endpoints
• Used Redis for distributed caching in production environments

Security Features

• Hidden API keys stored securely in environment variables
• CORS configuration to control allowed origins
• Helmet middleware for security headers (XSS protection, content security policy)
• Input validation and sanitization

Performance Optimization

• Implemented intelligent caching with configurable TTL (Time To Live)
• Cache key generation based on request parameters
• Cache invalidation strategies for data freshness
• Response compression for faster data transfer

Rate Limiting

• Configurable rate limits per endpoint
• IP-based request tracking
• Custom rate limit responses
• Whitelist support for trusted clients

API Endpoints

// Example endpoint structure
GET  /api/proxy/*          - Proxy any GET request
POST /api/proxy/*          - Proxy any POST request
GET  /api/cache/stats      - Get cache statistics
GET  /api/health           - Health check endpoint

Configuration

// Environment Variables
PORT                       - Server port (default: 5000)
API_KEY                    - Your external API key
CACHE_TTL                  - Cache duration in seconds
RATE_LIMIT_WINDOW         - Rate limit window in ms
RATE_LIMIT_MAX_REQUESTS   - Max requests per window
REDIS_URL                 - Redis connection string

Challenges & Solutions

Implementing Secure API Key Management

Implemented environment variable system using dotenv to protect API keys from exposure. Keys are never committed to version control, with validation checks on server startup.

Rate Limiting Strategy Design

Built tiered rate limiting using express-rate-limit with IP-based tracking and Redis persistence. Added custom headers to inform clients of rate limit status.

Cache Invalidation Logic

Created multi-layered caching with configurable TTL values and cache keys based on request parameters. Implemented manual invalidation endpoints for critical updates.

Error Handling & Logging

Developed centralized error handling middleware with proper status codes. Integrated Morgan for request logging while sanitizing sensitive data.

CORS Configuration

Configured dynamic CORS with environment-based allowed origins, supporting wildcard subdomains and proper pre-flight request handling.

Performance Optimization

Implemented connection pooling with Axios, response compression with gzip, and O(1) Redis cache lookups for minimal latency.

Request/Response Transformation

Built middleware for request/response transformation that adds proxy metadata while preserving original data structure and filtering internal headers.

Use Cases

• Third-Party API Integration: Safely integrate external APIs without exposing keys
• Microservices Architecture: Act as an API gateway for microservices
• Cost Reduction: Minimize API costs through intelligent caching
• Mobile Apps: Provide a secure backend for mobile applications
• SaaS Products: Build multi-tenant applications with rate limiting

Problem Solved

Frontend applications often expose API keys in client-side code, creating security vulnerabilities. Additionally, direct API calls from clients lead to redundant requests, higher costs, and no control over usage. This proxy server solves these issues by acting as a secure intermediary that hides credentials, caches responses, and enforces rate limits.

What Makes It Unique

Most developers either expose API keys or build overly complex backend solutions. This proxy server provides a lightweight, reusable middleware layer that can be deployed once and used across multiple frontend projects. The combination of intelligent caching with Redis and configurable rate limiting makes it a complete API gateway solution in minimal code.

Impact

• Skill Development: Deepened my understanding of Express.js middleware architecture, security patterns, and API gateway design
• Reusable Asset: Created a template I can reuse in future projects requiring third-party API integration
• Security Awareness: Learned best practices for handling sensitive credentials and preventing common API security vulnerabilities

Future Enhancements

• Add authentication and authorization layer (JWT/OAuth)
• Implement request/response transformation
• Add API versioning support