Reverse Proxy

A reverse proxy sits between clients and servers, forwarding requests to backend servers.

Forward vs Reverse Proxy

Forward Proxy (client-side):
Client → Proxy → Internet
(Proxy hides client identity)

Reverse Proxy (server-side):
Client → Proxy → Server
(Proxy hides server identity)

How Reverse Proxy Works

                    ┌─────────────────┐
                    │  Reverse Proxy  │
                    │    (Nginx)      │
Client ────→ ─────→│                 │
                    │  ┌───────────┐  │
                    │  │ Request   │  │
                    │  │ Router    │  │
                    │  └─────┬─────┘  │
                    └────────┼─────────┘
               ┌─────────────┼─────────────┐
               │             │             │
        ┌──────▼──┐   ┌──────▼──┐   ┌──────▼──┐
        │Server 1 │   │Server 2 │   │Server 3 │
        └─────────┘   └─────────┘   └─────────┘

Reverse Proxy Functions

Function	Description
Load Balancing	Distribute requests across servers
SSL Termination	Handle HTTPS encryption/decryption
Caching	Cache static content
Compression	Compress responses
Rate Limiting	Limit request rates
Security	Hide backend servers
Logging	Centralized request logging

Client Perspective

Client sees:
- Single endpoint (proxy address)
- HTTPS (handled by proxy)
- Fast responses (cached)

Client doesn't see:
- Backend server architecture
- Number of servers
- Server software
- Internal network

Nginx is the most popular reverse proxy and web server.

Nginx Configuration

# Basic reverse proxy
upstream backend {
    server 127.0.0.1:3000;
    server 127.0.0.1:3001;
    server 127.0.0.1:3002;
}

server {
    listen 80;
    server_name example.com;

    location / {
        proxy_pass http://backend;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

Nginx Features

1. Load Balancing
   upstream backend {
       least_conn;  # Algorithm
       server 10.0.0.1:3000;
       server 10.0.0.2:3000;
   }

2. SSL Termination
   server {
       listen 443 ssl;
       ssl_certificate /path/to/cert.pem;
       ssl_certificate_key /path/to/key.pem;
       # Backend gets HTTP
   }

3. Caching
   proxy_cache_path /tmp/cache levels=1:2;
   location /static/ {
       proxy_cache my_cache;
       proxy_cache_valid 200 1h;
   }

4. Rate Limiting
   limit_req_zone $binary_remote_addr zone=api:10m rate=10r/s;
   location /api/ {
       limit_req zone=api burst=20;
   }

Nginx vs Apache

Aspect	Nginx	Apache
Architecture	Event-driven	Process/thread-based
Performance	Higher concurrency	Lower concurrency
Memory	Lower usage	Higher usage
Config	Declarative	.htaccess
Use Case	Reverse proxy, static	Dynamic content

Common Nginx Patterns

1. Static file serving
   location /static/ {
       root /var/www;
       expires 30d;
   }

2. API proxy
   location /api/ {
       proxy_pass http://api_backend;
   }

3. WebSocket proxy
   location /ws/ {
       proxy_pass http://ws_backend;
       proxy_http_version 1.1;
       proxy_set_header Upgrade $http_upgrade;
   }

Reverse proxies provide significant benefits for production systems.

Security Benefits

1. Hide Backend Architecture
   Client → Proxy → Server1, Server2, Server3
   Client can't see server IPs or count

2. SSL Termination
   Client ←──HTTPS──→ Proxy ←──HTTP──→ Server
   Servers don't handle SSL overhead

3. DDoS Protection
   - Rate limiting
   - IP blocking
   - Request validation

4. WAF (Web Application Firewall)
   - SQL injection prevention
   - XSS prevention
   - Bot detection

Performance Benefits

1. Caching
   - Static files cached at proxy
   - Reduces backend load

2. Compression
   - gzip/brotli compression
   - Reduces bandwidth

3. Connection Pooling
   - Reuse backend connections
   - Reduce overhead

4. SSL Offloading
   - Dedicated SSL processing
   - Better performance

Operational Benefits

1. Centralized Logging
   All requests logged at proxy level

2. Easy Backend Changes
   Add/remove servers without client impact

3. Zero-Downtime Deployment
   - Rolling updates
   - Blue-green deployment

4. Health Checks
   Monitor backend health
   Remove unhealthy servers

Use Cases

Use Case	How Proxy Helps
Web application	Load balancing, SSL, caching
Microservices	API gateway, routing
API management	Rate limiting, authentication
Static site	CDN, caching
Legacy modernization	New frontend, old backend

Architecture with Reverse Proxy

                    ┌─────────────┐
                    │   Nginx     │
                    │   (Proxy)   │
Client ────HTTPS───→│             │
                    │  SSL Term   │
                    │  Cache      │
                    │  Rate Limit │
                    └──────┬──────┘
                           │
              ┌────────────┼────────────┐
              │            │            │
       ┌──────▼──┐  ┌──────▼──┐  ┌──────▼──┐
       │Web App 1│  │Web App 2│  │API Server│
       └─────────┘  └─────────┘  └──────────┘