การตั้งค่า Nginx Reverse Proxy: Load Balancing, SSL และ Caching

A reverse proxy sits between your clients and backend servers, forwarding requests and returning responses. Nginx is the most popular choice for this role in 2026 — it handles SSL termination, load balancing, caching, and WebSocket proxying with minimal configuration. This guide covers every production-ready pattern you need.

# proxy_pass trailing slash behavior
# Rule: proxy_pass with a URI replaces the matching location prefix.
#       proxy_pass without a URI passes the full original request URI.

server {
    listen 80;
    server_name example.com;

    # Keep the /api/ prefix on the upstream request
    # Request:  /api/users?id=1
    # Upstream: http://api_backend/api/users?id=1
    location /api/ {
        proxy_pass http://api_backend;
    }

    # Strip the /app/ prefix before forwarding
    # Request:  /app/dashboard
    # Upstream: http://app_backend/dashboard
    location /app/ {
        proxy_pass http://app_backend/;
    }

    # Replace /docs/ with /manual/
    # Request:  /docs/install.html
    # Upstream: http://docs_backend/manual/install.html
    location /docs/ {
        proxy_pass http://docs_backend/manual/;
    }

    # In regex or named locations, do not add a URI part to proxy_pass.
    # Use rewrite or pass the full request URI explicitly instead.
    location ~ ^/files/(.*)$ {
        proxy_pass http://file_backend;
    }
}

Basic Reverse Proxy Setup

The simplest reverse proxy forwards all requests to a single backend server. The key headers ensure your backend sees the real client IP and protocol.

# Basic reverse proxy configuration
server {
    listen 80;
    server_name example.com www.example.com;

    location / {
        proxy_pass http://localhost:3000;

        # Pass original request headers to the 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;
        proxy_set_header X-Forwarded-Proto $scheme;

        # Timeouts (seconds)
        proxy_connect_timeout 60s;
        proxy_send_timeout    60s;
        proxy_read_timeout    60s;

        # Buffer settings
        proxy_buffering    on;
        proxy_buffer_size  16k;
        proxy_buffers      4 16k;
    }
}

SSL/TLS Termination

SSL termination at Nginx means your backend servers only handle HTTP internally, simplifying their configuration. Nginx handles the encryption overhead.

# Full SSL/TLS reverse proxy with HTTP redirect
server {
    listen 80;
    server_name example.com www.example.com;
    # Permanent redirect all HTTP traffic to HTTPS
    return 301 https://$server_name$request_uri;
}

server {
    listen 443 ssl http2;
    server_name example.com www.example.com;

    # SSL certificate (Let's Encrypt)
    ssl_certificate     /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    # Modern SSL settings (2026 recommended)
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305;
    ssl_prefer_server_ciphers off;

    # SSL session cache
    ssl_session_timeout 1d;
    ssl_session_cache shared:SSL:10m;
    ssl_session_tickets off;

    # HSTS: tell browsers to always use HTTPS (6 months)
    add_header Strict-Transport-Security "max-age=15768000" always;

    # OCSP stapling
    ssl_stapling on;
    ssl_stapling_verify on;
    resolver 8.8.8.8 8.8.4.4 valid=300s;

    location / {
        proxy_pass http://localhost:3000;
        proxy_set_header Host              $host;
        proxy_set_header X-Real-IP         $remote_addr;
        proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Upstream Blocks and Load Balancing

The upstream block defines a pool of backend servers. Nginx supports round-robin, least-connections, and IP-hash load balancing algorithms.

# Load balancing across multiple backends
upstream app_servers {
    # Default: round-robin
    server 10.0.0.1:3000;
    server 10.0.0.2:3000;
    server 10.0.0.3:3000;

    # Least connections algorithm
    # least_conn;

    # IP hash (sticky sessions)
    # ip_hash;

    # Weighted distribution
    # server 10.0.0.1:3000 weight=3;
    # server 10.0.0.2:3000 weight=1;

    # Health checks (Nginx Plus only; use passive for open-source)
    server 10.0.0.3:3000 max_fails=3 fail_timeout=30s;

    # Keepalive connections to backends
    keepalive 32;
}

server {
    listen 443 ssl http2;
    server_name example.com;

    # ... SSL config omitted for brevity ...

    location / {
        proxy_pass http://app_servers;

        proxy_set_header Host              $host;
        proxy_set_header X-Real-IP         $remote_addr;
        proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header Connection        "";
        proxy_http_version 1.1;

        proxy_connect_timeout 5s;
        proxy_read_timeout    60s;
    }
}

WebSocket Proxying

WebSocket connections require special handling because they upgrade from HTTP to a persistent TCP connection. The Upgrade and Connection headers must be forwarded.

# WebSocket proxy configuration
server {
    listen 443 ssl http2;
    server_name ws.example.com;

    # ... SSL config ...

    location /ws/ {
        proxy_pass http://localhost:8080;

        # WebSocket upgrade headers
        proxy_http_version 1.1;
        proxy_set_header Upgrade    $http_upgrade;
        proxy_set_header Connection "upgrade";

        proxy_set_header Host            $host;
        proxy_set_header X-Real-IP       $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

        # Long timeout for persistent connections
        proxy_read_timeout 3600s;
        proxy_send_timeout 3600s;
    }

    # Regular HTTP traffic on the same server
    location / {
        proxy_pass http://localhost:3000;
        proxy_set_header Host              $host;
        proxy_set_header X-Forwarded-For   $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Proxy Caching

Nginx can cache backend responses to reduce load and improve latency for cacheable content.

# Caching with proxy_cache
proxy_cache_path /var/cache/nginx
    levels=1:2
    keys_zone=app_cache:10m
    max_size=1g
    inactive=60m
    use_temp_path=off;

server {
    listen 443 ssl http2;
    server_name example.com;

    # ... SSL config ...

    location / {
        proxy_pass http://localhost:3000;
        proxy_set_header Host $host;

        # Enable cache
        proxy_cache         app_cache;
        proxy_cache_key     "$scheme$request_method$host$request_uri";
        proxy_cache_valid   200 302 10m;
        proxy_cache_valid   404     1m;

        # Return stale content while refreshing
        proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;

        # Add cache status header for debugging
        add_header X-Cache-Status $upstream_cache_status;

        # Don't cache if Cookie or Authorization header present
        proxy_cache_bypass $http_cookie $http_authorization;
        proxy_no_cache     $http_cookie $http_authorization;
    }

    # Bypass cache for API routes
    location /api/ {
        proxy_pass http://localhost:3000;
        proxy_cache_bypass 1;
        proxy_no_cache     1;
    }
}

Quick Reference: Key Directives

Production Best Practices

1. Always test configuration before reloading: nginx -t. Never reload without testing in production.
2. Use proxy_set_header X-Forwarded-Proto $scheme so your backend knows whether the original request was HTTP or HTTPS.
3. Set appropriate timeouts. The default proxy_read_timeout is 60s — increase for long-running requests (file uploads, reports).
4. Enable keepalive connections to backends using proxy_http_version 1.1 and keepalive in the upstream block for better performance.
5. Monitor /var/log/nginx/error.log and access.log. Set up log rotation with logrotate.

Frequently Asked Questions