Nginx reverse proxy and load balancing

                  # Main nginx.conf

worker_processes auto;
worker_rlimit_nofile 65535;

events {
    worker_connections 4096;
    multi_accept on;
    use epoll;
}

http {
    # Basic settings
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    server_tokens off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    # Logging
    log_format main '$remote_addr - $remote_user [$time_local] '
                    '"$request" $status $body_bytes_sent '
                    '"$http_referer" "$http_user_agent" '
                    '$request_time $upstream_response_time';

    access_log /var/log/nginx/access.log main;
    error_log /var/log/nginx/error.log warn;

    # Gzip compression
    gzip on;
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_min_length 1024;
    gzip_types
        text/plain
        text/css
        text/xml
        text/javascript
        application/json
        application/javascript
        application/xml
        image/svg+xml;

    # Rate limiting
    limit_req_zone $binary_remote_addr zone=api:10m rate=10r/s;
    limit_req_zone $binary_remote_addr zone=login:10m rate=1r/s;

    # Upstream backends
    upstream app_servers {
        least_conn;
        server app1:3000 weight=3;
        server app2:3000 weight=2;
        server app3:3000 weight=1;
        server app4:3000 backup;

        keepalive 32;
    }

    # 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;

    # HTTP → HTTPS redirect
    server {
        listen 80;
        server_name app.example.com;
        return 301 https://$server_name$request_uri;
    }

    # Main HTTPS server
    server {
        listen 443 ssl http2;
        server_name app.example.com;

        # SSL
        ssl_certificate /etc/nginx/certs/fullchain.pem;
        ssl_certificate_key /etc/nginx/certs/privkey.pem;
        ssl_protocols TLSv1.2 TLSv1.3;
        ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
        ssl_prefer_server_ciphers off;
        ssl_session_cache shared:SSL:10m;
        ssl_session_timeout 1d;

        # Security headers
        add_header X-Frame-Options "SAMEORIGIN" always;
        add_header X-Content-Type-Options "nosniff" always;
        add_header X-XSS-Protection "1; mode=block" always;
        add_header Referrer-Policy "strict-origin-when-cross-origin" always;
        add_header Content-Security-Policy "default-src 'self'" always;
        add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always;

        # Static files
        location /static/ {
            alias /var/www/static/;
            expires 1y;
            add_header Cache-Control "public, immutable";
            access_log off;
        }

        # API with rate limiting
        location /api/ {
            limit_req zone=api burst=20 nodelay;

            proxy_pass http://app_servers;
            proxy_http_version 1.1;
            proxy_set_header Connection "";
            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_connect_timeout 5s;
            proxy_send_timeout 30s;
            proxy_read_timeout 30s;

            # Caching
            proxy_cache app_cache;
            proxy_cache_valid 200 10m;
            proxy_cache_valid 404 1m;
            proxy_cache_use_stale error timeout updating;
            add_header X-Cache-Status $upstream_cache_status;
        }

        # Login with strict rate limiting
        location /auth/login {
            limit_req zone=login burst=3 nodelay;

            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;
        }

        # WebSocket support
        location /ws/ {
            proxy_pass http://app_servers;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";
            proxy_set_header Host $host;
            proxy_read_timeout 86400;
        }

        # Default proxy
        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;
        }

        # Health check endpoint
        location /nginx-health {
            access_log off;
            return 200 "healthy";
            add_header Content-Type text/plain;
        }
    }
}