nginx.conf

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

http {
    # Basic Settings
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    client_max_body_size 20M;

    # Gzip Compression
    gzip on;
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_types text/plain text/css text/xml text/javascript 
               application/json application/javascript application/xml+rss;

    # Logging
    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log warn;

    # Upstream Backend Servers
    upstream sms_backend {
        least_conn;  # Load balancing method: least connections
        
        # Health check parameters
        server app:8080 max_fails=3 fail_timeout=30s weight=1;
        
        # When using Docker Compose with replicas, 
        # Docker will automatically distribute across instances
        
        keepalive 64;  # Keep connections alive
    }

    # Rate Limiting
    limit_req_zone $binary_remote_addr zone=api_limit:10m rate=100r/s;
    limit_req_zone $binary_remote_addr zone=auth_limit:10m rate=10r/s;
    limit_conn_zone $binary_remote_addr zone=conn_limit:10m;

    # Main Server Block
    server {
        listen 80;
        server_name localhost;

        # Connection limits
        limit_conn conn_limit 20;

        # API Endpoints
        location /api/ {
            limit_req zone=api_limit burst=50 nodelay;
            
            proxy_pass http://sms_backend;
            proxy_http_version 1.1;
            
            # Headers
            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 "";
            
            # Timeouts
            proxy_connect_timeout 60s;
            proxy_send_timeout 60s;
            proxy_read_timeout 60s;
            
            # Buffering
            proxy_buffering on;
            proxy_buffer_size 4k;
            proxy_buffers 8 4k;
            proxy_busy_buffers_size 8k;
        }

        # Auth Endpoints (stricter rate limit)
        location /auth/ {
            limit_req zone=auth_limit burst=5 nodelay;
            
            proxy_pass http://sms_backend;
            proxy_http_version 1.1;
            
            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 30s;
            proxy_send_timeout 30s;
            proxy_read_timeout 30s;
        }

        # Health Check (no rate limit)
        location /health {
            proxy_pass http://sms_backend;
            proxy_http_version 1.1;
            
            proxy_set_header Host $host;
            proxy_connect_timeout 5s;
            proxy_send_timeout 5s;
            proxy_read_timeout 5s;
            
            access_log off;
        }

        # Web Panel
        location /panel {
            proxy_pass http://sms_backend;
            proxy_http_version 1.1;
            
            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 Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";
        }

        # Static Files
        location /static {
            proxy_pass http://sms_backend;
            proxy_http_version 1.1;
            
            # Caching for static files
            proxy_cache_valid 200 1d;
            proxy_cache_bypass $http_pragma $http_authorization;
            add_header X-Cache-Status $upstream_cache_status;
            
            expires 1d;
            add_header Cache-Control "public, immutable";
        }

        # Swagger Documentation
        location /swagger {
            proxy_pass http://sms_backend;
            proxy_http_version 1.1;
            
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        }

        # Default location
        location / {
            proxy_pass http://sms_backend;
            proxy_http_version 1.1;
            
            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;
        }

        # Custom error pages
        error_page 502 503 504 /50x.html;
        location = /50x.html {
            return 503 '{"success":false,"message":"Service temporarily unavailable","error":"maintenance"}';
            add_header Content-Type application/json;
        }
    }

    # Metrics endpoint (optional - for Prometheus)
    server {
        listen 9113;
        server_name localhost;
        
        location /metrics {
            stub_status on;
            access_log off;
            allow 127.0.0.1;
            allow 172.16.0.0/12;  # Docker network
            deny all;
        }
    }
}