کانفیگ nginx به‌عنوان Load Balancer (پخش بار روی چند سرور)

upstream app_cluster {
    server 10.0.0.11:3000 weight=3 max_fails=3 fail_timeout=30s;
    server 10.0.0.12:3000 weight=2 max_fails=3 fail_timeout=30s;
    server 10.0.0.13:3000 backup;      # فقط وقتی بقیه از کار افتاده‌اند
    keepalive 32;
}

upstream app_cluster {
    least_conn;          # سرور با کمترین اتصال فعال
    # ip_hash;           # هر کاربر همیشه به یک سرور (session چسبنده)
    # hash $request_uri consistent;   # توزیع بر اساس آدرس (مناسب کش)
    server 10.0.0.11:3000;
    server 10.0.0.12:3000;
}

server {
    listen 80;
    server_name app.example.com;

    location / {
        proxy_pass http://app_cluster;
        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 Connection "";

        proxy_next_upstream error timeout http_502 http_503 http_504;
        proxy_next_upstream_tries 2;
        proxy_connect_timeout 3s;
    }
}

log_format upstream_log '$remote_addr - $request [$status] $upstream_addr $upstream_response_time';
access_log /var/log/nginx/app.access.log upstream_log;

# در server block
add_header X-Upstream $upstream_addr always;

for i in $(seq 1 12); do curl -s -o /dev/null -D - https://app.example.com | grep -i x-upstream; done
awk '{print $5}' /var/log/nginx/app.access.log | sort | uniq -c

upstream app_cluster {
    server 10.0.0.11:3000;
    server 10.0.0.12:3000 down;   # موقتاً خارج از سرویس
}