Hi @KDSys
Thank you.
I added the rules in backend droplet but i think that it cannot retrieve the source IP address.
My code

Frontend droplet nginx conf
upstream web_site {
    server localhost:4000;
}
server {
    listen 80;
    server_name mydomain;
    location / {
        proxy_pass http://web_site;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_http_version 1.1;
        proxy_set_header X-NginX-Proxy true;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection 'upgrade';
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
         proxy_redirect off;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Backend droplet nginx conf inside docker container

upstream web_site {
  ip_hash;
  server web:8000;
}

server {
    listen 80;
    server_name api.mydomain.com;
    location / {
        satisfy any;
       allow frontend droplet ip;
        deny all;
        return 301 https://$host$request_uri;
    }
    location /.well-known/acme-challenge/ {
         root /var/www/certbot;
    }
}

server {
    listen 443 ssl;
    server_name api.mydomain.com;


    location / {
          satisfy any;
       allow frontend droplet ip;
        deny all;
        proxy_pass http://web_site/;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $host;
        proxy_redirect off;
    }


}

it blocks all ips.

Thank you in advance