Private Network Fails

Question

I have 4 services the fourth one is nginx reverse-proxy.

Two services are dockerized, the other service is straight nodejs.

Now the NodeJs works well, I call the service name with a port number, but calling the other two dockerized fail. I tried entering the whole DNS ```api.railway.internal``` but it doesn't work.

What should I do?

I am using NGINX, so here is basic config I want to achieve

```bash
upstream api_service {
    server api.railway.internal:5000 fail_timeout=120;
}
```

Then I can use it in a location block

```bash
location /api {
    proxy_pass http://api_service
}
```