Can’t reach Next.js service from other containers using internal URL (only works with public URL)

Question

I’m running a project on Railway with three services: **Next.js**, **NestJS**, and **Nginx**.

I’m facing an issue where I **cannot reach my Next.js server from other services using the internal URL**. If I use the **public URL**, everything works fine, but internal connections fail.

* When I try to reach Next.js from Nginx, I get a **502 Gateway Error**.
* I tested my Nginx configuration and it looks correct.
* When I `curl` from inside another container, the request succeeds with the public domain, but fails with the internal hostname/URL.

I’m using the official Next.js Docker template from Vercel:  
  
<https://github.com/vercel/next.js/blob/canary/examples/with-docker/Dockerfile>

It seems like the Next.js container isn’t accessible internally, only externally through Railway’s public proxy.