I’ve deployed a full-stack application on Railway consisting of the following:

• A Convex backend

• A Next.js 15 frontend

• A Node.js backend API

All three services deploy successfully and work individually:

• Convex dashboard loads properly via a custom domain.

• Next.js app and Node backend are reachable via custom domains.

• All environment variables are configured in the Railway dashboard.

  However, I’m running into issues with internal service-to-service communication post-deployment:

• Environment variables appear undefined at runtime

  • NEXT_PUBLIC_CONVEX_URL is defined in the Railway dashboard under the frontend service.

  • However, at runtime in the browser, it is undefined, even though it’s prefixed correctly.

  • It references a private internal domain of the Convex service.

  • I’ve confirmed the variable exists before deployment, and it’s added before the build step.

• Internal requests between services fail

  • The Node.js backend tries to connect to Convex or respond to frontend calls, but fails.

    I've tried sending a request from Postman using a public custom domain. I've received the following error.

  • Example error:
    [cause]: Error: connect ECONNREFUSED fd12:fe40:....

    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1611:16) {

    errno: -111,

    code: 'ECONNREFUSED',

    syscall: 'connect',

    Jun 17 00:19:41

    address: 'fd12:fe40:9a...',

    port: 443

    }

    }

  • Custom domains don’t solve internal connectivity

    • I’ve mapped custom domains for the frontend and backend.

    • External traffic works (I can hit the routes via browser or Postman).

    • Internal service-to-service requests still fail or time out.

What I've tried
1. Tried binding servers to both 0.0.0.0 and ::,as the private network is an IPv6 only network.

Questions:

• How to ensure internal networking between services works on Railway?

• Why is NEXT_PUBLIC_CONVEX_URL undefined at runtime, even when it exists in Railway variables?

• What’s the recommended way to structure internal service-to-service communication for multi-service setups (Convex + Node + Next) on Railway?