Keep in mind that private networking is not available during the build phase.

I saw that page it doesnt not mention an internal DNS server for resolving hostnames, I do not have a way to disable the resolver.

it needs an DNS server address ex: 1.1.1.1:53 but for resolving the local railway private domains

You don't need to set one, the resolver available to the system is already capable of resolving private domains.

There is no way to disable the manual resolver and their proxy isnt listed in github to fork it.

it was designed for docker and to use the docker engine dns to resolve the hostname for containers, but I had to adapt it to railway

Then use fd12::10 but this address is provided with zero assurances, you should essentially assume this address will change at some point in the future.

Is there an ipv4 address for this?

No

Okay I will see if they can come up with a way to disable to resolver then,

if I remove the resolver variable I get the following error:

2026/04/12 04:26:42 [error] 32#32: recv() failed (111: Connection refused) while resolving, resolver: 127.0.0.11:53