Basing secrets and env variables from other apps

I’m launching a few apps that need to talk to each other.

How would I set up toml files to reference each other’s internal URLs and/or env variables and hostnames?

To talk from one app to another you can use private networking. Simply reference an app via the <app-name>.internal hostname.

I have an example app called ancient-lake-6209 in my account:

root@4394454d:/# curl -sI ancient-lake-6209.internal
HTTP/1.1 200 OK
Server: nginx/1.23.3
Date: Tue, 21 Mar 2023 00:05:46 GMT
Content-Type: text/html
Content-Length: 615
Last-Modified: Tue, 13 Dec 2022 15:53:53 GMT
Connection: keep-alive
ETag: "6398a011-267"
Accept-Ranges: bytes

[adding to what @ben-io already sent]

It looks like you’re starting from scratch.
I’ll suggest spending sometime scanning though the fly docs (to at least see how to create and deploy apps)

After, head down to the Fly Reference for more information on almost every feature we provide at the moment.