Firebase custom domain deploy - firebase-hosting

Question

I'm trying to deploy applications to different custom domains under one Firebase hosting site. E.g., I want to deploy one app to app.domain.com, and another to just domain.com.
My custom domains were setup and connected correctly, but when trying to deploy I kept getting a 404 via the cli. I could not quite figure out what to put as the hosting targets, or if it was actually even possible. Here was my hosting config:
// .firebaserc:
"hosting": {
"app": [
"app.domain.com"
],
"public": [
domain.com"
]
}
// firebase.json:
"hosting": [
{
"target": "app",
"public": "./dist/apps/app",
"ignore": [
"firebase.json",
"**/.*",
"**/node_modules/**"
]
},
{
"target": "public",
"public": "./dist/apps/public",
"ignore": [
"firebase.json",
"**/.*",
"**/node_modules/**"
]
}
],
That did not work. I can see how only using custom domains in the .firebsaerc does not explicitly tie the hosting site to the deployment, but, those custom domains can only be used once across all sites.
It only worked after I created another site (now have 2), then in .firebaserc, added one site as the app target, and the other for the public target. I could visit the two domains and the different apps were being served at this point.
The final .firebaserc looked like this:
"hosting": {
"app": [
"domain-site-1"
],
"public": [
"domain-site-2"
]
}
Is it possible to deploy unique assets to different custom domains under 1 site? It feels like this should be possible, but I must be missing something.

Answer 1

A Firebase site servers the same resources to all domains pointing to it. If you want different domains to server different resources than you must create multiple sites and point the different domains to the different sites.