App Engine and Firebase Hosting in One Domain

Question

I have a custom domain (travelbox.id) that connected to Firebase Hosting already. I also have an App Engine application to serve as my API. I want to host the App Engine application on api-dev.travelbox.id. I mapped the custom domain to App Engine following this docs but domain connection to Firebase Hosting stop working. If you access api-dev.travelbox.id it is connected to App Engine. But if you access travelbox.id it doesn't connected to Firebase Hosting.

Is that impossible to achieve what I want?

Answer 1

I had the same issue and contacted Google Cloud support, here's their answer:

App Engine doesn't need to have the A records on the root domain if you are only serving from a subdomain. App Engine should work properly for you with just the one CNAME on subdomain.example.com.

Answer 2

I found the solution myself, here you go!

On the fourth step in this docs, i didn't add A records, just add AAAA records. Suprisingly, it works! :D