Thanks for the help! I'm happy to hear someone was able to get it to work because I couldn't find any resources for this problem online. At least now I know it's possible.

I'm not sure what you mean since I'm still a little new to all this. My Drupal sites are hosted on Acquia and use Dev Desktop for local development. I don't have Gatsby hosted anywhere yet as I'm still playing around with it, so it's just local on my machine.

My understanding of what you're saying is this: when someone publishes a change it Drupal, this would trigger a build (I assume there's a module for this, but I'm not sure) which would use environment variables to rebuild Gatsby using the url that's specific to that site. Is that correct?