Hi!
You seem to be on the right track. If you are using an external Postgres instance tho, I’d say remove all references to the postgres service from the dockes-compose.yml file and the install.sh script.
Seems like the install script has a bug with --no-user-prompt flag: https://github.com/getsentry/onpremise/issues/665. For now, just set the CI env variable to 1 to make it non-interactive.
Once you reach the setting up databases step, it should continue with the migrations. The warning you shared is harmless and irrelevant.
The issue might be a timeout or slow connection to your RDS instance if it seems to be stuck with no more output.