I just tried out the “app resource” and when running locally in go (but I presume this applies to any language) the resource URL that is available in the environment is not able to connect as most clients presume SSL by default and the resource does not support it (even with the encrypted option, which I would like to use in production).
Ideally the local resource should append the ?sslmode=disable-parameter to the URL.
Or even better would be to append that when not encrypted, and with the encrypted-option enabled actually support SSL connections even on the local resource. This way it would match the RDS one perfectly and potentially catch some SSL cert issues that can otherwise only be found in production.