I also found that it's easier to launch an Elastic Beanstalk Docker app with a Postgres RDS instance. I'm hoping Google's Flexible Environment will address this, but I was not able to get it to deploy. To be fair, I only tried for a bit yesterday and gave up.

It'd be great if you can share how to best spin up a managed Postgres instance.

I'm using GKE and it has been working like a charm so far.