Getting Rancher running on Google Cloud with Cloud SQL is a pain. Any tips?

I’ve been trying to get a HA Rancher setup going on Google Cloud without running it in Container Engine. All I want to do is set up an Instance Group that keeps a couple of Rancher servers running, and that bit of the setup works fine. The trouble comes when you want to connect it to a MySQL database.

I can’t figure out how to connect to the Cloud SQL instance from Rancher. I’ve tried running the Cloud SQL proxy docker image alongside it, and that connects, but I can’t figure out how to connect to that image from the Rancher image. I can’t connect directly without the proxy a) because of Google’s stupid separation of Cloud SQL from your instances, and b) you have to add every server’s IP manually if you want to connect that way.

As an alternative I’ve also tried setting up a DB via Compose.com, which is a HA setup and it fails to import/migrate the Rancher database.

Is there a simple way to set Rancher up with an external DB on Google Cloud, or will I have to settle for running a single instance with a mounted volume for backups?

Update: I did eventually get this working, but it doesn’t run particularly well with Google’s overzealous firewall rules and various other fudgings. I’ve got it running elsewhere for now with agents running on GCP.