I admit, I haven’t personally tried this in a multi-region deployment, but is it safe to assume the retry_joinprovider= approach is not working for you? It seems like it should. The cloud-auto-join docs show that a region setting is available. Did you see all that documentation already?
I believe that depends on the go-discover library. I’m sorry say this, but as best as I can tell, it doesn’t support specifying multiple regions.
That said, are you really trying to failover to a different cloud provider region? I ask because the region the the cloud auto-join provider setting relates to the cloud provider region (e.g. AWS us-east) not the Nomad region. I apologize, but I’m not sure I understand your use case fully yet.