OpenTofu 1.9: for_each in the provider block

https://opentofu.org/docs/intro/whats-new/#provider-iteration-for_each

variable "regions" {
  description = "A list of regions."
  type        = set(string)
}

provider "aws" {
  alias    = "by_region"
  region   = each.value
  for_each = var.regions
}

module "deploy" {
  source    = "./deploy"
  providers = {
    aws = aws.by_region[each.key]
  }
}

#OpenTofu