here’s how simple it is to avoid putting resources from the bad us-east1 AZ

good_zone_ids.tf

data "aws_availability_zones" "good_zone_ids" {
  exclude_zone_ids = [
    # There are no modern instance types in use1-az3; AWS has left
    # that zone behind for the most part.  See, for example, here:
    # https://www.reddit.com/r/aws/comments/g5lh7h/t3m5r5_instance_types_in_use1az3/
    "use1-az3",
  ]
  state = "available"
}
output "good_zone_ids" { value = data.aws_availability_zones.good_zone_ids }

data "aws_subnet_ids" "private_subnets" {
  vpc_id = data.aws_vpc.vpc_id.id

  filter {
    name   = "tag:Name"
    values = var.subnet_filter
  }
  filter {
    name   = "availability-zone-id"
    values = data.aws_availability_zones.good_zone_ids.zone_ids
  }
}
output "private_subnets" { value = data.aws_subnet_ids.private_subnets }