Disable parallel processing when using the for_each Meta-Argument

I used the for-each argument to provision a MariaDB Galera cluster. It creates three EC2 instances on AWS. Very simplified example below:

locals {
	db_servers = {"sun", "moon", "earth"}
}

resource "aws_instance" "dbserver" {
        for_each = local.db_servers
        instance_type = "t3.large"
}

One thing to watch out for with Galera Cluster is that you must always have at least 1 server in the cluster running at all times.

If I wanted to change the instance_type, how do I do so in such a way that the change is applied one instance at a time. More specifically, wait for the instance to be back online before attempting to chance the next one.