I have encountered what seems like a bug in aws.rds.Cluster, at least with Aurora and in Python. If you specify an engine_version of, say '5.7' it will happily create the cluster for you. But from that point on, on any update it thinks that the cluster version has changed and tries to update it, and the update fails because the resource says that you cannot change to the same version. It seems to only work properly if a fully qualified version string is supplied; e.g., '5.7.mysql_aurora.2.07.1'

Mind opening a bug on Github at https://github.com/pulumi/pulumi-aws ?

sure