The following video was shared by @Gordypls. So HT to him.
Ive seen similar solutions to this need come and go over the years and have never found a solution that I was entirely happy with. This one looks better than other contenders. Its a 4 minute watch and feels like a reasonable solution for use on AWS.
Ive corrected the title on this video because CIFS is a legacy name now. See this.
via Qantas: Building a Highly-Available, Multi-AZ CIFS Cluster on AWS – YouTube