I've put together a repo that will let you set up Node-RED on AWS running on multiple instances behind a load balancer - high availability for Node-RED on AWS in other words.
It works by sharing the filesystem between instances using EFS and doing some tricky flow reloading on each instance to catch changes. It uses Auth0 for login, and can be used with Projects. It's easy to set up via a couple of CloudFormation templates and some basic config.
If you need HA on AWS, please try it and see how you go.