"In addition to continuous protection which is explained above, high availability is available if your application requires less exposure to downtime. We provision stand-bys if you select high availability at provisioning time. This can be for your primary node, or for your distributed nodes."
https://docs.citusdata.com/en/v6.1/cloud/features.html
Please let me know if I've missed any resources on this topic!
Yep, our docs are definitely behind the product here, we'll be working to improve. FWIW it would be the closest to the Heroku Postgres HA as it's the same person that wrote both systems.