database isn't hard to have HA with, it's actually very easy to do any of this.

i already design with Auto Scale Group in mind, we run it in spot instance which tend to be much cheaper. Spot instances can be reclaimed anytime, so you need to keep this is kind.

I also have data blobs which are memory maped files, which are swapped with no downtime by pulling manifest from GCS bucket each hour, and swapping out the mmaped data.

i use replicas, with automatic voting based failover.

I've used mongo with replication and automative failover for a decade in production with no downtime, no data lost.

Recently, got into postgres, so far so good. Before that i always used RDS or other managed solution like Datastore, but they cost soo much compared to running your own stuff.

Healthchecks start new server in no time, even if my Hertzner server goes out or if whole Hertzer goes out, my system will launch digital ocean nodes which will start soaking up all requests.