Earlier quoted context omitted.
What does your reliability look like? Obviously no SLA but what can we really expect? Pay tier available for HA?
https://ntfy.sh/docs/faq/#what-are-the-uptime-guarantees I guarantee for nothing, since this is a spare time project. That said, I have had zero outages in 11 months, see https://ntfy.statuspage.io/ When it outgrows the single EC2 instance, I'll likely start building some distributed thingy to spread the load and do some HA things (sounds like fun). Probably just a load balancer and 2-3 instances with a rqlite backen…
rqlite will give you HA, but won't help with load (rqlite replicates for reliability, not for write performance). But I like to think the it'll give you solid -- and simple to use -- HA. Replicated just replaced their use of Postgres with rqlite for this reason[2].
[1] https://github.com/rqlite/rqlite
[2] https://www.replicated.com/blog/app-manager-with-rqlite/