Most small systems, an LGU records app, a clinic intake system, a school portal, serve hundreds of concurrent users at most. That load fits comfortably on one well-run VPS, and the simplicity is the point.
One box means one thing to patch, one thing to back up, one place to look when something's wrong. A cluster multiplies all of that by the node count, for reliability gains a small team can't operate.
The architecture that makes one box enough: Postgres on the same host, a reverse proxy handling TLS, automated off-site backups, and a documented rebuild path. If the box dies, you restore to a fresh VPS in an afternoon.
Scale up when the numbers say so, not before. Vertical headroom on a single VPS covers years of growth for most small systems, and the day it doesn't, you'll have the usage data to scale deliberately.
