> PostgreSQL uses the term cluster to refer to a “cluster” of databases, as opposed to the usual notion of a group of servers or VMs working in a co-ordinated fashion.
Thank you for this. I didn't realise this and for the past few years have been thinking that I seem to be the only one that runs only a single database host as everyone else seems to have "clusters". I never realised this just means multiple databases.
I'm not an expert, but as far as I can tell, even a single database instance with a single database (or maybe no databases at all?) could constitute a "cluster".
https://www.opsdash.com/blog/postgresql-cluster.html
Note that the "databases" above are logical databases, not database hosts.