Consider this wording. It also uses “good practice”.
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It is good practice to limit the number of superuser roles that exist in a cluster to exactly one: the inevitable bootstrap superuser. This recognizes the fact that, once the initial configuration of a cluster has been done immediately after its creation (which configuration is done while still in self-imposed single-user mode), there are then very few, and infrequent, tasks that require the power of the superuser role.
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Nobody supports it!
I’m puzzled why the good practice statement about a role with the CREATEDB and CREATEROLE attributes earns a place in the doc while nobody at all is prepared to make a practice statement about how many superusers is good. I’d like very much to understand the critical parts that I’m missing of the essential mental model in this general space.
My policy would be that no one is supposed to login to the database cluster using the postgres role. Period. Upon initialization whomever is responsible for creating the cluster gets their personal user credentials installed into the cluster as superuser and from that point on never uses postgres. They will, however, in the interest of business continuity, create additional superusers for any others who share the superuser responsibility.
In short, there is very little room to argue against the principle of least privilege. I don't see where that principle supports "only have one superuser" nor does it seem better than another security principle: "everyone must have their own credentials".
I suppose the suggestion I would be willing to consider is: only have the postgres superuser, never grant superuser to login roles explicitly, instead if those persons require superuser grant them membership in the postgres role. Except I don't think that actually works in a desirable way today. Having multiple roles in service of least-privilege while retaining users must use personal login credentials is my suggested starting point absent some more improvements in the authorization systems (or a better understanding of existing ones by your truly).
So yes I, like everyone else, is going to end up forming their own generalities. Ideas that I cannot wholly discredit as bad, but that don't fit into my generality, get the "if the specific circumstances warrant it" treatment. My own presuppositions ultimately should get the same treatment by whomever is implementing such policies.
David J.