Every machine reports its own name as localhost

Asking any machine in the estate for its own fully-qualified name returned localhost instead of its real name.

This affects anything that identifies a machine by asking it who it is — logs, monitoring, mail headers, and clustered software that registers itself by name.

Cause

The machine's own name had been appended to the loopback line in its hosts file. A name lookup returns the first name on a matching line, so the machine's real name was permanently shadowed by localhost. The configuration automation was writing that line itself, so the fault was reapplied on every run and would have returned even after a manual fix.

Fix

Corrected on every machine, and the automation split into two separate entries so the loopback name and the machine's own name can no longer collide. Care was taken to keep localhost resolvable, because the cluster's own health checks depend on it.