The freight forwarders' portal shows “Service unavailable” at every login

Détroit Fret (a fictitious company) operates a dry port near Tangier. Its web portal lets freight forwarders track containers and pay storage fees. All applications use the PostgreSQL 16 database fret on pg-df-01.

Since 07:50, the portal answers “Service unavailable” and the API log is full of database connection errors. Nothing was deployed this weekend, except a new version of the billing batch on Friday evening. The on-call developer is already suggesting “set max_connections to 5000”.

Your mission: make the database reachable for the portal again, find who is consuming the connections, and put a safeguard in place to prevent a recurrence.