The moment a feature needs to update live, a live counter, a presence indicator, a "new message" badge, an activity feed, the reflex is to reach for a websocket service. Pusher, Ably, a Socket.IO server, a stateful Node process parked next to your stateless app. That is one more thing to deploy, scale, secure, and pay for, and it exists mostly to move small events from one place to a bunch of connected browsers.
If your data already lives in Postgres, you already have a message bus for that. Postgres ships with LISTEN and NOTIFY, a lightweight publish/subscribe system built into the database. Pair it with server-sent events from a serverless function and you can fan realtime updates out to every connected client without standing up any realtime infrastructure at all. In this post I build exactly that on a Neon Function, explain the one part that is subtle on serverless, and prove it works with two live subscribers. The repo is at the end.
TL;DR
Postgres LISTEN/NOTIFY is a built-in pub/sub. NOTIFY channel, 'payload' delivers to every connection that has run LISTEN channel.
A serverless function holds each browser's SSE connection open and keeps one Postgres LISTEN connection. On a write, the app calls pg_notify, and every isolate pushes the event to its SSE clients.
