# A WebSockets tier for realtime

> Hold realtime connections open on a Realtime Hub that runs a runtime built for them, and route only realtime traffic to it, so chat and live updates stop eating App Server workers.

Give realtime traffic its own Hub, because a connection that stays open for minutes cannot share a worker pool with requests that last milliseconds.

## Move up when

- Realtime messages fail as refused, or App Server workers sit waiting on open connections.
- Chat or live updates arrive late while pages and reads are fine.
- After a restart, clients reconnect all at once and the Hub refuses half of them.

## The Design



The Load Balancer splits traffic by request kind. Realtime goes to the Hub and every other kind goes to the App Server. The Hub takes realtime and sends nothing on.

## Why it works

A runtime that holds a worker for each connection holds none, so the Hub refuses everything. An event loop or a green thread holds each connection for a few KB, so a Node.js Stack lets the Hub keep many open. Clustering lets bigger Hub sizes add room, and without it one box takes every connection and a larger size only adds Burn.

Presence earns more per message because social features pay for knowing who is online, and it spends CPU on every join. Reconnect backoff spreads a returning wave over time instead of refusing it.

## What it costs

A Hub is a stateful Node. A restart drops every connection and invites a reconnect wave, which is the [Reconnect storm](https://wiki.playquorum.dev/incidents/reconnect.md). Clustering needs a pub/sub backbone, and a split cluster loses the messages that cross the cut. The game has no long polling or server-sent events option, so it cannot show a cheaper fallback for light use.

## In Quorum

Place a [Realtime Hub](https://wiki.playquorum.dev/components/ws.md) and link it from a [Load Balancer](https://wiki.playquorum.dev/components/lb.md). Set the Link's kinds so only realtime reaches it. Research [WebSockets](https://wiki.playquorum.dev/research/websockets.md), and a runtime such as [Node.js](https://wiki.playquorum.dev/research/lang-node.md). The next rung, [sharding the database](https://wiki.playquorum.dev/patterns/shard-the-database.md), splits the data tier once one primary cannot take the writes.

Source: https://wiki.playquorum.dev/patterns/websockets-tier-for-realtime