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Real-time Chat Backend (WebSocket)

In short

A chat backend that works on one server is a tutorial. One that keeps rooms, history and online status working across many servers is a portfolio project.

A more complete real-time backend than the earlier practice project — supporting multiple rooms, message history, presence, and horizontal scaling via Redis pub/sub.

The purple blob talks into a walkie-talkie while friends in other rooms hear it.

Think of it like this

Walkie-talkies in the hostel

Once everyone's walkie-talkie is on the same channel, anyone can talk and everyone hears it instantly, no dialling each time. A WebSocket is that always-open channel between each phone and your server.

Watch it happen

Riya messages Kabir, who's on another server

Riya

Server A

Redis pub/sub

Server B

message → room cse

1/6Riya's phone sends the message over its open WebSocket to Server A.

The big ideas

What you need to know

Rooms and history

Users join rooms. Messages are saved, and older history loads with cursor pagination as you scroll up.

Presence

Track who's online with heartbeats and short Redis TTLs, so a dropped phone goes offline on its own.

Scale with pub/sub

Sockets stick to one server. A Redis pub/sub adapter lets a message reach users on every server.

Delivery and acks

Acknowledge saved messages and let clients retry with a client-generated ID, so retries don't duplicate.

See it in code

Walk through the code

1import { Server } from "socket.io";2import { createAdapter } from "@socket.io/redis-adapter";3import { createClient } from "redis";4 5const pub = createClient({ url: process.env.REDIS_URL });6const sub = pub.duplicate();7await Promise.all([pub.connect(), sub.connect()]);8const io = new Server(3000, { adapter: createAdapter(pub, sub) });9io.on("connection", (socket) => {10  socket.on("join", (room: string) => socket.join(room));11  socket.on("message", async ({ room, text }, ack) => {12    const saved = await saveMessage(room, socket.data.userId, text); // DB first13    io.to(room).emit("message", saved); // reaches sockets on every server14    ack({ id: saved.id });15  });16});