websocket-engineer

WebSocket Engineer

Core Workflow

1. Analyze requirements — Identify connection scale, message volume, latency needs
2. Design architecture — Plan clustering, pub/sub, state management, failover
3. Implement — Build WebSocket server with authentication, rooms, events
4. Validate locally — Test connection handling, auth, and room behavior before scaling (e.g., npx wscat -c ws://localhost:3000); confirm auth rejection on missing/invalid tokens, room join/leave events, and message delivery
5. Scale — Verify Redis connection and pub/sub round-trip before enabling the adapter; configure sticky sessions and confirm with test connections across multiple instances; set up load balancing
6. Monitor — Track connections, latency, throughput, error rates; add alerts for connection-count spikes and error-rate thresholds

Reference Guide

Load detailed guidance based on context:

Code Examples

Server Setup (Socket.IO with Auth and Room Management)

import { createServer } from "http";
import { Server } from "socket.io";
import { createAdapter } from "@socket.io/redis-adapter";
import { createClient } from "redis";
import jwt from "jsonwebtoken";

const httpServer = createServer();
const io = new Server(httpServer, {
  cors: { origin: process.env.ALLOWED_ORIGIN, credentials: true },
  pingTimeout: 20000,
  pingInterval: 25000,
});

// Authentication middleware — runs before connection is established
io.use((socket, next) => {
  const token = socket.handshake.auth.token;
  if (!token) return next(new Error("Authentication required"));
  try {
    socket.data.user = jwt.verify(token, process.env.JWT_SECRET);
    next();
  } catch {
    next(new Error("Invalid token"));
  }
});

// Redis adapter for horizontal scaling
const pubClient = createClient({ url: process.env.REDIS_URL });
const subClient = pubClient.duplicate();
await Promise.all([pubClient.connect(), subClient.connect()]);
io.adapter(createAdapter(pubClient, subClient));

io.on("connection", (socket) => {
  const { userId } = socket.data.user;
  console.log(`connected: ${userId} (${socket.id})`);

  // Presence: mark user online
  pubClient.hSet("presence", userId, socket.id);

  socket.on("join-room", (roomId) => {
    socket.join(roomId);
    socket.to(roomId).emit("user-joined", { userId });
  });

  socket.on("message", ({ roomId, text }) => {
    io.to(roomId).emit("message", { userId, text, ts: Date.now() });
  });

  socket.on("disconnect", () => {
    pubClient.hDel("presence", userId);
    console.log(`disconnected: ${userId}`);
  });
});

httpServer.listen(3000);