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Realtime Tech Notes

1. WebSockets

WebSockets provide a persistent, bidirectional connection between client and server.

What Makes WebSockets Different

  • Unlike HTTP, the connection stays open.
  • Both sides can send messages at any time.
  • Great for chat, live updates, collaboration, and gaming.

Core Ideas

  • client initiates the connection
  • server accepts the upgrade
  • connection remains open until closed
  • messages are framed efficiently

Common Uses

  • chat apps
  • live notifications
  • collaborative editing
  • dashboards
  • multiplayer games

Important Notes

  • use ws:// for insecure connections
  • use wss:// for secure connections
  • authenticate early in the connection lifecycle
  • handle disconnects and reconnections gracefully

2. Socket.IO

Socket.IO is a higher-level realtime library built on top of WebSocket-like transport with fallbacks and extra features.

Why People Use It

  • easier event-based API
  • automatic reconnection
  • fallback transports
  • rooms and namespaces
  • acknowledgment support

Rooms

  • Rooms are logical groups of sockets.
  • Useful for chat rooms, live sessions, and shared channels.
socket.join("room1");
io.to("room1").emit("message", "Hello room");

Events

  • Socket.IO uses named events for communication.
  • You emit and listen for custom events.
socket.emit("message", data);
socket.on("message", handler);

Auth

  • Authenticate the socket connection before joining sensitive rooms.
  • Common approaches include token-based auth during handshake.

Socket.IO Best Practices

  • namespace your events clearly
  • validate payloads
  • handle disconnects
  • clean up listeners
  • don’t trust client data blindly

3. Pub/Sub and Redis Intro

Pub/Sub means publish and subscribe.

Basic Idea

  • A publisher sends a message to a channel.
  • Subscribers listening to that channel receive the message.

Why It Matters

  • useful for realtime fan-out
  • helps when multiple app servers need to share events
  • often used with sockets and background jobs

Redis Intro

  • Redis is often used as a Pub/Sub broker.
  • It can also support caching, sessions, queues, and rate limiting.

Practical Notes

  • Pub/Sub messages are transient unless backed by persistence elsewhere.
  • It is good for live event distribution, not durable message storage.