WebSocket
Also known as:
WebSockets
WS Protocol
Definition
A WebSocket is a persistent, full-duplex connection between a client and a server over a single TCP connection. After an HTTP handshake upgrades the connection, both sides can send messages at any time without opening new requests. This makes it the standard choice for real-time apps like chat, live dashboards, multiplayer games, and collaborative editors.
Key Takeaways
- Unlike normal HTTP, a WebSocket stays open, so the server can push data to the client instantly without polling.
- It is full duplex. Client and server can both send at once, which HTTP request-response cannot do.
- Compared to long polling and server-sent events, WebSockets add bidirectional messaging at the cost of more connection state to manage.
- Millions of open connections need careful capacity planning, sticky routing, and a way to fan messages out across servers.
How It Works
- The client sends an HTTP request with an Upgrade header asking to switch to the WebSocket protocol.
- The server agrees, and the same TCP connection is now a two-way message channel.
- Either side sends framed messages until one closes the connection or a heartbeat ping fails.
- At scale, a pub/sub layer routes a message to whichever server holds the target client’s socket.
Where It Is Used
- Slack, Discord, and WhatsApp Web keep a WebSocket open for instant message delivery.
- Google Docs and Figma use persistent connections to sync edits between collaborators in real time.
- Trading and betting platforms push live prices to browsers over WebSockets.