You built a chat app on Cloudflare Workers. Fast, cheap, serverless. Launch day arrives.
Two users open the same chat room. Their messages go to random Workers instances scattered across the globe. The instances share nothing. User A's message never reaches User B. The chat room is broken.
You bolt on Redis. Now you're managing a cluster. Then a WebSocket server. Then sticky sessions. Then a message queue. You came for serverless. You got a distributed systems degree.
Durable Objects are the fix.
One object. One name. getByName("room-42"). Every user in that room — anywhere in the world — gets routed to the same running instance. It holds the messages in memory, persists them to a built-in SQLite database, broadcasts to every connected WebSocket, then hibernates when the room goes quiet. Wakes up the instant someone types again.
No Redis. No sticky sessions. No queue. No ops.
Use it when your problem is coordination — when two or more users or processes need to agree on shared state in real time.
Chat rooms. Collaborative docs. Multiplayer games. AI agents with long-running memory. Anything where "which server handles this?" used to be a hard question.
If your users never need to talk to each other through your backend, you don't need it. If they do, it's the cleanest solution that exists at the edge today.