Durable Objects

What it is

Think of a single front-desk clerk who handles one person at a time and remembers everyone who came before — no second clerk can give a conflicting answer. A Durable Object is that clerk in software: a tiny server that keeps its own memory (it is "stateful") and that Cloudflare guarantees exists in exactly one place at a time. Each object has a unique ID, its own permanent storage, and processes requests one at a time, so it's a natural home for coordination — counters, locks, game rooms, chat sessions. Where a Worker forgets everything between requests (it is "stateless") and runs everywhere at once, a Durable Object remembers and is singular.

Strengths

• Single-instance guarantee — no race conditions across replicas.
• Built-in persistent storage (now backed by SQLite) co-located with the object.
• Ideal for real-time apps: WebSockets (a live, two-way connection that stays open so the server can push updates instantly), presence, live collaboration.
• Strong consistency: read-after-write within an object is immediate.
• Alarms let an object schedule its own future work.

Trade-offs

• Single-threaded per object — a hot object can become a bottleneck; shard by key.
• More to reason about than a plain Worker; you design the object boundaries.
• Storage per object is bounded; not a substitute for D1 (a SQL database) or R2 (file storage) at scale.
• Overkill for stateless request handling.

When to use it

Reach for Durable Objects when you need coordination or per-entity state: chat rooms, multiplayer game state, rate limiters, leader election, or a live document that many clients edit at once.

Vibe coding fit

Durable Objects shine for the real-time features that are otherwise fiddly to build, and an agent can scaffold the class, the binding, and the WebSocket handling. Tell it how to shard — usually one object per room, user, or document — so a single object doesn't serialize all your traffic. The config below declares a Durable Object class with a migration.

# wrangler.toml
[[durable_objects.bindings]]
name = "ROOM"
class_name = "ChatRoom"

[[migrations]]
tag = "v1"
new_sqlite_classes = ["ChatRoom"]

npx wrangler deploy