durable-objects

Extend the DurableObject class from cloudflare:workers and initialize tables inside the constructor using ctx.blockConcurrencyWhile with ctx.storage.sql.exec. Configure the binding in wrangler.jsonc and add a migration with new_sqlite_classes listing your class name.

Add a durable_objects.bindings array mapping a binding name to your class_name, then declare a migrations entry with a tag and new_sqlite_classes. The Worker accesses the namespace via env.MY_DO and creates stubs with getByName or idFromString.

Use Durable Objects for coordination, strong consistency, per-entity storage, persistent WebSocket connections, or scheduled per-entity work like alarms. Avoid them for stateless request handling, maximum global distribution, or high fan-out independent requests.

Use Cloudflare's Vitest integration to run tests in the Workers runtime, covering RPC behavior, HTTP routing, instance separation, SQLite persistence, and alarms. Use the documented test helpers to trigger scheduled alarms without waiting for wall-clock time.

Durable Objects can be evicted or restarted, so any state held only in memory is lost. Always persist critical data to storage before updating in-memory caches, and ensure in-memory state is reconstructible from durable storage.

No, each Durable Object supports only one alarm at a time. Calling setAlarm replaces any existing alarm, so reschedule inside the alarm handler if recurring work is needed, or use deleteAlarm to cancel.