durable-objects

Extend the DurableObject class from cloudflare:workers and configure new_sqlite_classes in your wrangler migrations. Initialize tables inside the constructor using ctx.blockConcurrencyWhile and this.ctx.storage.sql.exec for synchronous SQL queries.

Use @cloudflare/vitest-pool-workers to run tests inside the Workers runtime. Access stubs via env from cloudflare:test, inspect internals with runInDurableObject, and trigger alarms immediately with runDurableObjectAlarm.

Use Durable Objects when you need coordination, strong consistency, per-entity storage, or persistent WebSocket connections, such as chat rooms or booking systems. Plain Workers are better for stateless request handling and maximum global distribution.

No, PRAGMA user_version is not supported in Durable Objects SQLite storage. Track schema versions in a dedicated _sql_schema_migrations table and apply incremental migrations during constructor initialization.

blockConcurrencyWhile blocks all concurrency in the instance, so using it on every request caps throughput at roughly 200 requests per second. Reserve it for one-time initialization and never hold it across fetch or external I/O.

Each Durable Object supports one alarm at a time, and calling setAlarm replaces any existing alarm. The alarm handler runs at the scheduled time with automatic retries on failure, so handlers should be idempotent and can reschedule themselves.