Glossary

Review the definitions for terms used across Cloudflare’s Durable Objects documentation.

Term	Definition
Durable Objects	The product name, or the collective noun referring to more than one Durable Object instance.
Namespace	A container for a collection of Durable Objects that all share the same Durable Object (class) definition. A single Namespace can have (tens of) millions of Durable Objects. Metrics are scoped per Namespace.
Durable Object	An individual Durable Object. A Durable Object is globally unique (referenced by ID), provides a global point of coordination for all methods/requests sent to it, and has private, persistent storage that is not shared with other Durable Objects within a Namespace.
Stub	An object that refers to a unique Durable Object within a Namespace and allows you to call into that Durable Object via RPC methods or the fetch API. For example, let stub = env.MY_DURABLE_OBJECT.get(id)
actor	A term referring to a unique Durable Object.
instance	See 'actor'.
Durable Object class	The JavaScript class that defines the methods (RPC) and handlers (fetch, alarm) as part of your Durable Object, and/or an optional constructor. All Durable Objects within a single Namespace share the same class definition.
Storage Backend	By default, a Durable Object class can use Storage API that leverages a key-value storage backend. New Durable Object classes can opt-in to using a SQLite storage backend.
Storage API	The transactional and strongly consistent (serializable) Storage API for persisting data within each Durable Object instance. State stored within a unique DO instance is "private" to that Durable Object, and not accessible from other Durable Objects. Storage API includes key-value (KV) API, SQL API, and point-in-time-recovery (PITR) API. Durable Object classes with the key-value storage backend can use KV API. Durable Object classes with the SQLite storage backend can use KV API, SQL API, and PITR API.
KV API	API methods part of Storage API that support persisting key-value data.
SQL API	API methods part of Storage API that support SQL querying.
Migration	A Durable Object migration is a mapping process from a class name to a runtime state. Initiate a Durable Object migration when you need to: Create a new Durable Object class. Rename a Durable Object class. Delete a Durable Object class. Transfer an existing Durable Objects class.
Alarm	A Durable Object alarm is a mechanism that allows you to schedule the Durable Object to be woken up at a time in the future.