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Bernard Baker
Bernard Baker

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Maintain state in Serverless

Workers Durable Objects Beta: A New Approach to Stateful Serverless

What is a "Durable Object"?

I'm going to be honest: naming this product was hard, because it's not quite like any other cloud technology that is widely-used today. This proverbial bike shed has many layers of paint, but ultimately we settled on "Unique Durable Objects", or "Durable Objects" for short. Let me explain what they are by breaking that down:

Objects: Durable Objects are objects in the sense of Object-Oriented Programming. A Durable Object is an instance of a class -- literally, a class definition written in JavaScript (or your language of choice). The class has methods which define its public interface. An object is an instance of this class, combining the code with some private state.

Unique: Each object has a globally-unique identifier. That object exists in only one location in the whole world at a time. Any Worker running anywhere in the world that knows the object's ID can send messages to it. All those messages end up delivered to the same place.

Durable: Unlike a normal object in JavaScript, Durable Objects can have persistent state stored on disk. Each object's durable state is private to it, which means not only that access to storage is fast, but the object can even safely maintain a consistent copy of the state in memory and operate on it with zero latency. The in-memory object will be shut down when idle and recreated later on-demand.

What can they do?

Durable Objects have two primary abilities:

Storage: Each object has attached durable storage. Because this storage is private to a specific object, the storage is always co-located with the object. This means the storage can be very fast while providing strong, transactional consistency. Durable Objects apply the serverless philosophy to storage, splitting the traditional large monolithic databases up into many small, logical units. In doing so, we get the advantages you've come to expect from serverless: effortless scaling with zero maintenance burden.

Coordination: Historically, with Workers, each request would be randomly load-balanced to a Worker instance. Since there was no way to control which instance received a request, there was no way to force two clients to talk to the same Worker, and therefore no way for clients to coordinate through Workers. Durable Objects change that: requests related to the same topic can be forwarded to the same object, which can then coordinate between them, without any need to touch storage. For example, this can be used to facilitate real-time chat, collaborative editing, video conferencing, pub/sub message queues, game sessions, and much more.

How exciting 😁 and just what I needed when I migrated a database and had to reimplement GraphQL service.

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