Same stateful trick, now with your own infrastructure
We've got good news for developers who are enamored with Cloudflare Workers and Durable Objects but don’t want to be tied into that company’s backend infrastructure. Last week, Node.js creator Ryan Dahl unveiled his latest project, celld, which he described on X as “a self-hosted, distributed Durable Objects and Workers implementation.”
Dahl’s celld model is compatible with Cloudflare’s Workers and Durable Objects’ JavaScript APIs, but he claims that it is much less expensive to run.
The project is no mere budget-minded open source rip. On celld’s web page, Dahl and his team characterize their replication of the Durable Objects architecture as a “love letter.”
Cloudflare’s Durable Objects is a single-threaded object with a unique global ID and its own storage, where user data is stored in its own copy of SQLite. It runs on the Cloudflare serverless Workers runtime, which runs apps embedded in isolates —a type of lightweight virtual machine supported by Google's V8 JavaScript engine.
First devised by Kenton Varda and Cloudflare, Durable Objects is “one of the best primitives distributed systems has been handed in years,” celld’s creators write. Unlike traditional serverless platforms like AWS Lambda, the Durable Objects model co-locates the data with compute, while using single-threaded execution to eliminate complex concurrency issues.
“A primitive this good deserves to run anywhere,” the celld page states.
Serverless but stateful
Since its introduction in 2020, Durable Objects has been used to build low-latency, highly distributed Web applications. It is a stateful serverless execution environment, a data cache that can also do computation.
Using the WebSocket API, the Durable Object can connect many simultaneous users at once in a live environment. WebSockets’ Hibernate mode can put the object to sleep, so cloud bills don’t accrue when no one uses the app.
As a result, the stateful serverless model is best suited for real-time collaborative applications, such as multi-player games, team productivity apps and AI agents. Cloudflare uses Durable Objects for its serverless SQL service and AI Gateway.
One YouTube tutorialist explained that using Durable Objects allowed him to eliminate an entire stack of tools (Amazon API Gateway, Apache Kafka, Redis, AWS Lambda and EventBridge, Apache Airflow and Spark all get name-dropped) because Durable Objects can handle all these functionalities “at a smaller scale.”
Giving Durable Objects an open source home
Dahl is one of the world’s foremost experts at JavaScript I/O, having created Node.js, a JavaScript runtime that runs the world’s fastest Web applications (and inadvertently introduced the JavaScript world to “ callback hell,” where the language's asynchronous operations forced coders to pass functions as nested callbacks, resulting in ungainly and unintuitive messes of code). Dahl later went on to refine his ideas of asynchronous JavaScript with a second-generation JavaScript runtime called Deno.
Celld does away with the Cloudflare backend, and instead uses the Amazon Simple Storage Service (S3) or equivalent as the storage engine. It also uses the Tokio Rust asynchronous runtime. As with Durable Objects, each celld object gets its own copy of SQLite.
Dahl promises this open source backend will be “orders of magnitude cheaper at scale” than Durable Objects.
Dahl estimated that 100 resident Durable Object cells cost $415 a month on Cloudflare, whereas the celld implementation would run only about $49 a month, built on a DigitalOcean S3-compatible bucket on an 8 GB droplet. Further savings should ensue as the workload scales, he argued.
Cloudflare disputed Dahl’s numbers, stipulating that $415 a month would be the cost if all the objects were continuously active. If left to slumber, the Durable Objects would cost only $20.65 to house on Cloudflare, a spokesperson told The Register.
Whatever its putative thriftiness, the model itself seems to have gained interest on its own merits. “So happy to see support for running durable objects outside of one provider. Upvoted,” one Hacker News reader enthused, noting the concept of a durable object is a valuable abstraction.
MORE CONTEXT
Indeed, other parties are cooking their own schemes to move the data closer to the computation. For instance, Postgres service provider Neon just introduced its own Neon Functions, which can also co-locate data and compute for long-running workloads.
Written in Rust and JavaScript, celld is available under an Apache 2 license. It can ingest JavaScript and TypeScript code. In theory, Rust, C/C++, Go, or Zig code can also be executed through the magic of WebAssembly, which V8 supports with slight modification.
But while celld is open source, AI contributions are verboten. “Coding agents make it too easy to send a large, low-context change that costs maintainers more time than it saves,” the GitHub page notes. Human contributions are still welcome, though you should understand what your code does before you submit it. ®
