'Durable'

The term "durable" is gaining traction in the serverless world, signifying the ability to maintain state where it's not typically expected. A standard cloud function, for instance, operates as a clean slate each execution, lacking memory of past runs. However, a "durable" function, like a class instance with a unique ID, persists its state. This instance remains accessible as needed, retaining information across multiple invocations.

Cloudflare's Durable Objects exemplify this: they're JavaScript (or other language) class instances with globally unique IDs. Each object's persistent state is private and stored on disk, allowing for fast access. Even though the in-memory object is shut down when idle, it's recreated on demand. This enables compelling real-time applications.

Azure's Durable Functions, specifically Entity Functions, offer a similar concept. These act as miniature services communicating via messages, each with a unique ID and internal state (if applicable). Operations update the internal state and can interact with external services. Communication occurs through reliable queues, facilitating real-time scenarios like displaying a game's score to connected players. While the documentation might be more complex, the underlying principle mirrors Cloudflare's approach: persistent, identifiable objects for real-time applications.

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