Persisting State in Node-RED: Making Your Automations More Reliable

Node-RED is a powerful and user-friendly flow-based programming tool that enables rapid prototyping and automation development. Its intuitive visual interface and extensive library of pre-built nodes make it a popular choice for hobbyists and developers looking to create small-scale projects quickly. In this article, we'll explore different approaches to persisting state in Node-RED, with a focus on using the built-in contextStorage setting.

Node-RED provides an in-memory storage mechanism called "context" that allows you to persist data within a flow or globally across all flows. The context can store variables, objects, or any other data needed for your automation.

Flow Context: The flow context allows you to store data specific to a particular flow. This context is accessible to all nodes within the same flow and is ideal for storing flow-specific information.

Global Context: The global context stores data that is accessible across all flows. It acts as a shared storage for multiple flows and can be useful when you need to maintain state information throughout your entire Node-RED instance.

To use context, you can utilize the "context" object available within function nodes or the context-aware nodes provided by Node-RED. For instance, to set a value in flow context, you can use flow.set('key', value) and to retrieve it, use flow.get('key').

By default, Node-RED's context is stored in memory only, which means that its contents are cleared whenever Node-RED restarts. However, starting from the 0.19 release, Node-RED introduced a new configuration option called "contextStorage," which allows you to save context data for persistence across restarts.

With contextStorage, you can choose from different storage options, including local file system, a remote database, or custom storage mechanisms. The local file system storage is particularly convenient for small-scale projects. To enable context persistence via the local file system, add the following line to your Node-RED settings.js file:

contextStorage: {
    default: {
        module: "localfilesystem"
    }
}

Once enabled, Node-RED will automatically save the context to files, ensuring that the data is available even after restarts.

Node-RED's simplicity and efficiency make it a preferred choice for rapid automation development. While it may not be initially designed for production-ready systems, it provides an excellent platform for building small pet projects or proof-of-concept prototypes. By utilizing the built-in contextStorage feature and persisting state in files, Node-RED becomes even more reliable, ensuring that your automations continue functioning seamlessly, even after restarts.