Azure Durable Functions

Durable Functions is an extension of Azure Functions that enables you to write stateful functions in a serverless environment. They manage state, checkpoints, and restarts automatically, so you don’t have to manually store state or manage the infrastructure.

Key Features:

• Stateful Execution: Functions maintain their state throughout execution.
• Automatic Scaling: Functions scale as per demand.
• Reliable Workflows: Supports retries, parallel execution, and state persistence.
• Event-Driven Processing: Can respond to external events like user input, HTTP triggers, and messages from queues.

 Key Concepts:

• Orchestrator Function: Coordinates the workflow and calls other functions in a defined sequence.
• Activity Function: Performs the actual work (e.g., calling an API, doing calculations).
• Client Function: Triggers the orchestration (usually via HTTP request or queue).

Why Use Durable Functions?

• Chaining functions: Call multiple functions in sequence.
• Fan-out/fan-in: Run functions in parallel and wait for all to finish.
• Long-running workflows: Durable Functions can persist for days, weeks, or even longer.
• Timers and delays: Wait for a specific time before resuming.
• Human interaction: Pause the workflow and wait for external approval/input.

How to implement Azure Durable Functions?

Example of how to implement Azure Durable Functions in a Node.js project, demonstrating the three core components:

1️. Orchestrator Function (OrchestratorFunction/index.js)

Example:

java script
const df = require("durable-functions");

module.exports = df.orchestrator(async function (context) {
    const userId = context.df.getInput();

    const userInfo = await context.df.callActivity("getUserData", userId);

    return {
        user: userInfo
    };
});

Activity Functions

ActivityFunctions/getUserData.js

java script
module.exports = async function (context) {
    const userId = context.bindings.name;    
    return {
        id: userId,
        name: "John",
        activity: [20, 15, 20]
    };
};

Client Function (ClientFunction/index.js)

Java script
const df = require("durable-functions");
module.exports = async function (context, req) {
    const client = df.getClient(context);
    const userId = req.query.userId || (req.body && req.body.userId);
   const instanceId = await client.startNew("OrchestratorFunction",userId);
    return client.createCheckStatusResponse(context.bindingData.req, instanceId);
};

Azure Durable Functions are ideal for scenarios that require stateful, long-running workflows. They simplify the development of complex business processes, enhance scalability, and improve resilience while reducing the operational overhead associated with managing infrastructure and state. By leveraging these functions, you can build robust, efficient, and scalable applications with minimal management effort.