Introduction to Azure Functions

Azure Functions is Azure's event-driven, serverless compute service. It lets you run small pieces of code — called functions — without provisioning or managing servers. Each function is triggered by an event, executes its logic, and returns a result. This lesson covers the fundamentals: creating your first function, understanding the project structure, supported languages, and the development workflow.

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What is an Azure Function?

An Azure Function is a single unit of execution — a method or function in code — that runs in response to a trigger. Functions are:

• Stateless — each invocation is independent (unless using Durable Functions)
• Short-lived — designed to execute quickly and return
• Event-driven — always started by a trigger, never by polling or manual start
• Scalable — the platform can run thousands of instances simultaneously

A function app is the container that hosts one or more related functions. It provides the execution context, configuration, and deployment unit. All functions within a function app share the same configuration, connection strings, and pricing plan.

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Supported Languages and Runtimes

Azure Functions supports multiple languages across two programming models:

In-Process (Classic)

The function runs inside the Azure Functions host process:

Language	Runtime
C# (class library)	.NET 6/8

Isolated Worker / Out-of-Process

The function runs in a separate worker process, offering greater flexibility:

Language	Runtime
C# (isolated)	.NET 6/8/9
JavaScript/TypeScript	Node.js 18/20
Python	3.9/3.10/3.11
Java	8/11/17/21
PowerShell	7.2/7.4
Go, Rust, etc.	Custom handlers

Recommendation: For new C# projects, always use the isolated worker model. The in-process model is being phased out.

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Creating Your First Function

Prerequisites

Install the following tools:

• Azure Functions Core Tools (v4) — the local development runtime
• Azure CLI — for authentication and deployment
• Visual Studio Code with the Azure Functions extension (optional but recommended)

Using the CLI

# Install Azure Functions Core Tools (macOS)
brew tap azure/functions
brew install azure-functions-core-tools@4

# Create a new function app project
func init MyFunctionApp --worker-runtime javascript

# Navigate into the project
cd MyFunctionApp

# Create a new HTTP-triggered function
func new --name HelloWorld --template "HTTP trigger"

Project Structure

After initialisation, the project looks like this:

MyFunctionApp/
├── src/
│   └── functions/
│       └── HelloWorld.js       # Your function code
├── host.json                   # Global configuration for the function app
├── local.settings.json         # Local environment variables and connection strings
├── package.json                # Node.js dependencies
└── .funcignore                 # Files to exclude from deployment

The Function Code (JavaScript v4 Model)

const { app } = require('@azure/functions');

app.http('HelloWorld', {
    methods: ['GET', 'POST'],
    authLevel: 'anonymous',
    handler: async (request, context) => {
        context.log('HTTP trigger function processed a request.');

        const name = request.query.get('name')
            || (await request.text())
            || 'World';

        return { body: `Hello, \${name}!` };
    }
});