Azure Functions Programming Model

This document outlines the core programming model of Azure Functions, explaining how to define, develop, and deploy serverless functions.

Core Concepts

Azure Functions is a serverless compute service that enables you to run code without provisioning or managing infrastructure. The programming model is designed to be flexible and extensible, allowing you to use your preferred language and development tools.

Triggers

Triggers define how a function is invoked. They are the events that cause your function to execute. Examples include HTTP requests, timer events, or messages arriving in a queue.

• Each function must have exactly one trigger.
• Triggers can have associated input and output bindings.

Bindings

Bindings simplify the process of connecting to other Azure services or external data sources. They allow you to declaratively specify how your function interacts with data, without writing boilerplate code for service integration.

• Input Bindings: Used to pass data from a service into your function.
• Output Bindings: Used to send data from your function to another service.

Function App

A Function App is the hosting environment for your individual Azure Functions. It allows you to group related functions together, manage their configuration, and deploy them as a single unit. A Function App shares the same hosting plan, runtime, and deployment settings.

Developing Your Functions

Supported Languages

Azure Functions supports a variety of programming languages, including:

• C#
• JavaScript
• TypeScript
• Python
• Java
• PowerShell
• F#

Local Development

You can develop and test Azure Functions locally using the Azure Functions Core Tools. This provides a local runtime environment that mimics the cloud execution environment.

Project Structure

A typical Azure Functions project has the following structure:

/YourFunctionApp
    host.json       // Global configuration for the Function App
    local.settings.json // Local environment variables and connection strings
    .gitignore
    /YourFunctionName
        function.json   // Function-specific configuration (triggers and bindings)
        index.js        // Or index.cs, __init__.py, etc. - your function code
    /AnotherFunctionName
        function.json
        run.csx         // Example for C# script

function.json

This file defines the triggers and bindings for a specific function. It's a JSON file that specifies the direction, type, and configuration of each binding.

{
  "scriptFile": "../run.csx", // For C# script, points to the code file
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}
            

host.json

This file contains global configuration options that affect all functions within a Function App, such as logging levels, HTTP settings, and extension configurations.

Deployment

You can deploy your Azure Functions to the cloud using various methods:

• Azure CLI
• Visual Studio Code with Azure Functions extension
• Visual Studio
• Azure DevOps
• GitHub Actions

Runtime and Execution

Azure Functions run on a configurable runtime. You can choose different runtime versions and operating systems (Windows or Linux).

Statelessness

By default, Azure Functions are stateless. Each execution of a function is independent of previous executions. For stateful workflows, consider using Azure Durable Functions.

Scalability

Azure Functions automatically scales your application based on demand. The Consumption plan provides automatic scaling, while other plans offer more control over scaling behavior.