Welcome to Azure Functions Documentation

What are Azure Functions?

Azure Functions is a serverless compute service that lets you run event-driven code without explicitly provisioning or managing infrastructure. It's a powerful way to build and scale applications where individual components are triggered by various events. You pay only for the time your code runs, and scale automatically based on demand.

Core Concepts

• Functions: A unit of code that responds to an event.
• Triggers: What causes a function to run (e.g., HTTP request, timer, message queue).
• Bindings: Declarative ways to connect to other Azure services and data sources, simplifying input and output operations.
• Runtime: The environment where your functions execute.
• Consumption Plan: A pay-as-you-go plan where you are billed per execution and resource consumption.
• Premium Plan: Offers pre-warmed instances for faster cold starts and VNet connectivity.
• App Service Plan: Run Functions on dedicated VMs, similar to other App Service apps.

Getting Started

The fastest way to get started with Azure Functions is by using the Azure portal or the Azure CLI.

Using the Azure Portal

1. Navigate to the Azure portal.
2. Search for "Functions" and select "Function App".
3. Click "Create" and configure your Function App settings (subscription, resource group, name, runtime stack, region).
4. Once created, navigate to your Function App and click "Functions" > "Create" to add your first function.

Using Azure CLI

Install the Azure CLI and the Functions Core Tools. Then, create a new project:

func init MyFunctionProject --worker-runtime node
cd MyFunctionProject
func new --name MyHttpTrigger --template "HTTP trigger" --authlevel anonymous

You can then run your function locally:

func start

Developing Functions

Azure Functions supports various programming languages, including:

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

Function Structure

A function typically consists of a code file (e.g., index.js) and a configuration file (function.json) that defines its triggers and bindings.

Example function.json for an HTTP trigger:

{
  "scriptFile": "index.js",
  "bindings": [
    {
      "authLevel": "anonymous",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

Example index.js for the above trigger:

module.exports = async function (context, req) {
    context.log('JavaScript HTTP trigger function processed a request.');
    const name = (req.query.name || (req.body && req.body.name));
    const responseMessage = name
        ? 'Hello, ' + name + '!'
        : 'This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response.';

    context.res = {
        body: responseMessage
    };
};

Triggers and Bindings

Triggers and bindings are the heart of Azure Functions, allowing seamless integration with other services without writing boilerplate code.

Common Triggers:

• HTTP Trigger: Invoked via an HTTP request.
• Timer Trigger: Runs on a schedule (e.g., every 5 minutes).
• Blob Trigger: Fires when a new or updated blob is detected in Azure Blob Storage.
• Queue Trigger: Executes when a new message arrives in an Azure Storage Queue.
• Event Hub Trigger: Processes messages from an Azure Event Hub.
• Cosmos DB Trigger: Reacts to changes in a Cosmos DB collection.

Common Bindings:

• Output Bindings: Send data to services like Azure Table Storage, Cosmos DB, or send a notification via Twilio.
• Input Bindings: Read data from services like Azure Blob Storage or Event Grid.

Managing Functions

You can manage your Function Apps through the Azure portal, Azure CLI, or REST API.

• Deployment: Deploy code via Git, Zip Deploy, CI/CD pipelines (Azure DevOps, GitHub Actions).
• Configuration: Manage application settings, connection strings, and environment variables.
• Scaling: Functions automatically scale based on demand (Consumption plan) or can be configured for manual or auto-scaling (Premium/App Service plans).

Monitoring

Monitor your functions' performance and troubleshoot issues using:

• Azure Monitor: Provides metrics, logs, and alerts.
• Application Insights: Deep performance monitoring, live metrics, and end-to-end transaction tracing.
• Log Streaming: View real-time logs directly in the Azure portal.

Key metrics to watch include execution count, error count, function execution time, and memory usage.

Best Practices

• Keep functions small and focused: Each function should do one thing well.
• Manage dependencies: Use package managers (npm, pip, NuGet) effectively.
• Handle state externally: Use services like Azure Storage or Cosmos DB for persistent state.
• Optimize for cold starts: Choose appropriate language runtimes and consider the Premium plan if cold starts are critical.
• Secure your functions: Use authentication and authorization mechanisms.
• Implement robust error handling and logging: Make debugging easier.