Azure Functions Documentation

Introduction to Developing Azure Functions

Azure Functions is a serverless compute service that lets you run code on demand without explicitly provisioning or managing infrastructure. With Azure Functions, you can build applications by connecting to other services, automating processes, and building APIs.

This document provides a comprehensive guide to developing Azure Functions, covering supported languages, development environments, triggers, bindings, local development, testing, and best practices.

Supported Languages

Azure Functions supports a variety of popular programming languages, allowing you to develop using the tools and ecosystems you're familiar with. The primary supported languages include:

• C# (.NET)
• JavaScript (Node.js)
• TypeScript
• Python
• Java
• PowerShell
• Go (Preview)

Each language has specific runtime requirements and development patterns. Refer to the language-specific documentation for detailed guidance.

Development Environments

You can develop Azure Functions using several integrated development environments (IDEs) and command-line tools:

Visual Studio Code

Visual Studio Code (VS Code) is a popular, lightweight, and free code editor with excellent support for Azure Functions through the Azure Functions extension. It provides a rich debugging experience, integrated tooling, and project management capabilities.

Key Features:

• IntelliSense and code completion
• Debugging capabilities for all supported languages
• Easy creation and management of Functions projects
• Deployment integration with Azure

Visual Studio

For .NET developers, Visual Studio offers a robust and integrated experience for developing Azure Functions. It provides comprehensive tooling for C# development, including project templates, debugging, and deployment.

Key Features:

• Project templates for various Function types
• Powerful debugger
• Seamless integration with Azure services

Azure Functions Core Tools

Azure Functions Core Tools is a command-line interface (CLI) that allows you to develop, test, and deploy Azure Functions locally. It's essential for scripting, automation, and for developers who prefer a command-line workflow.

Key Features:

• Create new Function projects and functions
• Run and debug functions locally
• Local emulation of Azure Functions runtime
• Deployment to Azure

You can install Core Tools via npm:

npm install -g azure-functions-core-tools@4 --unsafe-perm true

Function Triggers

A trigger defines how a function is invoked. Each Azure Function must have exactly one trigger. Triggers can be based on events from Azure services or external sources. Common triggers include:

• HTTP Trigger: Invokes a function in response to an HTTP request.
• Timer Trigger: Invokes a function on a schedule.
• Blob Trigger: Invokes a function when a new or updated blob is detected in Azure Blob Storage.
• Queue Trigger: Invokes a function when a message is added to an Azure Storage Queue.
• Event Hub Trigger: Invokes a function in response to events from an Event Hub.
• Service Bus Trigger: Invokes a function when a message is received from an Azure Service Bus queue or topic.

The trigger configuration is typically defined in a function.json file (for Node.js, Python, PowerShell, and Java) or through attributes (for C#).

Function Bindings

Bindings are a declarative way to connect your function to other Azure services and external data sources, without requiring you to write plumbing code. They simplify interaction with services like storage, databases, and messaging queues.

Bindings are categorized into two types:

• Input Bindings: Provide data to your function.
• Output Bindings: Send data from your function to another service.

Example: A Blob Storage input binding can automatically download a file into your function's parameters, and a Cosmos DB output binding can write data to a document without explicit SDK calls.

Local Development

Developing and testing your Azure Functions locally before deploying to the cloud is crucial. Azure Functions Core Tools provides a local runtime environment that mimics the Azure Functions host.

Steps for Local Development:

1. Install Azure Functions Core Tools.
2. Create a new Functions project using the CLI or your IDE.
3. Add functions with desired triggers and bindings.
4. Run the local host using the command:

func start

5. Test your functions via HTTP requests or by triggering the relevant services.

Testing Functions

Effective testing ensures the reliability and correctness of your Azure Functions.

Types of Testing:

• Unit Testing: Test individual functions in isolation. You can mock dependencies and trigger inputs.
• Integration Testing: Test interactions between your function and other services (e.g., a blob trigger with actual blob storage).
• End-to-End Testing: Test the complete flow of your application, from trigger to output.

Use your language's standard testing frameworks (e.g., MSTest, xUnit for C#; Jest, Mocha for JavaScript; Pytest for Python) to implement these tests.

Best Practices for Development

• Choose the Right Trigger and Bindings: Select triggers and bindings that best match your event-driven scenario.
• Keep Functions Small and Focused: Each function should perform a single, well-defined task.
• Manage Dependencies Effectively: Use package managers and consider dependency injection.
• Handle Errors Gracefully: Implement robust error handling and logging.
• Optimize for Cold Starts: For stateless functions, consider how to minimize startup time.
• Secure Your Functions: Use appropriate authentication and authorization, especially for HTTP-triggered functions.
• Monitor Performance: Utilize Application Insights for detailed monitoring and diagnostics.