Running Azure Functions Locally

Running your Azure Functions locally is a crucial part of the development workflow. It allows you to test your functions and their dependencies without deploying to Azure, significantly speeding up the development cycle and enabling effective debugging.

Introduction

The Azure Functions runtime provides a local development experience that mimics the Azure Functions host environment. This enables you to develop, run, and debug your functions on your local machine before deploying them to the cloud.

The core tool for this local development experience is the Azure Functions Core Tools. This command-line interface (CLI) allows you to create, build, and run function projects locally.

Prerequisites

Before you begin running your functions locally, ensure you have the following installed:

• Azure Functions Core Tools: See the next section for installation instructions.
• A supported programming language: Such as Node.js, Python, .NET, or Java.
• An Integrated Development Environment (IDE) or text editor: Such as Visual Studio Code, Visual Studio, or your preferred editor.

Install Azure Functions Core Tools

The recommended way to install Azure Functions Core Tools is via npm (Node Package Manager), which comes with Node.js. If you don't have Node.js installed, download it from nodejs.org.

To install or update the Core Tools globally, run the following command in your terminal:

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

For other installation methods (like Homebrew on macOS or Chocolatey on Windows), please refer to the official documentation.

Create a new project

You can create a new Azure Functions project using the Core Tools. Navigate to the directory where you want to create your project and run:

func init MyFunctionProj --worker-runtime 

Replace <language> with your chosen runtime (e.g., dotnet, node, python, java).

After initializing the project, you can add new functions using:

cd MyFunctionProj
func new --template "HTTP trigger" --name MyHttpTrigger

Run functions locally

Once your project is set up, you can start the local Functions host from your project directory:

func start

This command will build your project (if necessary) and start a local runtime that listens for requests. The output will show the endpoints for your triggered functions.

For HTTP-triggered functions, you'll see URLs like:

Http Functions:
                MyHttpTrigger: [GET,POST] http://localhost:7071/api/MyHttpTrigger

You can then use tools like curl, Postman, or your browser to send requests to these local endpoints.

Debug locally

Debugging locally is essential for troubleshooting. The process varies slightly depending on your programming language and IDE.

• Visual Studio Code:
  • Ensure you have the Azure Functions extension installed.
  • Open your project folder in VS Code.
  • Create a launch.json file if one doesn't exist (usually done through the extension or by running func start and then clicking the debug icon).
  • Select the appropriate debug configuration (e.g., "Attach to Node Functions", "Attach to .NET Functions").
  • Set breakpoints in your function code.
  • Press F5 (or click the debug button) to start debugging.
• Visual Studio:
  • Open your Azure Functions project.
  • Set breakpoints in your code.
  • Press F5 or click the Start button to debug. Visual Studio integrates with the Azure Functions Core Tools for a seamless debugging experience.
• Other IDEs/Languages:

  Generally, you will need to start the Azure Functions host in a separate terminal using func start, and then attach your IDE's debugger to the running process. Consult your IDE's documentation for specific attachment instructions.

Next steps

Once you're comfortable running and debugging your functions locally, you're ready to explore:

• Deploying your functions to Azure.
• Integrating with other Azure services.
• Implementing advanced features like Durable Functions.

Continue your learning journey with Deploying Functions with VS Code.