Quickstart: Respond to blob storage events by using Azure Functions

In this quickstart, you use Visual Studio Code to build an app that responds to events in a Blob Storage container. After testing the code locally by using an emulator, you deploy it to a new serverless function app running in a Flex Consumption plan in Azure Functions.

The project uses the Azure Developer CLI (azd) extension with Visual Studio Code to simplify initializing and verifying your project code locally, as well as deploying your code to Azure. This deployment follows current best practices for secure and scalable Azure Functions deployments.

This article supports version 4 of the Node.js programming model for Azure Functions.

This article supports version 2 of the Python programming model for Azure Functions.

Prerequisites

An Azure account with an active subscription. Create an account.
Visual Studio Code on one of the supported platforms.
The Azure Functions extension for Visual Studio Code. This extension requires Azure Functions Core Tools. When this tool isn't available locally, the extension tries to install it by using a package-based installer. You can also install or update the Core Tools package by running Azure Functions: Install or Update Azure Functions Core Tools from the command palette. If you don't have npm or Homebrew installed on your local computer, you must instead manually install or update Core Tools.

.NET 8.0 SDK
C# extension for Visual Studio Code.

The Java Development Kit, version 8, 11, 17 or 21 (Linux).
Apache Maven, version 3.0 or above.
The Java extension pack

Node.js 18.x or above. Use the node --version command to check your version.

Python versions that are supported by Azure Functions. For more information, see How to install Python.
The Python extension for Visual Studio Code.

The Azure Developer CLI extension for Visual Studio Code.

Azure Storage extension
REST Client extension or an equivalent REST tool used to securely execute HTTP requests.

Initialize the project

Use the azd init command from the command palette to create a local Azure Functions code project from a template.

In Visual Studio Code, open a folder or workspace where you want to create your project.
Press F1 to open the command palette, search for and run the command Azure Developer CLI (azd): Initialize App (init), then choose Select a template.

There might be a slight delay while azd initializes the current folder or workspace.

When prompted, choose Select a template, then search for and select Azure Functions C# Event Grid Blob Trigger using Azure Developer CLI.
When prompted in the terminal, enter a unique environment name, such as blobevents-dotnet.

This command pulls the project files from the template repository and initializes the project in the current folder or workspace.

When prompted, choose Select a template, then search for and select Azure Functions Python Event Grid Blob Trigger using Azure Developer CLI.
When prompted in the terminal, enter a unique environment name, such as blobevents-python.

This command pulls the project files from the template repository and initializes the project in the current folder or workspace.

When prompted, choose Select a template, then search for and select Azure Functions TypeScript Event Grid Blob Trigger using Azure Developer CLI.
When prompted, enter a unique environment name, such as blobevents-typescript.

This command pulls the project files from the template repository and initializes the project in the current folder or workspace.

When prompted, choose Select a template, then search for and select Azure Functions Java Event Grid Blob Trigger using Azure Developer CLI.
When prompted, enter a unique environment name, such as blobevents-java.

This command pulls the project files from the template repository and initializes the project in the current folder or workspace.

When prompted, choose Select a template, then search for and select Azure Functions PowerShell Event Grid Blob Trigger using Azure Developer CLI.
When prompted, enter a unique environment name, such as blobevents-powershell.

This command pulls the project files from the template repository and initializes the project in the current folder or workspace.

In azd, the environment maintains a unique deployment context for your app, and you can define more than one. It's also part of the name of the resource group you create in Azure.

Set up local storage emulator

Use the Azurite emulator to run your code project locally before creating and using Azure resources.

If you haven't already, install Azurite.
Press F1. In the command palette, search for and run the command Azurite: Start to start the local storage emulator.
In the Azure area, expand Workspace > Attached Storage Accounts > Local Emulator, right-click (Ctrl-click on Mac) Blob Containers, select Create Blob Container..., and create these two blob storage containers in the local emulator:
- unprocessed-pdf: container that the trigger monitors for storage events.
- processed-pdf: container where the function sends processed blobs as output.
Expand Blob Containers, right-click (Ctrl-click on Mac) unprocessed-pdf, select Upload Files..., press Enter to accept the root directory, and upload the PDF files from the data project folder.

When running locally, you can use REST to trigger the function by simulating the function receiving a message from an event subscription.

Run the function locally

Visual Studio Code integrates with Azure Functions Core tools to let you run this project on your local development computer by using the Azurite emulator. The PDFProcessorSTORAGE environment variable defines the storage account connection, which is also set to "UseDevelopmentStorage=true" in the local.settings.json file when running locally.

Run this command from the src project folder in a terminal or command prompt:
```
func start
```
```
mvn clean package
mvn azure-functions:run
```
```
npm install
func start  
```
```
npm install
npm start  
```
When the Functions host starts, it writes the name of the trigger and the trigger type to the terminal output. In Functions, the project root folder contains the host.json file.
With Core Tools still running in Terminal, open the test.http file in your project and select Send Request to trigger the ProcessBlobUpload function by sending a test blob event to the blob event webhook.

This step simulates receiving an event from an event subscription when running locally, and you should see the request and processed file information written in the logs. If you aren't using REST Client, you must use another secure REST tool to call the endpoint with the payload in test.http.
In the Workspace area for the blob container, expand processed-pdf and verify that the function processed the PDF file and copied it with a processed- prefix.
When you're done, press Ctrl+C in the terminal window to stop the func.exe host process.

Review the code (optional)

You can review the code that defines the Event Grid blob trigger in the ProcessBlobUpload.cs project file. The function demonstrates how to:

Use BlobTrigger with Source = BlobTriggerSource.EventGrid for near real-time processing
Bind to BlobClient for the source blob and BlobContainerClient for the destination
Process blob content and copy it to another container by using streams

You can review the code that defines the Event Grid blob trigger in the function_app.py project file. The function demonstrates how to:

Use @app.blob_trigger with source="EventGrid" for near real-time processing
Access blob content using the InputStream parameter
Copy processed files to the destination container using the Azure Storage SDK

You can review the code that defines the Event Grid blob trigger in the processBlobUpload.ts project file. The function demonstrates how to:

Use app.storageBlob() with source: 'EventGrid' for near real-time processing
Access blob content using the Node.js Azure Storage SDK
Process and copy files to the destination container asynchronously

You can review the code that defines the Event Grid blob trigger in the ProcessBlobUpload.java project file. The function demonstrates how to:

Use @BlobTrigger with source = "EventGrid" for near real-time processing
Access blob content using BlobInputStream parameter
Copy processed files to the destination container using Azure Storage SDK for Java

You can review the code that defines the Event Grid blob trigger in the ProcessBlobUpload/run.ps1 project file and the corresponding function.json. The function demonstrates how to:

Configure blob trigger with "source": "EventGrid" in function.json for near real-time processing
Access blob content using PowerShell Azure Storage cmdlets
Process and copy files to the destination container using Azure PowerShell modules

After you review and verify your function code locally, it's time to publish the project to Azure.

Create Azure resources and deploy

Use the azd up command to create the function app in a Flex Consumption plan along with other required Azure resources, including the event subscription. After the infrastructure is ready, azd also deploys your project code to the new function app in Azure.

In Visual Studio Code, press F1 to open the command palette. Search for and run the command Azure Developer CLI (azd): Sign In with Azure Developer CLI, then sign in by using your Azure account.
In the project root, press F1 to open the command palette. Search for and run the command Azure Developer CLI (azd): Provision and Deploy (up) to create the required Azure resources and deploy your code.

When prompted in the Terminal window, provide these required deployment parameters:

Prompt	Description
Select an Azure Subscription to use	Choose the subscription in which you want to create your resources.
Environment name	An environment that's used to maintain a unique deployment context for your app.
Azure location	Azure region in which to create the resource group that contains the new Azure resources. Only regions that currently support the Flex Consumption plan are shown.

The azd up command uses your responses to these prompts with the Bicep configuration files to create and configure these required Azure resources, following the latest best practices:

Flex Consumption plan and function app
Azure Storage account with blob containers
Application Insights (recommended)
Access policies and roles for your account
Event Grid subscription for blob events
Service-to-service connections by using managed identities (instead of stored connection strings)

After the command completes successfully, your app runs in Azure with an event subscription configured to trigger your function when blobs are added to the unprocessed-pdf container.

Make a note of the AZURE_STORAGE_ACCOUNT_NAME and AZURE_FUNCTION_APP_NAME in the output. These names are unique for your storage account and function app in Azure, respectively.

Verify the deployed function

In Visual Studio Code, press F1. In the command palette, search for and run the command Azure Storage: Upload Files.... Accept the root directory, and as before, upload one or more PDF files from the data project folder.
When prompted, select the name of your new storage account (from AZURE_STORAGE_ACCOUNT_NAME). Select Blob Containers > unprocessed-pdf.
Press F1. In the command palette, search for and run the command Azure Storage: Open in Explorer. Select the same storage account > Blob Containers > processed-pdf, and then Open in new window.
In the Explorer, verify that the PDF files you uploaded were processed by your function. The output is written to the processed-pdf container with a processed- prefix.

The Event Grid blob trigger processes files within seconds of upload. This speed demonstrates the near real-time capabilities of this approach compared to traditional polling-based blob triggers.

Redeploy your code

Run the azd up command as many times as you need to both provision your Azure resources and deploy code updates to your function app.

Note

Deployed code files are always overwritten by the latest deployment package.

Your initial responses to azd prompts and any environment variables generated by azd are stored locally in your named environment. Use the azd env get-values command to review all of the variables in your environment that were used when creating Azure resources.

Clean up resources

When you're done working with your function app and related resources, use this command to delete the function app and its related resources from Azure. This action helps you avoid incurring any further costs:

azd down --no-prompt