functions-event-grid-blob-trigger.md

title	description	author	ms.topic	ms.date	ms.author	ms.devlang
Azure Functions Event Grid Blob Trigger	Learn to setup and debug with the Event Grid Blob Trigger	cachai2	conceptual	3/1/2021	cachai	csharp, java, python

Azure Function Event Grid Blob Trigger

This article demonstrates how to debug and deploy a local Event Grid Blob triggered function that handles events raised by a storage account.

Note

The Event Grid Blob trigger is in preview.

Prerequisites

• Create or use an existing function app
• Create or use an existing storage account
• Have version 5.0+ of the Microsoft.Azure.WebJobs.Extensions.Storage extension installed
• Download ngrok to allow Azure to call your local function

Create a new function

1. Open your function app in Visual Studio Code.

2. Press F1 to create a new blob trigger function. Make sure to use the connection string for your storage account.

3. The default url for your event grid blob trigger is:

   C#

   http://localhost:7071/runtime/webhooks/blobs?functionName={functionname}

   Python

   http://localhost:7071/runtime/webhooks/blobs?functionName=Host.Functions.{functionname}

   Java

   http://localhost:7071/runtime/webhooks/blobs?functionName=Host.Functions.{functionname}

   ---

   Note your function app's name and that the trigger type is a blob trigger, which is indicated by blobs in the url. This will be needed when setting up endpoints later in the how to guide.

4. Once the function is created, add the Event Grid source parameter.

   C#

   Add Source = BlobTriggerSource.EventGrid to the function parameters.

   [FunctionName("BlobTriggerCSharp")]
   public static void Run([BlobTrigger("samples-workitems/{name}", Source = BlobTriggerSource.EventGrid, Connection = "connection")]Stream myBlob, string name, ILogger log)
   {
       log.LogInformation($"C# Blob trigger function Processed blob\n Name:{name} \n Size: {myBlob.Length} Bytes");
   }

   Python

   Add "source": "EventGrid" to the function.json binding data.

   {
     "scriptFile": "__init__.py",
     "bindings": [
       {
         "name": "myblob",
         "type": "blobTrigger",
         "direction": "in",
         "path": "samples-workitems/{name}",
         "source": "EventGrid",
         "connection": "MyStorageAccountConnectionString"
       }
     ]
   }

   Java

   Press F5 to build the function. Once the build is complete, add "source": "EventGrid" to the function.json binding data.

   {
     "scriptFile" : "../java-1.0-SNAPSHOT.jar",
     "entryPoint" : "com.function.{MyFunctionName}.run",
     "bindings" : [ {
       "type" : "blobTrigger",
       "direction" : "in",
       "name" : "content",
       "path" : "samples-workitems/{name}",
       "dataType" : "binary",
       "source": "EventGrid",
       "connection" : "MyStorageAccountConnectionString"
      } ]
   }

   ---

5. Set a breakpoint in your function on the line that handles logging.

6. Start a debugging session.

   C#

   Press F5 to start a debugging session.

   Python

   Press F5 to start a debugging session.

   Java

   Open a new terminal and run the below mvn command to start the debugging session.

   mvn azure-functions:run

   ---

[!INCLUDE functions-event-grid-local-dev]

Debug the function

Once the Blob Trigger recognizes a new file is uploaded to the storage container, the break point is hit in your local function.

Deployment

As you deploy the function app to Azure, update the webhook endpoint from your local endpoint to your deployed app endpoint. To update an endpoint, follow the steps in Add a storage event and use the below for the webhook URL in step 5. The <BLOB-EXTENSION-KEY> can be found in the App Keys section from the left menu of your Function App.

C#

https://<FUNCTION-APP-NAME>.azurewebsites.net/runtime/webhooks/blobs?functionName=<FUNCTION-NAME>&code=<BLOB-EXTENSION-KEY>

Python

https://<FUNCTION-APP-NAME>.azurewebsites.net/runtime/webhooks/blobs?functionName=Host.Functions.<FUNCTION-NAME>&code=<BLOB-EXTENSION-KEY>

Java

https://<FUNCTION-APP-NAME>.azurewebsites.net/runtime/webhooks/blobs?functionName=Host.Functions.<FUNCTION-NAME>&code=<BLOB-EXTENSION-KEY>

---

Clean up resources

To clean up the resources created in this article, delete the event grid subscription you created in this tutorial.

Next steps

• Automate resizing uploaded images using Event Grid
• Event Grid trigger for Azure Functions