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The event-subscription-with-dead-lettering project
event-grid-dotnet-handle-deadlettered-events

Azure Event Grid Dead Letter Samples for .NET

Contents

  1. The event-subscription-with-dead-lettering project
    • This project contains a sample that demonstrates how to create event subscriptions with dead-letter destinations and retry policies.
  2. The function-app project.
    • This project contains:
      • A function sample, WebhookSubscriptionFunction that acts as a web-hook subscription endpoint for the event subscription.
      • A function sample, ProcessDeadLetter that processes dead letter events.

Overview

This sample demonstrates:

  • How to create an event subscription with webhook destination, storage-blob dead letter destination and retry policy configuration
  • How to create a function that consumes dead letter events.

We will follow the following steps through this sample:

  1. Create an event grid event subscription with a webhook endpoint, dead letter destination and retry policies options.
    • Create a function which will serve as the web-hook endpoint for the event subscription. The WebhookSubscriptionFunction under the function-app handles the subscription handshake. It returns a 400 Bad Request to all other incoming requests. Note: the function is programmed in such a way to demonstrate the workings of dead letter destinations. A 400 Bad Request will cause the events to end up in the dead letter destination once they expire based on the retry policy.
    • Create an Azure Storage Blob Container which will be our dead letter destination for the event subscription.
  2. Demonstrate how to process dead letter events.
    • Create a function of type event grid trigger which will process dead letter events.

Prerequisites

  • .NET Core 2.0 or higher

Dependencies

  • Event Grid management plane SDK (Microsoft.Azure.Management.EventGrid).

Installation

  • Visual Studio 2017 Version 15.5 or later, with "Azure Development" workload enabled.
  • Azure Functions Extension in Visual Studio 2017.
  • Clone this repository onto your local machine. Compile the samples inside Visual Studio, the required Microsoft Azure Event Grid SDK components will automatically be downloaded from nuget.org.

Running the Sample

The following are the steps for running this sample end to end:

  1. Create an Event Grid topic:

    • Create an Event Grid topic first.
    • Follow steps for creating a topic here.
    • Make a note of the topic name and resource group name.

  2. Create a Storage Blob Container

    • Create an azure storage blob container as a destination for the dead letter events.
    • Follow steps for the same here.

  3. Creating Azure Functions:

    • Build the function-app in Visual Studio. Right click on the project in Visual Studio, and click Publish to publish the WebhookSubscriptionFunction and ProcessDeadLetterFunction to the cloud as an Azure Function. For more details, please refer to the steps described here.

    • Once this is published as an Azure function, navigate to the newly published WebhookSubscriptionFunction in Azure Portal. Click on "Get Function URL" button for the WebhookSubscriptionFunction and copy the function URL.

    • Navigate to the ProcessDeadLetter function in Azure Portal. Click on the "Add Event Grid subscription" option to create a new event subscription for this event grid trigger function. For the Create Event Subscription form, follow the below guidelines: Topic Type: Select Storage Accounts as the Topic Type Resource Group: use an existing Resource Group (same as the dead letter storage account in Step 3) Instance: Look for the storage account created in step 3 under the Instance dropdown SubscriberType: Webhook

      Alternately, use the below azure shell commands to create this event susbscription:

      #replace values within <> with appropriate settings
set azure_subscription_id=<azure_subscription_id>
set storage_account_name=<storage_account_name>
set resource_group_name=<resource_group_name>
set function_url=<endpoint> 
set event_subscription_name=<event_subscription_name>

#setting azure subscription id
az account set --subscription $azure_subscription_id  

storageid=$(az storage account show --name $storage_account_name --resource-group $resource_group_name --			query id --output tsv)
endpoint=$endpoint

#create event grid subscription 	
az eventgrid event-subscription create \
--resource-id $storageid \
--name $event_subscription_name \
--endpoint $endpoint

      Note: In the above commands, the <storage_account_name> and <resource_group_name> should be the same as the account created in step 2. The <function_url> refers to the Url for the ProcessDeadLetter function.

    • In this step we just created and deployed two functions under the function-app project. - WebhookSubscriptionFunction to serve as a webhook endpoint for the subscription we will create in the next step - ProcessDeadLetterFunction to process dead letter events

  4. Create an Event Subscription

    • Create an event subscription to the topic created in step 1 using the event-subscription-with-dead-lettering project.
    • Provide the WebhookEventSubscription Azure function URL from step 2. as a web-hook destination endpoint for the subscription.
    • Provide the Azure Storage Blob ResourceId and Container Name for the dead letter destination.
    • Select appropriate values for the retry policy configuration.
    • Replace all the values, build and run the project to create the event subscription.
    • Alternately, This shows how to create an event subscription using the CLI.

  5. Publish Events:

    • Use the Event Grid Publisher project to publish events.

  6. Verify Receipt of Events: In this step, we will be verifying that the events are delivered to the event subscription function. Here are the steps:

    • In the Logs view of the WebhookSubscriptionFunction, verify look through the logs that show the receipt of the EventGridEvent.
    • Since the function responds with a Bad Request to events, should start seeing those events appear in the dead letter destination.
    • Verify the receipt of events in the dead letter destination by looking at the blob files under the storage account through the portal.

  7. Process the Dead Letter Events:

    • Look at the Logs view for the ProcessDeadLetter function in the portal. The function should be triggered by the BlobCreated event whenever a new dead letter event is delivered to the blob container/dead letter destination.
    • Editing the ProcessDeadLetter function and republishing should allow the processing of dead letter events. Note: Look for The TODO comment in the ProcessDeadLetter function to add code to further process the dead letter events.

Resources

(Any additional resources or related projects)