In this example, we are going to route events from Event Grid to an Azure function. First, we need to create a new Event Grid Topic in Azure. To create this, follow these steps:

1. Navigate to the Azure portal by opening https://portal.azure.com.
2. Click Create a resource, type Event Grid Topic in the search bar, and create a new Event Grid Topic.
3. Add the following values:
   1. Name: PacktEventGridTopic.
   2. Subscription: Pick a subscription.
   3. Resource group: Create a new one and call it PacktEventGridResourceGroup.
   4. Location: East US.
   5. Event Schema: Event Grid Schema.
4. Click Create.
5. Next, we are going to create a new Azure function. 
6. Click Create a resource, type Function App in the search bar, and create a new function app.
7. Add the following values:
   1. Subscription: Pick a subscription.
   2. Resource group: Select PacktEventGridResourceGroup.
   3. Function App Name: PacktEventGridFunction.
   4. Publish: Code.
   5. Runtime Stack: .NET Core.
   6. Region: East US.
8. Click Review + create and then create.
9. When the function app is created, navigate to the settings and click on the function app:

10. Click the +, on the right-hand side of Functions. Then, select in-portal to create the function app in the Azure portal:

11. Click Continue.

12. Then, click More templates... and then Finish and view templates. In the next screen of the wizard, scroll down a bit and select Azure Event Grid trigger:

13. If you get a notification that Microsoft.Azure.WebJobs.Extensions.EventGrid is not installed, then install it.
14. Keep the default settings, and then click Create:

15. When the trigger is created, the run.csx file is opened by default. Click on the Add Event Grid subscription link in the top menu:

16. Add the following values:
    
    1. Name: PacktEventSubscription.
    2. Event Schema: Event Grid Schema.
    3. Topic Types: Event Grid Topics.
    4. Subscription: Pick a subscription.
    5. Resource group: Select PackEventGridResourceGroup.

1. 6. Resource: PacktEventGridTopic:

17. Click Create. This will create a new event subscription that subscribes to the
    Event Grid Topic.
18. Now, open PowerShell, and run the following commands. 
19. First, we need to log in to the Azure account:

Connect-AzAccount

20. If necessary, select the correct subscription:

Select-AzSubscription -SubscriptionId "********-****-****-****-***********"

21. Get a reference to the endpoint and the key:

$endpoint = (Get-AzEventGridTopic `
            -ResourceGroupName PacktEventGridResourceGroup `
            -Name PacktEventGridTopic).Endpoint

$keys = Get-AzEventGridTopicKey `
        -ResourceGroupName PacktEventGridResourceGroup `
        -Name PacktEventGridTopic

22. Create a random event ID and sort the date and time:

$eventID = Get-Random 99999
$eventDate = Get-Date -Format s

23. Construct the body using a hash table:

$htbody = @{
    id= $eventID
    eventType="recordInserted"
    subject="myapp/packtpub/books"
    eventTime= $eventDate
    data= @{
        title="Microsoft Azure Architect Technologies"
        eventtype="Ebook"
}
dataVersion="1.0"

24. Use ConvertTo-Json to convert the event body from the hash table to a JSON object. Append square brackets to the converted JSON payload, since they are expected in the event's JSON payload syntax:

$body = "["+(ConvertTo-Json $htbody)+"]"
Invoke-WebRequest -Uri $endpoint -Method POST -Body $body -Headers
@{"aeg-sas-key" = $keys.Key1}

25. This will create a custom event. You can now check the Azure Function logs for the result (the Azure Function logs have a delay of 5 minutes).

In this demonstration, we've routed an event from Azure Event Grid to an Azure function. In the next section, we are going to cover how to design an effective messaging architecture.