A few weeks ago Azure Event Grid service became available in preview. This service enables centralized management of events in a uniform way. It’s scales with you when the number of events increases. And this is made possible by the foundation the event grid relies on service fabric. Not only does is auto scale you also do not have to provision anything beside a Event Topic to support custom events (see my blog Routing an Event with a custom Event Topic). Event Grid is Serverless, you only pay for each action (Ingress events, Advanced matches, Delivery attempts, Management calls). Moreover, the price will be 30 cents per million action in preview, and will be 60 cents once the service will be GA.
Azure Event Grid can be described as an event broker that has one of more event publishers and subscribers. Event publishers are currently Azure blob storage, resource groups, subscriptions, event hubs and custom events. More will be added in the coming months like IoT Hub, Service Bus, and Azure Active Directory. Subsequently, there are consumers of events (subscribers) like Azure Functions, Logic Apps, and WebHooks. And more will be added on the subscriber side too with Azure Data Factory, Service Bus and Storage Queues for instance.
Azure Event Grid Storage registeration
Currently to capture Azure Blob Storage events you will need to register your subscription through a preview program. Once you have registered your subscription, which could take a day or two you can leverage Event Grid in Azure Blob Storage only in Central West US!
The Microsoft documentation on Event Grid has a section “Reacting to Blob storage events”, which contains a walkthrough to try out the Azure Blob Storage as an event publisher.
Azure Event Grid Storage Account Events Scenario
Having registered my subscription to the preview program I started exploring its capability as in the landing page of Event Grid sample scenario’s were explained. And I wanted to try out the serverless architecture sample, where one can use Event Grid to instantly trigger a serverless function to run image analysis each time a new photo is added to a blob storage container. Hence, I build a demo according to the diagram below.
An image will be uploaded to a Storage blob container, which will be the event source (publisher). Subsequently, the Storage blob container belongs to a Storage Account containing the Event Grid capability. And the Event Grid has three subscribers, a WebHook (Request Bin) to capture the output of the event, a Logic App to notify me a blob has been created and an Azure Function that will analyze the image created in the blob storage, by extracting the URL from the event and use it to analyze the actual image.
Intelligent routing
The screenshot below depicts the subscriptions on the events on the Blob Storage account. The WebHook will subscribe to each event, while the Logic App and Azure Function are only interested in the BlobCreated event, in a particular container(prefix filter) and type (suffix filter).
Besides being centrally managed Event Grid offers intelligent routing, which is the core feature of Event Grid. And you can use filters for event type, or subject pattern (pre- and suffix). Moreover, the filters are intended for the subscribers to indicate what type of event and/or subject they are interested in. When we look at our scenario the event subscription for Azure Functions is as follows.
- Event Type : Blob Created
- Prefix : /blobServices/default/containers/testcontainer/
- Suffix : .jpg
The prefix, a filter object, looks for the beginsWith in the subject field in the event. And the suffix looks for the subjectEndsWith in again the subject. In the event above you see that the subject has the specified Prefix and Suffix. See also Event Grid subscription schema in the documentation as it will explain the properties of the subscription schema. The subscription schema of the function is as follows:
The Azure Function is only interested in a Blob Created event with a particular subject and content type (image .jpg). And this will be apparent once you inspect the incoming event to the function.
The same intelligence applies for the Logic App that is interested in the same event. The WebHook subscribes to all the events and lacks any filters.
The scenario solution
The solution contains of a storage account (blob), registered subscription for Event Grid Azure Storage, Request Bin (WebHook), a Logic App and a Function App containing a function. The Logic App and Azure Function subscribe to BlobCreated event with the filter settings.
The Logic App subscribes to the event once the trigger action is defined. The definition is shown in the picture below.
Note that the resource name has to be specified explicitly (custom value) as the resource type Microsoft.Storage has be set explicitly too. The resource types that are listed are Resource Groups, Subscriptions, Event Grid Topics and Event Hub Namespace as Storage is still in a preview program. With this configuration the desired events can be evaluated and processed. In case of the Logic App it is parsing the event and sending an email notification.
Azure Function Storage Event processing
The Azure Function is interested in the same event. And as soon as the event is pushed to Event Grid once a blob has been created it will process the event. The url in the event https://teststorage666.blob.core.windows.net/testcontainer/NinoCrudele.jpg will be used to analyze the image. The image is a picture of my good friend Nino Crudele.
This image will be streamed from the function to the Cognitive Services Computer Vision API. The result of the analysis can be viewed in the monitor tab of the Azure Function.
The result of the analysis that Nino is smiling for the camera with confidence. The Logic App will parse the event and sent an email. The Request Bin will show the raw event. And in case I deleted the blob than this will only be captured by the WebHook (Request Bin) as it is interested in any event on the Storage account.
Summary
Azure Event Grid is unique in its kind as now other Cloud vendor has this type of service that can handle events in a uniform and serverless way. Although it is still early days as this service is in preview a few week. However, with expansion of event publishers and subscribers, management capabilities and other features it will mature in the next couple of months. The service is currently only available in the West Central US and West US, yet over course of time it will become available in every region. And once it will become GA the price will increase.
Working with Storage Account as source (publisher) of events unlocked new insights in the Event Grid mechanisms. Moreover, it shows the benefits of having a managed service by Azure for events. And the pub-sub and push of events are the key differentiators towards the other two services Service Bus and Event Hubs. No longer do you have to poll for events and/or develop a solution for it. To conclude the Service Bus Team has completed the picture for messaging and event handling.
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