Reactive Durable Functions

Durable Functions itself are a big topic and I'll come back to the them soon. In the previous post I

Durable Functions itself are a big topic and I'll come back to the them soon. In the previous post I created a simple Function App, which inserts a row into Table Storage. All activities were orchestrated and it was really easy to schedule more work. Today I want to present you how easy you can transform such active architecture into a passive one using Event Grid. This will be a fairly easy episode so let's start!

Function App

There's no need to change anything in the Function App since for now we'll use a HttpTrigger. Unfortunately we cannot host it locally(because of Event Grid) so there's a need to publish it to the cloud.

Event Grid

You can easily deploy Event Grid from the marketplace. For now there's nothing special regarding its installation, so I won't go into details.

Event Grid chosen from Marketplace - still in preview though

Combining it all together

Once we have components deployed we can configure Event Grid so it'll pass events to the chosen endpoint. In our case it'll be our Galaxy_Create_Start function(which we used to start orchestration). We'll need one thing - our function URL. To get it go to the Function App you deployed, find a function and click on Get Function URL.

Once you have it, we can go to Event Grid and create a new subscriber.

What we need now is a new subscription. This feature allow you to orchestrate events flow, so each subscriber can be subscribed to a particular event type. With this configured we can centralize the way, how e.g. multiple services built with Azure Functions integrate with event producers.

My subscriber configured and subscribed to nebula.galaxy event type

When you configure a new subscriber it will be added to the list of all supported subscribers. We've done all what we needed to integrate Event Grid with Azure Functions, let's test it now.

Working example

There're two important things what we need to test our solution - Event Grid endpoint and access key. The former ss available on the main screen - please copy it so you'll know where to post your messages. Access keys can be found under Settings section in Event Grid main menu.

Since we don't have any real producer yet, we'll try to simulate one. For this purposed I used Postman, however all is up to you. The only thing we have to do is to post a HTTP request to the mentioned enpoint. Here you have an example:

/
POST /api/events HTTP/1.1
Host: your.eventgrid.azure.net
aeg-sas-key: YOUR_KEY
Content-Type: application/json
Cache-Control: no-cache

[
    {
        "id": "2",
        "eventType": "nebula.galaxy",
        "subject": "nebula/galaxy/create",
        "eventTime": "2017-11-08T13:25:00+01:00",
        "data":{
        }
    }
]

As you can see the payload has a specific schema, which will be validated on the Event Grid side. In fact it should self-explanatory. What is important here is the fact, that this payload is being passed to the function. If you change the main function a little bit:

/
[FunctionName("Galaxy_Create_Start")]
public static async Task<HttpResponseMessage> StartOrchestration(
	[HttpTrigger(AuthorizationLevel.Function, "post", Route = "orchestration/start")] HttpRequestMessage req,
	[OrchestrationClient] DurableOrchestrationClient starter,
	TraceWriter log)
{
	// Function input comes from the request content.
	string instanceId = await starter.StartNewAsync("Galaxy_Create", null);

	var payload = await req.Content.ReadAsStringAsync();
	log.Info($"Started orchestration with ID = '{instanceId}'.");
	log.Info($"The payload is: {payload}");

	return starter.CreateCheckStatusResponse(req, instanceId);
}

You'll see following result when you go to the function and check the console:

/
2017-11-08T12:36:54.565 Function started (Id=ecb2655e-912e-435b-b916-f21b65729716)
2017-11-08T12:36:55.144 Started orchestration with ID = 'f7d2ad0001204ff0a381d61b448ef8b7'.
2017-11-08T12:36:55.144 The payload is: [{
  "id": "3",
  "eventType": "nebula.galaxy",
  "subject": "nebula/galaxy/create",
  "eventTime": "2017-11-08T12:25:00+00:00",
  "data": {},
  "topic": "/SUBSCRIPTIONS/____________/RESOURCEGROUPS/NEBULA-EUW-DEV-RG2/PROVIDERS/MICROSOFT.EVENTGRID/TOPICS/NEBULA-EUW-DEV-EVENTGRID"
}]
2017-11-08T12:36:55.173 Function completed (Success, Id=ecb2655e-912e-435b-b916-f21b65729716, Duration=596ms)

Of course you can easily deserialize it and incorporate into your flow.

Summary

As you can see implementing Event Grid as a gateway to the underlying architecture is a piece of cake. In fact we didn't need any change in our code - the whole integration perfomed seamlessly. In the next episode I'll try to present you how to integrate a producer(Event Hub), so we don't have to post messages directly to our Event Grid.

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