Serverless application with PowerShell: Azure Event Grid

This is part one of my blog series describing how you can create a serverless application infrastructure using PowerShell. The scope and history behind, covered in the introduction post. If you haven’t read that I recommend doing so.

Azure Event Grid

In my serverless infrastructure design, I have chosen to use Azure Event Grid as a hub for the other components in play. The other components will write and subscribe to events/messages in Event Grid and perform their given task as ‘their’ event arrives. Event grid fit’s the concept perfectly as you act on state changes. You can publish as many events you like, but you don’t need to subscribe to every one. A lot of Azures PaaS offerings are already fully integrated which makes it easy to get started.

Other event based offerings in Azure are Service Bus and Event Hub. You can read a little on the differences here

Set up Event Grid custom topic

I am sure you are able to create resources in Azure so here’s a quick one. Feel free to use what ever you want for deployment, but for the purpose of screenshots, I’m using the portal. Just remember that the name you chose will be the url of your endpoint as well.

After the custom topic is successfully deployed, you are given the option to subscribe to events. Before doing that we are taking a break. Besides a graph showing incoming events you have no good way to see your events as they arrive. This makes it way more difficult to debug why stuff isn’t working. While writing this post I researched for a good way to solve this and stumbled across this blog post by David Barkol. He created a web app that lets you view events as they arrive. You can deploy it directly from GitHub using ARM. Do this while your coffee is brewing. And come back here in 10 minutes 🙂

 

Subscribe to Event Grid topic

Welcome back… If you have deployed the web app you can follow and create a subscription subscribing to all events. In a production scenario, it’s likely to have scoped your subscribers, but in order for Event grid viewer to function i’ll subscribe to everything.

Once deployed your overview page will look something like this. Showing all subscriptions within your topic and their corresponding metrics. Now lets try to send a custom event using powershell.

Send event to event grid using PowerShell

Basically, event grid accepts post request to an API endpoint, which is the name of your topic plus a suffix and the API version. your full URI looks something like this; https://adatumblogdemo.northeurope-1.eventgrid.azure.net/api/events?api-version=2018-01-01

To authenticate we will pass an ‘aeg-sas-key’ within our request header. You will find the keys for authentication in the keys pane. Further event grid events has a schema you willl need to follow, meaning that all post requests will need to have some properties defined and your custom event data will be in a data property. The basics of it all looks like this

[
{
"topic": string,
"subject": string,
"id": string,
"eventType": string,
"eventTime": string,
"data":{
"custom": "data"
},
"dataVersion": string,
"metadataVersion": string
}
]

More details on the schema can be found on Msft Docs

If we combine everything we know this far, we can use the script below to post messages to event grid. Please add your own url and access key. Everything else should work.

Assuming no error messages, jump in to your event grid viewer to view the raw content like this;

A corresponding graph in the Azure portal could look something like this. Here you will see incoming events and how many matches your subscriptions in the same graph. You can also see individual metrics per subscription.

 

Summary

In this part of my blog series on how to create a serverless application infrastructure using PowerShell. We have walked through how to set up a custom Event Grid topic and how to post messages or event to it using standard PowerShell commandlets. We also deployed a custom web application capable of reading our incoming events in real time.

 

In the next part: For part two we are going to create an Azure Function running PowertShell that subscribes and send Event Grid messages. This is key to build up our infrastructure wich consists of multiple Azure Functions in order to work.