Azure Event Grid is one of the newest products available in Azure cloud stack. Since it's still in preview, we are not offered full functionality(so e.g. only two regions can be selected, not all event publishers have been added). However with all the goodnes provided by this component, we can start thinking about "reactive programming in the cloud" - at least this is what documentation tells us. Let's dive deeper into Event Grid and find why it's so special.
Event Grid is all about events. You may ask how it is different comparing similar products like Event Hub or Service Bus. If you take a look at the basic architecture, you'll find very similar concept like topics or subscribers (well at least for Service Bus). So why do I need Event Grid(which will complicate my architecture even more) when I can easily connect e.g. my Azure Functions to a topic and achieve the same functionality with ease? Well, this is only partially true.
Event Grid functional model(source: https://docs.microsoft.com/en-us/azure/event-grid/overview)
The downside of other solutions is the need of pooling - details doesn't matter now, you have to implement some way of communication between your app and an event publisher. It can be long-pooling, event sourcing, WebSockets - whatever works can be used. So even if you establish a persistent connection, you have to talk to the other side and await messages. You're not passive in this model - that's why you cannot "react" on events passed to you. You only parse them and pass further.
Event Grid allows you to make your components "passive" - they are somewhere in the cloud and are only interested in the data you send to them. They don't have to persist any connections - it's up to Event Grid to distribute messages and deliver to the configured subscribers. Microsoft states, that this approach is suited for serverless scenario and I can agree with them - you can make underlying infrastructure even more abstract and control the flow of event from the single point. For me the possibility to configure connection between Event Hub and several Azure Functions using Azure Portal(so I don't have to pass a connection string of EH to each individual component) is definitely a big YES to Event Grid.
Should I go for it?
I still think, that though Event Grid simplifies and improves working with serverless architecture(what am I saying - it actually enables you to start thinking about serverless at all...), you cannot just take it, write a couple of Functions and say "this is how we're making applications today in our company". It still requires proper planning, it's still not valid for each and every application(with Event Hub, Event Grid and Azure Functions, you may assume, that an event will reach its destination... at some point in time) and forces you to change your mindset into being "reactive"(and this is sometimes a challenge itself).
Event Grid as the "man-in-the-middle" in serverless architecture(source: https://docs.microsoft.com/en-us/azure/event-grid/overview)
On the other hand I like how it smoothly integrates with the cloud - for now only a few publishers are available, but we're given a promise, that this will change soon. I treat it as a serverless orchestrator - it's the centre of my architecture, where I can separate concerns seamlessly. Combine it with negligible cost($0.60 per million operations, first 100k is free) and easy learning curve and ask yourself why haven't you tested it yet?