Do I need other roles than Worker Role for a web site and service layer in Azure?

Question

I've deployed web sites and services to the cloud before but it was a while ago and I wanted to revisit my approach to inventorize my skills. During the research, I've been told to use a worker role but I'm not sure in what constellation to apply it.

The image presents my choices. I'll be setting up two things (preferably on the same base URL).
1. A web site (ASP.NET, most likely MVC powered by Razor)
2. A service layer (guessingly WCF, as there's not much else to pick from today)

So, in my naive ignorance, I added ASP.NET Web Role for the former and WCF Service Web Role for the latter. Then, according to the hint, I also added Worker Role. And this is where I got humble and started to suspect that my ignorance was rather an arrogance...

Do I need all the three of them? Or is it perhaps so that Worker Role covers the others? Or are the others sufficient and I need to Worker Role? Or am I totally confusing the concepts here?

I've tried to google those but I realize that I haven't reached the threshold of learning by doing in this area yet. I get more confused and headacheish the more I read. Admittedly, my problem might lie in the wrong choice of search words and/or linguistic misconception. If so, my apologies...

Answer 1

The answer is, it depends...

A web role is essentially a Worker role with IIS installed + configured. You could host a WebApi/MVC, WCF AND process events all from the same web role if you really wanted to, reducing costs.

Remember that each role is a separate VM that you have to pay for, so adding extras roles to keep everything separate may not always be the best idea.

In one of our projects for example, we use a web role to host a WebApi. A Worker role to process internal events, and a worker role to host WCF services (you can also use a web role for this). We split them because they take very different workloads and perform separate functions, so being able to scale them independently made sense.

HTH

Answer 2

There's no right answer to how many roles to use in a cloud service. But it's important to understand exactly what those roles are.

Adding a bit to @Peter's answer: Each role is a definition of a VM (its contents) - think of it as a VM template. And for each role (template), you must have a minimum of one instance (VM) running. If you have one role, your minimum footprint will be one VM (of whichever size you specify for that role). If you have three roles, you'll have minimum 3 VMs running.

Whether you have one role or many depends on how you want to scale your application. Each role defines not only what goes in it, but also the size of the VMs uses by the role instances. By having different roles for different parts of your architecture, you can choose to scale those parts differently. For example, you might only need low-resource instances to handle your web tier, but maybe more CPU power for your service tier. And maybe your web tier scales dynamically based on user traffic, but you're able to handle, say, your service tier with just one or two instances. Of course, you can put everything in one role definition, and scale everything together. It's totally up to you.