Are Web Apps inside an Azure App Service Plan implemented as virtual web servers in IIS? Are web gardens used?

Question

If Azure App Service plans are virtual machines dedicated to the Web, API, Logic, and Mobile apps defined within them, does that mean that a web app in an app service plan is an instance of a virtual web server in IIS on that virtual machine?

Assuming this is the case and that each virtual web site gets it's own application pool, is there an Azure scaling strategy or scenario where more than one worker process in that app pool will run, creating a web garden? My understanding of web app scale out is that it results in additional VMs being allocated and not additional worker processes.

Answer 1

The scaling strategy will depend upon the pricing tier you have opted for.

Basically each Service Plan will contain a collection of Web, API, Logic, Mobile apps. These will form a web garden within the Service Plan server you choose.

If you initially choose a single B1 Basic Service Plan, you will get a single virtual machine with all of your applications running on that. As the load on that server increases, you can scale it up to larger servers, but it will still be running on a single server.

If you then choose to create a second instance (and a 3rd, 4th, 5th...) that second server will be a replica of the first server, with the load being balanced between the two. (3,4...)

While I've not seen documentation for this, I would imagine that each Web, API, etc app is run under its own application pool / worker process, and scale out is simply duplicated instances.

Answer 2

I'm not sure what a Virtual Server is, but each app runs in its own dedicated application pool and w3wp.exe process. There is only a single w3wp.exe process per application pool, so no web gardens.

Is there a specific reason you think you need these to scale your apps? In most cases, using web gardens is the wrong way to scale, as adding more processes can cause unnecessary overhead (amongst other problems - you can find some useful resources on the web). You almost always want to prefer threads over processes for improving concurrency. If you're running out of physical resources (CPU, memory, etc), then the correct way to scale is to add additional VMs.