Do slots count as VMs in Azure?

Question

I currently have a web application deployed to Azure on the App Service free plan and, as part of going live, I'm interested in moving to the use of slots.

This is primarily because it gives me the ability to deploy new code into staging and then seamlessly swap over once it's been validated.

Now, to use slots, I know I need the standard plan and this clocks in at a minimum of $X per VM.

What I don't know (and frustratingly haven't been able to find out from the Azure stuff on Microsoft's web pages) is whether a second slot counts as another VM.

In one place at least, it states that deployment slots are live web applications with their own hostname but that could be read in at least two ways. either as a separate app on the same VM or a separate VM altogether.

Since the difference is substantial ($2X/month rather than $X/month), it's rather important to planning. So does anyone know how (preferably with some supporting citation from Microsoft) the slots are handled and charged for?

Answer 1

All deployed Azure sites in a given Web App plan run on the same VM instances. Just as if you deployed mysite1.azurewebsites.net and mysite2.azurewebsites.net in the same plan, they'd share the same VM instances. So, too, do extra deployment slots.

If you scale to 3 instances, you pay for 3 instances, and all deployments (all slots for all deployments) run on all three instances.

One way to make this easier to think about: the 'production' (or main) deployment slot is just another slot.