Does each Azure "App Service" instance run on its own VM?

Question

(Note that I'm using the new "blade" Azure Portal exclusively and use the new terminology, so avoid words like "Azure Website" as they do not apply here).

In the Portal I created two Azure App Services, "foo-production" and "foo-staging" - both exist in the same Subscription and Resource Group, and share the same App Service Plan. These App Services represent the production and staging deployments of a straightforward ASP.NET web application, which runs as a normal website.

The App Service Plan is "Basic: 1 Small".

My understanding is that when you use Azure App Services with a Basic or higher App Service Plan, that the Plan represents a VM which I'm able to host as many IIS websites as I want on - these IIS websites are represented in Azure as Azure App Services.

Given this, one would assume when I access the filesystem of the VM in Kudu ( https://yourwebsite.scm.azurewebsites.net/DebugConsole ) that I would be able to see each website's files under some common root directory.

However when I access the Kudu console for the foo-production website, I see that its files are in D:\home\site\wwwroot and files for foo-staging are not to be found.

If I'm understanding this correctly, it means that Azure actually created a whole new VM just for each website and that websites cannot share a filesystem - and that I cannot have a more advanced Azure-managed IIS configuration - I'd have to create my own self-managed Windows Server VM.

I can understand the motivation behind a separate VM for each website, it just seems wasteful - Windows Server requires at least a gigabyte of memory for each VM, yet my website is largely just static files (but I can't use a Shared App Service Plan because I need some of the more advanced functionality). That can't be economical for Microsoft then.

How can I have multiple Azure App Services in an Azure-managed environment share the same VM? Or am I thinking about it incorrectly?

To avoid an X/Y problem: I'll state that my primary concern is the persistence of files. The web-application I'm deploying stores uploaded files to a subdirectory of the webroot and those files should be there permanently. There is ambiguous information out there: some people suggest websites (and all their files) are actively destroyed and recycled and that Azure Storage Blobs should be used. I would like to use Azure File Shares, unfortunately I get ACCESS_DENIED errors when using WNetAddConnection2 and some users report that Azure File Shares cannot be used from within Azure App Services - though I cannot find anything authoritative from Microsoft about this.

Answer 1

If they are in the same App Service Plan, they are running in the same VM. Try typing hostname in Kudu Console for each and you'll see the same machine name.

But note that they each run in a different sandbox, which prevents them from seeing each other's files. Folders like d:\home are virtualized, and are actually pointing to network shares. So you can't use that to make conclusions as to the machines are the same.

Answer 2

As I answered here, all app services within a plan run in the same set of VMs, sharing all compute resources.

You assumed each app service within a plan shares files with all other app services. This is incorrect: Each app service will have its own set of files, in d:\home for each app service. If you need to share files, you'll need to use something external to App Services, like Azure File Service (an SMB share). Azure File Service is separate from the space created for you on a per-app-service basis.

Answer 3

1. An Azure "App Service" is analogous to a "Container" (Docker terminology). Although it's based on a VM, it's much lighter weight than a VM itself. For example, you cannot RDP into it.

2. An Azure "VM" is a full-fledged virtual machine. The OS can be Windows or any of several different flavors of Linux.

3. You can get more information here:

   • Azure App Service, Cloud Services, Virtual Machines, and Service Fabric comparison

Here is an excellent article that compares Web Sites (one example of an App Service), Cloud Services, and VMs:

http://www.c-sharpcorner.com/UploadFile/42ddd2/azure-websites-vs-cloud-service-vs-virtual-machines/

Azure Websites

Azure Websites has very little responsibility to complete, and relatively less control. It is the best choice for most web apps. Deployment and management are integrated directly into the platform we get.

Azure Cloud Services

If you want more, web server like environment you might want to go with Azure Cloud Services. You can remote into your cloud services and configure startup tasks. Cloud Services provide you more Ease of Management and Agility than Azure Websites

Azure Virtual Machines

Provides you rich set of features; however, correctly configuring, securing and maintaining VMs require much more time and more IT expertise compared to Azure Cloud Services and Azure Websites.