UPDATE: For Azure Resource Manager virtual machine snapshots using managed disks read this post and for unmanaged disks read this post.
This post covers Azure Service Manager (ASM) virtual machines.
If you are familiar with VMWare and Hyper-V you’ll know how easy and handy it is to snapshot a VM and return to that snapshot later on. I use it especially when testing installers and automated deployments where you have to run them multiple times on a clean machine.
In this post I’m going to show you how to “snapshot” a VM in Azure and then revert back to that snapshot. I refer to it as a snaphot but Azure doesn’t support snapshots, this is more a workaround that involves capturing the VM virtual hard disk image and storing it in BLOB storage.
In other virtualisation platforms a snapshot captures the disk at that point in time, when you make changes to the file system in your VM your changes are written to a delta file that contains only the modifications from the previous snapshot. This way you can quickly revert back or roll forward between snapshots. This is a very simplified explanation, there is lots more if you want to read. In Azure it is not so quick since the whole VM image is captured and then restored when you revert back to it.
Something else I want to point out before we get started is the difference between generalised and specialised VM images. You can read the whole explanation here. In short you should not clone new VMs from a specialised image since it can lead to problems if your VM is in a domain. It also causes problems with other software like Octopus Deploy since every machine gets a unique certificate when the Tentacle is configured. If you are capturing a VM image to clone it, run SysPrep first to generalise it.
Now on to the fun part, the script. If this is your first time running PowerShell against Azure refer to this post to setup your environment. In PowerShell run the following to capture your image.
Save-AzureVMImage -ServiceName "YourServiceName" -Name "YourVmName" -ImageName "DescriptiveImageName" -OSState Specialized
If you open up the Cloud Explorer in Visual Studio you will see your new VHD image under:
Storage Accounts -> YourStorageAccountName -> Blob Containers -> vhds
Or you can see it in the portal under your storage account.
To revert back to this image you have to delete your existing VM and its disk and create a new one from this saved VHD image. First make sure your image was created successfully before deleting your VM.
Remove-AzureVM -Name "YourVMName" -ServiceName "YourServiceName" -DeleteVHD
Then create a new VM from the image into your existing service.
New-AzureQuickVM -Name "YourVMName" -ImageName "DescriptiveImageName" -Windows -ServiceName "YourServiceName" -InstanceSize "Basic_A2" -WaitForBoot
Since this is a new VM your previous Azure configuration will be gone, you have to create the endpoints for this VM again and so on. If you use a virtual network be sure to specify your Vnet when you create the VM as far as I am aware you can’t change it afterwards.
Tip: If you get a “CurrentStorageAccountName is not accessible” error you have to set your default storage account for the subscription by running:
Get-AzureStorageAccount
Take note of the storage account name then run:
Set-AzureSubscription -SubscriptionName "YourSubscriptionName" -CurrentStorageAccountName "YourStorageAccountName" -PassThru
