Set up Start VM on Connect

Start VM On Connect lets you reduce costs by enabling end users to turn on their session host virtual machines (VMs) only when they need them. You can them turn off VMs when they're not needed.

You can configure Start VM on Connect for personal or pooled host pools using the Azure portal or PowerShell. Start VM on Connect is a host pool setting.

For personal host pools, Start VM On Connect will only turn on an existing session host VM that has already been assigned or will be assigned to a user. For pooled host pools, Start VM On Connect will only turn on a session host VM when none are turned on and additional VMs will only be turned on when the first VM reaches the session limit.

The time it takes for a user to connect to a session host VM that is powered off (deallocated) increases because the VM needs time to turn on again, much like turning on a physical computer. The Remote Desktop client has an indicator that lets the user know the VM is being powered on while they're connecting.

Note

Azure Virtual Desktop (classic) doesn't support Start VM On Connect.

Prerequisites

To use Start VM on Connect, make sure you follow these guidelines:

  • You can only configure Start VM on Connect on existing host pools. You can't enable it at the same time you create a new host pool.
  • The following Remote Desktop clients support Start VM on Connect:
  • If you want to configure Start VM on Connect using PowerShell, you'll need to have the Az.DesktopVirtualization PowerShell module (version 2.1.0 or later) installed on the device you use to run the commands.
  • You must grant Azure Virtual Desktop access to power on session host VMs, check their status, and report diagnostic information. You must have the Microsoft.Authorization/roleAssignments/write permission on your subscriptions in order to assign the role-based access control (RBAC) role for the Azure Virtual Desktop service principal on those subscriptions. This is part of User Access Administrator and Owner built in roles.

Assign the Desktop Virtualization Power On Contributor role with the Azure portal

Before you can configure Start VM on Connect, you'll need to assign the Desktop Virtualization Power On Contributor role-based access control (RBAC) role with your Azure subscription as the assignable scope. Assigning this role at any level lower than your subscription, such as the resource group, host pool, or VM, will prevent Start VM on Connect from working properly. You'll need to add each Azure subscription as an assignable scope that contains host pools and session host VMs you want to use with Start VM on Connect. This role and assignment will allow Azure Virtual Desktop to power on VMs, check their status, and report diagnostic information in those subscriptions.

To assign the Desktop Virtualization Power On Contributor role with the Azure portal to the Azure Virtual Desktop service principal on the subscription your host pool is deployed to:

  1. Open the Azure portal and go to Subscriptions. Select a subscription that contains a host pool and session host VMs you want to use with Start VM on Connect.

  2. Select Access control (IAM).

  3. Select the + Add button, then select Add role assignment from the drop-down menu.

  4. Select the Desktop Virtualization Power On Contributor role and select Next.

  5. On the Members tab, select User, group, or service principal, then select +Select members. In the search bar, enter and select either Azure Virtual Desktop or Windows Virtual Desktop. Which value you have depends on when the Microsoft.DesktopVirtualization resource provider was first registered in your Azure tenant. If you see two entries titled Windows Virtual Desktop, please see the tip below.

  6. Select Review + assign to complete the assignment. Repeat this for any other subscriptions that contain host pools and session host VMs you want to use with Start VM on Connect.

Tip

The application ID for the service principal is 9cdead84-a844-4324-93f2-b2e6bb768d07.

If you have an Azure Virtual Desktop (classic) deployment and an Azure Virtual Desktop (Azure Resource Manager) deployment where the Microsoft.DesktopVirtualization resource provider was registered before the display name changed, you will see two apps with the same name of Windows Virtual Desktop. To add the role assignment to the correct service principal, you can use PowerShell which enables you to specify the application ID:

To assign the Desktop Virtualization Power On Contributor role with PowerShell to the Azure Virtual Desktop service principal on the subscription your host pool is deployed to:

  1. Open Azure Cloud Shell with PowerShell as the shell type.

  2. Get the object ID for the service principal (which is unique in each Azure tenant) and store it in a variable:

    $objId = (Get-AzADServicePrincipal -AppId "9cdead84-a844-4324-93f2-b2e6bb768d07").Id
    
  3. Find the name of the subscription you want to add the role assignment to by listing all that are available to you:

    Get-AzSubscription
    
  4. Get the subscription ID and store it in a variable, replacing the value for -SubscriptionName with the name of the subscription from the previous step:

    $subId = (Get-AzSubscription -SubscriptionName "Microsoft Azure Enterprise").Id
    
  5. Add the role assignment:

    New-AzRoleAssignment -RoleDefinitionName "Desktop Virtualization Power On Contributor" -ObjectId $objId -Scope /subscriptions/$subId
    

Enable or disable Start VM on Connect

Now that you've assigned the Desktop Virtualization Power On Contributor role to the service principal on your subscriptions, you can configure Start VM on Connect using the Azure portal or PowerShell.

To configure Start VM on Connect using the Azure portal:

  1. Sign in to the Azure portal.

  2. In the search bar, enter Azure Virtual Desktop and select the matching service entry.

  3. Select Host pools, then select the name of the host pool where you want to enable the setting.

  4. Select Properties.

  5. In the configuration section, you'll see Start VM on connect. Select Yes to enable it, or No to disable it.

  6. Select Save to apply the settings.

Note

In pooled host pools, Start VM on Connect will start a VM every five minutes at most. If other users try to sign in during this five-minute period while there aren't any available resources, Start VM on Connect won't start a new VM. Instead, the users trying to sign in will receive an error message that says, "No resources available."

Troubleshooting

If you run into any issues with Start VM On Connect, we recommend you use the Azure Virtual Desktop diagnostics feature to check for problems. If you receive an error message, make sure to pay close attention to the message content and make a note of the error name for reference. You can also use Azure Virtual Desktop Insights to get suggestions for how to resolve issues.

If the session host VM doesn't turn on, you'll need to check the health of the VM you tried to turn on as a first step.

For other questions, check out the Start VM on Connect FAQ.