Control your Azure Virtual Desktop costs with Scaling Plans

Cloud Computing has changed the way we approach our enterprise infrastructure.

The amount of options available to us now means that we can finally ditch that dusty old server sitting the the bottom of the server rack (or in some cases at the back of a cupboard) for a modern secure solution that we don’t need to sit and pray in front of every time we need to restart it.

The Problem with the Cloud

But …. some people would prefer to keep old “Dusty Springfield” alive because the effort to migrate and in some cases re-architect the service is too much and too costly. And thats the thing we hear the most when a suggestion to migrate to a cloud service is raised – “the cloud is very expensive…”.

And lets be honest, it is …..

Money money money ……

There, I said it. Out Loud. In Print. Cloud Computing is expensive. There’s a helicopter hovering over my house at the minute but I’m sure its nothing to worry about ……

In all seriousness though, when scoping out a Cloud solution the first thing that is looked at is cost. You can argue as much as you want about the redundancy, the lower power and cooling costs, lack of hardware costs etc. The bean counters will look at the bottom line and say “we’re not paying that much now….”. And “Dusty Springfield” limps on defiantly in corner.

Of course, your cloud computing costs are defined by the options you select and what level of redundancy you need. Scale Sets, Storage redundancy across zones and regions. Or just keep it as locally redundant storage? Then you get into the sizing of your solutions.

How the Costs add up

Azure Virtual Desktop is one of those cool technologies that can help you provide a secure environment for your users to access Cloud or Hybrid environments in a consistent and unified experience. But because its built on underlying VMs which you need to size based on your requirements, the costs can mount up.

Lets take a look at an example of a standard Azure Virtual Desktop host pool that contains 10 Session Hosts which are delivering Remote Apps to 100 users. The Session Hosts are generally sized from the General Purpose VM type and the most common one used is the “Standard_D4s_v3”, which has 4 vCPU’s and 16GB memory.

The base cost for this VM if you create a standard Azure Virtual machine comes in at approx $160 per month.

Standard Virtual Machine Type

However, if we use this VM type for our Azure Virtual Desktop Session Hosts with Windows 10 Enterprise Multi-Session version 21H2 with Microsoft 365 Apps installed, the cost then jumps to $290 per month.

Azure Virtual Desktop Virtual Machine Type

So, lets go back to our 10 Session Hosts – at that price we’re talking $2900 per month, or just under $35000 per year. And thats for just 10 VMs in the environment. And thats why Cloud Computing is expensive! Of course, this doesn’t take into account reserved instances or spot instances, but you get the idea.

The $290 per month cost for a VM isn’t based on a cost per month – its based on 730 hours of usage or 24 hours multiplied by just over 30. This where you can start cutting into that $35000 per year cost, and where Scaling Plans applied to your Azure Virtual Desktop Host Pools can help.

Scaling Plans

Scaling Plans lets you scale your session host virtual machines (VMs) in a host pool up or down to optimize deployment costs. You can create a scaling plan based on:

  • Time of day
  • Specific days of the week
  • Session limits per session host

You follow the guidelines below when creating your scaling plan:

  • At the time of writing, you can only configure autoscale with existing Pooled host pools. This won’t work with Personal host pools
  • You must create the scaling plan in the same Azure region as the host pool you assign it to.
  • All host pools you use with autoscale must have a configured MaxSessionLimit parameter. Don’t use the default value.
  • You must grant Azure Virtual Desktop access to manage the power state of your session host VMs.

Create a custom RBAC role

Now that we know the benefits and rules, the first thing we need to do is create a custom RBAC role. This custom role and assignment will allow Azure Virtual Desktop to manage the power state of any VMs in those subscriptions. It will also let the service apply actions on both host pools and VMs when there are no active user sessions.

The steps for creating the Custom RBAC Role are as follows (this is the same for creating any Custom RBAC Role):

  • First, create a json file using whatever your favourite editor is (I’m using Sublime in this example). Save the file as avdscale.json and add the following information into it:
  • Open the Azure portal and go to Subscriptions and select a subscription that contains a host pool and session host VMs you want to use with autoscale. Select Access control (IAM). Select the + Add button, then select Add custom role from the drop-down menu.

  • On the “Basics” screen, go to Baseline permissions and browse to the avdscale.json file that you just created.
  • This will import all of your settings, so on the next screen you will see the permissions that you had specified in your json file.
  • Next, we have “Assignable Scopes”. You want to assign this at subscription level as assigning this custom role at any level lower than your subscription, such as the resource group, host pool, or VM, will prevent autoscale from working properly.
  • We can now skip to the “Review and Create” screen, as this will validate and list out our permissions for the RBAC role. Review these and then click “Create”:
  • And once thats created, we can see its been created as a Custom Role:

  • Now we need to add a Role Assignment for our RBAC Role. So we click on “Add role assignment”

  • We select our Custom RBAC role and in the members screen, we choose to assign access to a User, group or service principal. From the select members screen, search for “Windows Virtual Desktop”
  • Go to “Review and Assign” and click create:
  • And we can see that at subscription level the role has been assigned:

Create our Scaling Plan

Now that our RBAC role is done, we can create our scaling plan.

  • Open the Azure portal. In the search bar, type Azure Virtual Desktop and select the matching service entry. Select Scaling Plans, then select Create.
  • On the Basics screen, provide the following:
    • Subscription and Resource Group where the Scaling Plan will be created
    • Name
    • Location (remember this needs to be in the same region as your Host Pool)
    • Time Zone

The other entries are optional, however an important one to note is Exclusion Tags – you can use this in conjunction with Tags to excluse certain VMs from autoscaling operations

  • Click next and this will bring you to the Schedules screen. Click on Add Schedule
  • In the General screen, we enter a Schedule Name and also select the days we want the schedule to apply to.
  • In the Ramp-up screen, we specify a default starting point.
    • So in this instance, we want to have 20% (or 2 out of our 10 Session Hosts) powered on and ready to accept connections at 08:00.
    • We’ve selected “Breadth First” for Load balancing – this means users will be spread evenly across available hosts and is recommended for consistent performance.
    • Finally, we have set a Capacity threshold of 80%. If you recall, we set our hosts to accept a maximum of 10 connections. We have 2 hosts powered on, so once we reach 16 users across those 2 hosts, the next host will automatically power on.
  • Next up is Peak hours. For this we specify a starting time (which is normally when the majority of your users will be logging on) and we’ve also flipped the Load Balancing to “Depth-first”, which will load up all available hosts with user sessions (up to our 80% threshold) before bringing another one online. This is really up to you as to how you want to load balance, but as a reminder:
    • Breadth-first load balancing distributes new user sessions across all available session hosts in the host pool.
    • Depth-first load balancing distributes new sessions to any available session host with the highest number of connections that hasn’t reached its session limit yet.
  • Next up is Ramp-down, this is where we start deallocating hosts at the end of the working day and as you can see, the target is to get back down to 20% of the hosts. The important point to make here is the “Force logoff users” option. If this is enabled then the following applies:
    • This will choose the session host with the lowest number of user sessions to shut down. Autoscale will put the session host in drain mode, send all active user sessions a notification telling them they’ll be signed out, and then sign out all users after the specified wait time is over. After autoscale signs out all user sessions, it then deallocates the VM.
    • During ramp-down, autoscale will only shut down VMs if all existing user sessions in the host pool can be consolidated to fewer VMs without exceeding the capacity threshold.
  • Finally, we get to “Off-peak hours” which is the end of the “Ramp-down” period.
  • And thats our weekday schedule created. You can also go back in and create a weekend schedule where you can bring the number of hosts down to 10% and have a higher capacity threshold at weekends:
  • Once the schedules are created, we assign the Scaling Plan to our Host pool and click on “Enable autoscale”:
  • And now we can validate our options and click on “Review and create”:

Give all of this about an hour to kick in and you will see your Azure Virtual Desktop session hosts automatically deallocated as per your schedules if not in use!

Money money money ….

Earlier in this post, I gave a yearly figure of approx $35000 to run our 10 Session Host VMs. However, that figure is based on full consumption. So lets do some very quick calculations to see how our scaling plan affects that figure:

  • As we said, a single VM running at full consumption (or the full 730 hours) will cost us $290 per month.
  • Based on our schedules created above, we’re going to have 1 VM running full time for both weekdays and weekends. So thats $290 per month, or $3,480 per year.
  • We’re then guaranteed to have 1 VM running from Monday until Friday for 24 hours, and also on weekends for 12 hours each day (depending on how schedule is created). Thats effectively 6 days a week instead of 7. So we need to calculate that over a year which is a case of getting 6/7ths of our full price figure. Thats coming in at $2,983 per year for that VM.
  • Now, its back to the other 8 VMs and the 100 users who are using this. “If” those 100 users are logged on, the other 8 VMs will be up for 12 hours a day from Monday to Friday only as per our schedule. So for that, we need to get 5/7ths of our full price figure (which is $2,486) and then half it because we’re only using for 12 hours a day (and thats coming in at $1,243 per VM).

In summary, what we’ve got is:

  • $3,480 – 1 VM at full consumption
  • $2,983 – 1 VM at slightly reduced consumption for weekdays and weekends
  • $9,944 – 8 VMs running for 12 hours a day from Monday to Friday

Add those figures up and you get a total of $16,407. And we need to remember, that figure doesn’t available cost reductions like Reserved Instances or Hybrid Benefit.

Conclusion

So by implementing a Scaling Plan for the Host pool above, we’ve saved ourselves nearly $20,000. Again I’m going to stress the figures I’m quoting here are approximate, may not represent what you see in your own personal or enterprise subscriptions, and should not be taken as exact savings. Make sure to speak to your Microsoft TAM or Cloud Service Provider for more details. You can find out more about scaling plans here.

Hope you enjoyed this post, until next time!

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