# Power Management Auto Scaling in AVD Click [here](https://github.com/MicrosoftLearning/AZ-140-Configuring-and-Operating-Microsoft-Azure-Virtual-Desktop/blob/master/Instructions/Labs_EntraID/05_LAB_41_02_Implement_autoscaling_of_session_hosts.md) for the github version of Microsoft ESI lab. Configure autoscaling for an Azure Virtual Desktop environment to optimize resource utilization by dynamically scaling session hosts based on demand. **Note:** To enable autoscale for Azure Virtual Desktop, you must grant the service principal permissions to manage the power state of session host VMs. This is done using the built-in **Desktop Virtualization Power On Off Contributor** RBAC role. Ensure that this role is assigned at the **subscription scope**—assigning it at a lower level (e.g., resource group, host pool, or VM) will prevent autoscale from functioning correctly. This role differs from **Desktop Virtualization Power On Contributor**, which is used in the *Manage host pools and session hosts* lab to support *Start VM on Connect* functionality. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1739817911168/61786d84-bcc6-48ac-9b1b-07bedbd0abe5.png align="center") There are two scaling methods, but now let's focus on **Power Management Autoscaling**: ### **Power Management Autoscaling** * VMs are only turned on or off to adjust capacity. * This is the only option if your host pools **do not** use session host configuration. ### **Dynamic Autoscaling (Preview)** * Manages capacity by both **turning on/off existing VMs** and **creating/deleting VMs** as needed. ### Evaluating Azure Virtual Desktop Autoscale Functionality #### Case Overview The evaluation of the Azure Virtual Desktop (AVD) autoscaling functionality was performed by configuring a host pool with predefined scaling settings. The goal was to observe how the system dynamically adjusted session hosts based on user demand and predefined parameters. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1739818873598/f69482d0-b97b-40a4-990e-5e7488205dfe.png align="center") #### Initial Setup The host pool (az140-21-hp1) was configured with three session hosts. The following settings were established to facilitate testing: **Max session limit**: Set to 1 to illustrate autoscaling behavior(HP Setting\\Properties). ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1739819199423/b788201f-dcb3-432c-9bf3-17266c0449ee.png align="center") **Note**: The schedule effectively covers every day of the week, which will facilitate evaluating outcome of autoscaling. * **Scaling plan**: Created with ramp-up, peak, ramp-down, and off-peak hours for week days and specified autoscaling triggers. Scaling plan must include an associated schedule for at least one day of the week.. * Ramp-up Start time here: one hour less than our current local time * ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1739819747860/04c9f999-e33d-481f-8d4d-ead682cd0b41.png align="center") **Note:** The *Minimum percentage of hosts* setting determines the lowest percentage of session hosts to maintain as running during ramp-up and peak hours. For example: * If the minimum is set to **30%** and your host pool contains **3 session hosts**, Autoscale will ensure at least **1 host** (30% of 3, rounded up to the nearest whole number) remains active and available to handle user connections. **Note:** For pooled host pools, autoscale overrides any existing load-balancing algorithms configured in your host pool settings. Instead, it applies load balancing based on the schedule configuration you define. * **Capacity thresholds**: * Ramp-up and peak hours: 60% * Ramp-down and off-peak hours: 80% * **Minimum active hosts**: * Ramp-up: 30% of total session hosts (rounded up to 1 host). * Ramp-down: 10% of total session hosts (rounded up to 1 host). * **Note:** The *Capacity Threshold* setting defines the percentage of used host pool capacity that triggers Autoscale to evaluate whether additional session hosts should be turned on or off during ramp-up and peak hours. For example: * If the capacity threshold is set to **60%** and your host pool has a capacity of **1 session** (with one host running), Autoscale will activate additional session hosts once the host pool’s load (load= user actively using the session) exceeds **60%** (which, in this case, is equivalent to 100% utilization). Peak hours start time here is: Current time + 1 hours ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1739830624248/0168c781-7cec-4936-a5fe-decafd086507.png align="center") **Note**: The **Capacity threshold (%)** setting is shared between the **Ramp-up** and **Peak hours** settings. **Ramp Down:** * Ramp-down start time here is: Current time + 2 hours * **Note:** The *Minimum Percentage of Active Hosts (%)* setting specifies the lowest percentage of session host virtual machines to maintain during ramp-down and off-peak hours. For example: * If the minimum percentage is set to **10%** and your host pool contains **3 session hosts**, Autoscale will ensure at least **1 session host** (10% of 3, rounded up) remains active to handle user connections. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1739820296864/11e2eac2-1234-49d2-b6ec-d2b02aacf3c1.png align="center") **Note:** The *Capacity Threshold (%)* setting defines the percentage of used host pool capacity that Autoscale uses to determine when to turn off virtual machines during ramp-down and off-peak hours. For example: * With **1 user connection** and **3 hosts running**, if the capacity threshold is set to **80%**, Autoscale will turn off **1 host**, reducing the used capacity to **50%**. Off-peak hours start time here is: Current time + 3 hours ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1739820328935/4770894c-a530-4d0c-a9e1-dc28166d0455.png align="center") **Note:** Autoscale stops and deallocates session hosts based on the following rules: 1. The used host pool capacity is below the defined **Capacity Threshold**. 2. Turning off session hosts will not cause the used capacity to exceed the **Capacity Threshold**. 3. Autoscale only deallocates session hosts with no user sessions, unless: * The scaling plan is in the **ramp-down phase**, and * The setting to **force user logoff** is enabled. 4. During the **ramp-up phase**, pooled Autoscale will not turn off session hosts to ensure user experience remains unaffected. **Note**: The **Capacity threshold** setting is shared between the **Ramp-down** and **Off-peak hours** settings. --- ## Autoscaling Evaluation 1. **Evaluate the Ramp-up Settings:** * Review the **Power state** of the session hosts and verify that one host is listed as **Running**. * **Note:** It may take a few minutes for the first session host to reach the **Running** state. * **Note:** This behavior is expected. Based on the **Ramp-up settings** of the newly created scaling plan, at least **one session host** must remain online at all times. > Currently: > > * The host pool capacity is **1** (with only 1 host running). > > * The used host pool capacity is **0%**, as there are no active user connections. > 2. **Evaluate the Ramp-up and Peak Hours Capacity Threshold:** * Start using a session (full desktop or remote app) **Note:** At this point, the used host pool capacity is now **100%**, exceeding the **60% capacity threshold**. Autoscale will activate another host, reducing the used capacity to **50%**. Since this is below the threshold, the third host will remain **stopped/deallocated**. You will verify this behavior in the next steps. 3. **Verify Autoscaling Behavior:** * On the **host pool | session hosts** page, select **Refresh**. * Verify that **two session hosts** are now listed as **Running**. 4. **Evaluate the Ramp-down Capacity Threshold:** * In the **week\_schedule** pane navigate to the **Ramp-down** tab and adjust the **Start time** to a time between the **Peak hours Start time** and the current time. * **Note:** You may need to adjust the **Peak hours Start time** as well. 5. **Log Off and Verify Ramp-down Behavior:** * Switch to the **Command Prompt** window and enter the following command: **logoff** * Return to the Azure portal and navigate back to **az140-21-hp1 | Session hosts**. * Verify that only **one session host** remains **Running**. * **Note:** It may take 1-2 minutes for the session host to shut down. --- ### **Example Scenario** * **Minimum Percentage of Hosts**: * **Ramp-Up**: 20% of hosts must remain active. * **Ramp-Down**: 10% of hosts must remain active. * **Load Balancing Algorithm**: * **Ramp-Up**: Breadth-first (sessions distributed evenly across hosts). * **Ramp-Down, Peak Hours, and Off-Peak Hours**: Depth-first (sessions assigned to the first available host until it reaches capacity). With **2 hosts** and each host supporting up to **4 sessions**, here’s the table and explanation: --- ### **Updated Table** | **Phase** | **Active Hosts** | **Capacity Threshold** | **Sessions per Host** | **Load Balancing** | **Description** | | --- | --- | --- | --- | --- | --- | | **Ramp-Up** | Active hosts **≥** 20% | Host capacity **<** 60% | ≤ 2 sessions per host | Breadth-first | Hosts are activated, and sessions are distributed evenly across hosts. | | **Peak Hours** | Active hosts **\=** 100% | Host capacity **≤** 60% | ≤ 2 sessions per host | Depth-first | Both hosts are active, and sessions are assigned to the first available host. | | **Ramp-Down** | Active hosts **≥** 10% | Host capacity **<** 90% | ≤ 3 sessions per host | Depth-first | Hosts are deactivated gradually, and sessions are assigned to the first host. | | **Off-Peak Hours** | Active hosts **≥** 10% | Host capacity **<** 90% | ≤ 3 sessions per host | Depth-first | Only the minimum required host is active, handling sessions depth-first. | --- ### **Key Adjustments** 1. **Minimum Percentage of Hosts**: * **Ramp-Up**: 20% of 2 hosts = **1 host** must remain active. * **Ramp-Down**: 10% of 2 hosts = **1 host** must remain active. 2. **Load Balancing Algorithm**: * **Ramp-Up**: **Breadth-first** ensures sessions are distributed evenly across hosts. * **Ramp-Down, Peak Hours, and Off-Peak Hours**: **Depth-first** assigns sessions to the first available host until it reaches capacity. 3. **Capacity Threshold**: * **Ramp-Up and Peak Hours**: 60% capacity = **2 sessions per host**. * **Ramp-Down and Off-Peak Hours**: 90% capacity = **3 sessions per host**. --- ### **Example Scenario** Let’s walk through a typical day with **2 hosts** and **up to 4 sessions per host**: #### **Ramp-Up (Morning)** * **Active Hosts**: 1 host (20% of 2 hosts). * **Sessions per Host**: Up to 2 sessions per host (60% capacity). * **Load Balancing**: Breadth-first (sessions distributed evenly). * **What Happens**: * If there are 2 sessions, both are assigned to the first host. * If there are 3 sessions(%75 > %60), the first host gets 2 sessions, and the second host gets 1 session. #### **Peak Hours (Midday)** * **Active Hosts**: 2 hosts (100% of hosts). * **Sessions per Host**: Up to 2 sessions per host (60% capacity). * **Load Balancing**: Depth-first (sessions assigned to the first available host). * **What Happens**: * New sessions are assigned to the first host until it reaches 2 sessions. * Once the first host is full, new sessions are assigned to the second host. #### **Ramp-Down (Evening)** * **Active Hosts**: 1 host (10% of 2 hosts). * **Sessions per Host**: Up to 3 sessions per host (90% capacity). * **Load Balancing**: Depth-first (sessions assigned to the first available host). * **What Happens**: * The remaining host handles up to 3 sessions. * If there are 4 sessions, the first 3 are assigned to the active host, and the 4th session may wait or trigger activation of the second host temporarily. #### **Off-Peak Hours (Night)** * **Active Hosts**: 1 host (10% of 2 hosts). * **Sessions per Host**: Up to 3 sessions per host (90% capacity). * **Load Balancing**: Depth-first (sessions assigned to the first available host). * **What Happens**: * The active host handles up to 3 sessions. * If there are more than 3 sessions, the system may temporarily activate the second host. --- ### **Why This Configuration Works** * **Ramp-Up (Breadth-first)**: * Ensures sessions are distributed evenly across hosts, preventing overloading a single host. * **Peak Hours, Ramp-Down, and Off-Peak Hours (Depth-first)**: * Optimizes resource utilization by filling one host at a time before moving to the next. * **Minimum Percentage of Hosts**: * Ensures at least one host is always active to handle sessions, even during low-demand periods. --- ### **Summary** With **2 hosts** and **up to 4 sessions per host**, the system dynamically scales resources based on demand: * **Ramp-Up**: 1 host active, sessions distributed evenly (breadth-first), up to 2 sessions per host (60% capacity). * **Peak Hours**: 2 hosts active, sessions assigned depth-first, up to 2 sessions per host (60% capacity). * **Ramp-Down**: 1 host active, sessions assigned depth-first, up to 3 sessions per host (90% capacity). * **Off-Peak Hours**: 1 host active, sessions assigned depth-first, up to 3 sessions per host (90% capacity).