How Parallels RAS Autoscaling works with Azure Virtual Desktop

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This article describes how Parallels RAS auto-scale mechanism works with Azure Virtual Desktop (AVD). When creating new or adding an existing host pool, Parallels RAS allows to configure the following auto-scale settings:

 

 

Available settings

Setting name Explanation

Min number of hosts to be added to the host pool from Template:

This is the number of hosts available always in the host pool. E.g. When host pool is empty, a host will be added to host pool.

Max number of hosts to be added to the host pool from Template:

This is the number of maximum hosts a host pool is allowed to have. At no time the number of hosts in a host pool should exceed this number.
Add new hosts from template when workload threshold is above (%): This is the workload % of the host pool required to trigger a request (refer to workload calculation explained below).

Number of hosts to be added to the host pool per request:

This is the number of hosts to be added per request, if the number of hosts to be requested is going to exceed the maximum number of allowed hosts, the auto-scaling engine only adds the required hosts.

Drain and remove hosts from host pool when workload is below (%) and remains below this level for:

This is the workload % of the host pool required to trigger un-assignment (removal of host from host pool). If remains below is not set to immediate, then it will only trigger the un-assignment if the workload % of host pool is still below after the remains below time has elapsed. Please note that if in between the first un-assignment trigger and the second check after the remains below time has elapsed the workload % meets the request criteria, the un-assignment request is discarded.

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Workload calculation

The host pool workload is calculated based on the sessions (active/disconnected). The maximum sessions value configured in the host pool settings is taken into consideration as well. Sessions currently running on the hosts can be viewed from the Site Info page or from the session management page in the Farm category section.

totalSessions = total running sessions (active/disconnected) from all hosts in host pool

maxHostPoolSessions = the limit number of sessions on host multiplied by the number of Hosts with agent state as OK 

Hostpool Workload % = (totalSessions * 100) / maxHostPoolSessions

 

How the auto-scale action is triggered

The checks for AVD requests and un-assignment are triggered by one of the following scenarios:

Note: Only the primary Publishing Agent of each site will trigger/process the mentioned checks. The check is not triggered immediately when the apply notification is received because there might be agents that need to be redistributed in a multiple Publishing Agents environment.

 

Example



Given environment

Host pool type: Pooled
Provision type:  Template
Load balancer Breadth
Min number of hosts to be added to the host pool from Template: 1
Limit number of sessions per host 50
Max number of hosts to be added to the host pool from Template: 5
Add new hosts from template when workload threshold is above (%): 60
Number of hosts to be added to the host pool per request: 1
Drain and remove hosts from host pool when workload is below (%)  20
and remain below this level for Immediate

 

Scenario

 

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