How Parallels RAS Autoscaling works with RDSH based on RAS Template

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This article describes how Parallels RAS auto-scale mechanism works with RDSH Group based on RDSH Template. 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 servers to be added to the group from template:

This is the number of servers available always in the group. E.g. When a group is empty, a server will be added to the group.

Max number of servers to be added to the group from template:

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

Number of servers to be added to the group per request:

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

Drain and unassign servers from group when workload is below (%) and remains below this level for:

This is the workload % of the group required to trigger un-assignment (removal of server from group). 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 RDSH group workload is calculated based on the sessions (active/disconnected). The maximum sessions value configured in the RDSH group properties > Agent 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

maxServerSessions = the limit number of sessions on server multiplied by the number of servers with agent state as OK 

RDSH Group Workload % = (totalSessions * 100) / maxServerSessions

 

How the auto-scale action is triggered

The checks for RDSH template 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

Min number of servers to be added to the group from Template: 1
Max. Sessions 50
Max number of servers to be added to the group from Template: 5
Add new servers from template when workload threshold is above (%): 60
Number of servers to be added to the group per request: 1
Drain and remove servers from group when workload is below (%)  20
and remain below this level for Immediate

 

Scenario

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