Horizontal Autoscaling of Virtual Machines

Introduction to autoscaling

To configure an automatic response to changing demands for resources, you can scale out VMs or scale them in, which is also called horizontal autoscaling. To scale out, the platform clones the base VM and deploys the clones. To scale in, the platform will delete clone VMs and undeploy the base VM. Scaling operations are subject to all standard platform constraints, such as privileges and allocation limits.

• Limitations:

  • Autoscaling does not clone captured VMs, so to use scaling groups with a captured VM, create an instance and recreate the VM. Save VM disks to create an instance template

  • VApp specs do not support scaling groups. See What do virtual appliance specs save and create

  • Scaling groups have aggregate alarms that are associated with the base VM. This means that you can push custom metrics for clone VMs but you cannot create alarms for cloned VMs that are part of a scaling group. 

• State of base VM: A scaling group with a deployed base VM would be destroyed if the base VM were deleted directly on the hypervisor. In contrast, a scaling group with an undeployed base VM is not vulnerable to interference at the hypervisor level

To stop autoscaling, put the scaling group into maintenance mode.

Automatically scale VMs

The platform enables you to automatically scale out (add more VMs) or scale up (add more resources to existing VMs).

To use autoscaling do these steps:

1. Create a base VM, which can be deployed or undeployed

2. Configure the VM and enable metrics

3. Define a scaling group with rules for scaling the VM.
   The checkbox to automatically create a scaling action, will create the following automatically:

   1. Standard alarms and alerts for the selected metrics

   2. Action plans with scaling actions for the VM and triggers for the action plans, which are monitoring alerts

   You can customize the elements the platform creates, or you can create your own configuration.

Related pages:

• Manage Scaling Groups

Define a scaling group

Before you begin:

1. Configure the base VM that will be scaled

2. Ensure that you have enough resources in your virtual datacenter to deploy up to the maximum number of cloned VMs, especially IP addresses

To create a scaling group:

1. Go to Virtual datacenters → Virtual appliances

2. On the VM icon, from the options menu, select Define scaling group

3. Enter the scaling parameters

   

   1. For the Default cooldown, enter the period of time to wait from the start of one scaling operation before allowing another scaling operation

   2. For the Minimum running virtual machines that Abiquo must maintain in the scaling group, the value must be greater than or equal to zero, where zero means that the base machine is not deployed

   3. The option to Keep virtual machines in the same layer can maintain VM anti-affinity layers when autoscaling

   4. Administrators with the privilege to Manage workflow for scaling groups can Disable workflow or enable it as required

   5. Optionally, select Create in maintenance mode to delay the start of autoscaling, and the automatic deployment of VMs to meet the minimum size

   6. Select the option to Create autoscaling action to create basic operations to scale in and scale out, with triggers based on metrics and alarm conditions.

4. Create scaling rules

   

   1. For Scale out rules, enter the number of VMs to Add. This is the number of times to clone the base VM and deploy each clone for each scaling step

   2. For Scale in rules, enter the number of VMs to Remove. Abiquo will delete clone machines and undeploy the base machine

   3. If there is no time range, then this is a default scaling rule. A time range must be unique and cannot overlap with other rules with the same scaling direction. 

5. Click Save

When you save the scaling group, Abiquo will mark the VM icon with the scaling group symbol and display the scaling group name.

• When the scaling group leaves maintenance mode, Abiquo will create clones of the base VM and deploy them to reach the minimum size. 

• The number in the bottom right-hand corner of the icon is the number of running VMs in the scaling group, including the base VM.

To open the scaling group and check its parameters, click the scaling group symbol at the top of the VM icon.

Configure automatic scaling actions

To configure automatic scaling actions:

1. When you define a scaling group, select Create autoscaling action and Save the scaling group

2. In the dialog, select a Metric to control an autoscaling action

   

3. To configure more options, including the thresholds for scaling in and scaling out, click Show more

   

4. To add this action, click Add

5. Add more actions as required 

The platform will automatically create the alarms, alerts, and action plan to automatically scale in or out according to your thresholds.

Trigger autoscaling

Before you begin:

1. Create a VM and a scaling group for the VM. See Manage scaling groups

   1. If you create an automatic scaling action, then the VM metrics will trigger autoscaling when they cross the thresholds set for the actions

To enable autoscaling operations to run:

1. Create an action plan with a scaling action for the VM with the scaling group. See Manage action plans

2. Create triggers to run the action plan. See Manage action plans

When scaling, the platform will search for a scaling rule that is valid for the specific time range, or for a default rule. It will create or delete/undeploy the number of VMs in the rule, then wait for the cooldown period before accepting another scaling request.

How the platform scales VMs

To scale out, the platform does not deploy VMs that are undeployed in the scaling group. To clone the base VM, the platform will do the following:

1. Create disks using the following:

   1. Copies of content of disks from the VM template

   2. Empty disks or volumes for each additional disk used in the VM

   3. Disk controllers used in the VM

2. Apply ALL configuration used in the VM, for example:

   1. CPU and RAM

   2. Network connections of the same type (e.g. private network)

   3. Assignment of firewall policies and attachment to load balancers

   4. Backups, startup script, cloud-init, variables, and so on

   5. Metrics. The group of metrics from clone VMs and the base VM (if it is deployed) can activate alarms in the base VM, even if it is not deployed

   6. Exception – Alarms: the scaling group has only one set of alarms in the base VM

To scale in,  Abiquo currently selects the VMs to delete or undeploy using first in, first out (FIFO). The platform deletes and undeploys VMs without requesting user confirmation when there are disks that are not stored in the Apps library (ISO configuration drive or additional hard disk). 

Perform maintenance on a scaling group

To make changes to your VMs in a scaling group (manually deploy, undeploy, delete, etc.) and edit the scaling group, put it into maintenance mode, which will disable autoscaling. 

When you leave maintenance mode, the platform will apply your modifications to the scaling group, e.g. adding new rules. Then the platform will adjust the number of VMs in the group to within the minimum and maximum size range.

To put the scaling group in maintenance mode:

1. Go to Virtual datacenters → Virtual appliances → select VM

2. At the bottom of the VM icon, click the cog maintenance symbol at the bottom of the VM icon

   

   OR if the scaling group is open, click the spanner maintenance symbol in the top right corner

   

To leave maintenance mode

1. Click a maintenance button

To automatically manage maintenance mode

1. Trigger action plans with the action "Scaling group: start maintenance mode" or "Scaling group: end maintenance mode".

To delete the base VM, you must delete the scaling group first. 

Delete a scaling group

When you delete a scaling group, the platform will place all the VMs in the virtual appliance as regular VMs and the scaling group constraints will no longer exist. 

To delete a scaling group:

1. Go to Virtual datacenters → Virtual appliances

2. Open the scaling group

3. Click the wrench maintenance button to put the scaling group into maintenance mode

4. Click the trash can delete button