Rightsize VMs and Instances

Rightsizing means ensuring that all VMs in your virtualized infrastructure are allocated the correct resources for their workload, with the goal of minimizing cost and maximizing performance. Depending on the cloud platform, you may see CPU, memory or instance type rightsizing recommendations. Rightsizing recommendations are based on VM and guest OS performance data.

Once you've decided a VM should be rightsized, depending on your permissions, you can:

  • Submit a change request to apply the recommendation.
  • Apply the recommendation in the VM's maintenance window.
  • Schedule the recommendation to be applied later.
  • Apply the recommendation immediately.

You may decide to ignore certain recommendations. You may also decide that you don't want to see rightsizing recommendations for particular VMs.

Reasons to rightsize

There are several reasons to rightsize your VMs:

  • Over-allocation wastes expensive server resources and decreases ROI for the infrastructure.
  • Configuring a VM with more virtual CPUs than its workload may cause slightly increased resource usage, potentially impacting performance on very heavily loaded systems. Common examples of this include a single-threaded workload running in a multiple-vCPU VM, or a multi-threaded workload in a VM with more vCPUs than the workload can effectively use. Even if the guest operating system doesn't use some of its vCPUs, configuring VMs with those vCPUs still imposes some small resource requirements that translate to real CPU consumption on the host.
  • Allocating enough memory to hold the working set of applications you'll run in the VM minimizes swap activity and the associated disk thrashing.
  • Allocating more memory than required unnecessarily increases the VM memory overhead, thus consuming memory that could be used to support more VMs.
  • Over-allocation of vCPU causes performance problems on heavily loaded hosts (all vCPUs need to be scheduled to run at the same time).
  • In the VMware context specifically, VMs with less memory and/or fewer vCPUs provide more opportunities for VMware DRS to migrate them in order to improve balance across the cluster. VMs with larger memory sizes and/or more vCPUs add more constraints for migration. It's also easier to manually distribute and balance smaller workloads across the available hosts.

View rightsizing recommendations

A link with the current number of rightsizing recommendations is displayed in the VM Performance widget on the Dashboard.

VM performance widget

You can view all recommendations (including Power Schedule recommendations) by selecting Recommendations in the left-side menu.

Make sure View Active Recommendations is selected.

You can easily filter a long list by entering text in the filter field. For example, in the filter:

  • To view only memory rightsizing recommendations, enter memory.
  • To view only instance type rightsizing recommendations, enter instance type.
  • To view only downsizing recommendations, enter down.

If a user has applied a recommendation, the action is displayed in the Action Taken column. For example, if a user has scheduled a recommendation, "Scheduled" is displayed in the Action Taken column.

Costs associated with recommendations are displayed in your preferred currency.

View recommendations for a single VM

To view recommendations for a single VM, go to the VM's summary page. If there are recommendations, a drop-down panel is displayed. Expand the drop-down panel to view the details.

Make sure View Active Recommendations is selected.

Find VMs with rightsizing recommendations

On the Search page, you can use the following properties to find VMs with recommendations:

  • Has Recommendations
  • Recommendation Annual Cost Savings
  • Recommendations Instance Type Down
  • Recommendations Instance Type Up
  • Recommended CPU Change
  • Recommended Instance Type
  • Recommended Memory Change (GB)

All of these properties are in the Recommendations category.

For example, to find all VMs with a recommendation that will save more than 100 USD per year, search for VMs where the Recommendation Annual Cost Savings is greater than 100. To find all VMs with a recommendation that will cost more than 100 USD per year, search for VMs where the Recommendation Annual Cost Savings is less than -100.

As shown below, use a negative value to find cost increases instead of savings.

Apply rightsizing recommendations

If you decide that a recommendation should be applied, you can submit a change request, apply the recommendation immediately, apply it during your organization's maintenance window, or schedule it for later, depending on your permissions. Submitting a change request is the recommended method, so that the recommendation goes through the request approval process.


  • When a recommendation is applied, running VMs are powered off, reconfigured, and powered on again. Note that if the power-on is unsuccessful, the change isn't reverted. However, if supported by the cloud platform and enabled for the VM, you can rightsize CPU and memory resources while the VM is powered on, within an allowed range.
  • A scheduled recommendation task will be carried out even if the VM's performance changes, or if the recommendation is ignored or rescinded.
  • Because instance type rightsizing recommendations are based on CPU metrics only, we recommend that you check the VM's memory performance before applying a recommendation.
  • If you apply a rightsizing recommendation to a VM that's in an AWS auto scaling group, AWS marks the VM as unhealthy and may terminate and then replace the VM. In this case, the rightsizing task will fail.

To apply a recommendation:

  1. Select one or more VMs.

    Selecting more than one recommendation may limit the available actions.

  2. In the Recommendations menu, the options that appear depend on your permissions:
    • To submit a change request, select Request Service Change. Review the request details, optionally add a comment, and click OK. Comments are displayed in the language they are written in.
    • To apply the changes during this VM's maintenance window, select Apply In Maintenance Window. The time of the next maintenance window is displayed in the dialog.
    • To apply the changes immediately, select Apply Immediately.
    • To apply the changes later, select Schedule. In the Schedule Recommendation dialog, enter a date and time for the recommendation to be applied.

Cancel or edit scheduled recommendations

You can cancel a scheduled recommendation for any VM you own.

When you schedule a recommendation in the VM's maintenance window, you can cancel the scheduled task, but you can't edit it.

When you schedule a recommendation with the Schedule option, you can cancel it and reschedule it.

Any user who is able to see a scheduled rightsizing task can delete it.

To view, cancel or reschedule a scheduled recommendation:

  1. Go to the Tasks page.
  2. Click Scheduled Tasks.
  3. Select the scheduled recommendation
  4. From the Scheduled Tasks menu, select a command.

For more information, see Delete scheduled tasks.

Ignore rightsizing recommendations

If you decide that a recommendation shouldn't be applied, you have a few options. When you click Ignore for a recommendation you can:

  • Ignore the recommendation for a specified number of days. The recommendation disappears from the list. After the specified number of days has passed, another recommendation may be made.
  • Ignore the recommendation until new performance data is available. The recommendation disappears from the list. After the required number of samples have been acquired for the VM, a new recommendation of this type may be made.

For a VM that's always powered on, it doesn't matter which of these two options you pick, because performance data is gathered nightly for powered-on VMs. For a VM that's only powered on one day per month, though, if you chose the second option, it would take longer to make a recommendation.

You can also ignore a recommendation forever. The recommendation disappears from the list.  No more recommendations of the same type and direction for this VM will be generated. For example, if you ignore a Memory Upsize recommendation forever, Memory Downsize, CPU Upsize, and CPU Downsize recommendations may still be generated for this VM.

Prevent recommendations for a VM

If you don't want to see recommendations for a particular VM, you can exclude the VM from rightsizing recommendations.

To prevent the generation of recommendations for a VM:

  1. Select one or more VMs.
  2. In the Recommendations menu, select Exclude VM.
  3. In the Exclude VM dialog, enter a reason and click Exclude VM.

Allow new recommendations after ignoring or excluding

If you change your mind after you ignore a recommendation, you can allow new recommendations of that type. In this case, the recommendation you originally ignored is closed.

Likewise, if you change your mind after you exclude a VM from rightsizing recommendations, you can remove the exclusion, so that you'll see recommendations for the VM.

To allow new recommendations for a VM after a recommendation has been ignored, or a VM has been excluded from recommendations:

  1. Click View Ignored Recommendations.
  2. Select one or more VMs.

    If your selection includes both an Ignored and Excluded recommendation, no action can be taken.

  3. For a VM with ignored recommendations, in the Commands menu, click Allow New Recommendations.

    The VM disappears from the Ignored Recommendations list, the original recommendation is closed, and another recommendation for this VM can be generated.

  4. For a VM that has been excluded from recommendations, in the Commands menu, click Remove Exclusion.

    The VM disappears from the Ignored Recommendations list, and recommendations for this VM can now be generated.

    There's a wait period of five minutes before new recommendations are generated.

Handle conflicting recommendations

You may occasionally see conflicting recommendations. For example, the VM metrics may result in an upsize recommendation, while the guest OS metrics result in a downsize recommendation. If this occurs, both recommendations are displayed, so that you can view the details and decide which one to apply.

View a VM's rightsizing group

All VMs belong to a rightsizing group. The rightsizing group determines the rules used to generate rightsizing recommendations.

To add the Rightsizing Group property to the VM Details drop-down panel:

  1. On the service's summary page, click on the Details drop-down panel.

    The Property Selection dialog appears, displaying the list of properties that are available and displayed in the Details drop-down panel.

  2. In Property Selection dialog, under Available Properties, choose Recommendations > Rightsizing Group.
  3. Use the arrows or drag and drop to move the Rightsizing Group property to Displayed Properties.

    The Rightsizing Group is now displayed.