Documentation and Best Practices

Learn how to use Cloudability and get the most out of our cloud cost management tool

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About Rightsizing

For the latest version of this help, see:

The Rightsizing feature allows you to optimize cost by building and scaling your cloud infrastructure tightly around your needs. Since cloud vendors bill you for services you provision rather than what you consume, underutilized resources will cause you to incur excessive spend that you can avoid by moving to resources that better match your environment.  Rightsizing allows you to view resource utilization over time, along with recommended actions for savings. You can view multiple recommended scenarios per resource, each of which features associated risk level and savings value. Use this information to better inform your cloud rightsizing decisions.

Rightsizing Overview Page

To access the Rightsizing feature, click Optimize > Rightsizing. Then, select your desired cloud vendor and service.

NOTE: Recommendations are not yet available for Amazon S3, RDS, and Redshift.


The main table shows all resources with spend in the specified time period. You can choose between the last 10 days or the last 30 days. 10 days is the recommended time period for most users. Resources are sorted by cost savings by default. Start at the top of the list to see the underutilized resources with the highest potential savings.

TIP: Visit the blog to see when you should review spend over the last 10 days vs. the last 30 days.


For each resource, the table displays account information, resource type, and the resource’s associated idle value. Cost (Total) shows your spend over the selected time period, which potentially includes committed use discounts, custom pricing, and for Amazon EC2, any spot usage in the billing for that resource.

NOTE: See the FAQ to learn how CLDY defines Idle and how spend is determined.

The following recommendations are displayed in the Actions column:

  • Rightsize - Resize to the resource type specified in the New
  • Terminate – Terminate your resource because it is predominately idle.
  • Autoscale - Set up autoscaling for the resource.
  • No Action - Do not take any action on the resource at this time.
  • Incomplete Util Data
    • Ensure that your policy is up to date with the latest permissions, or
    • Determine if the resource was active for less than an hour, as it may not appear in the Describe Data cache from AWS

Select a Cost Basis

Select a cost basis to determine how recommendations are calculated. Two cost basis options are available: On-Demand and Effective. If your organization has enabled Custom Pricing within Cloudability, the relevant custom rates will be applied to the cost basis calculations.


  • On-Demand - This basis provides a direct comparison between the instance listed in the Current column and the instance recommended in the New column based purely on On-Demand Pricing. Any potential impact from Reserved Instances (RIs) or Savings Plans (SPs) is not included.  Note that the On-Demand Prices shown will reflect any custom pricing agreements you have configured within Cloudability. This is the default option.
  • Effective - This basis takes into account the historical impact of Reserved Instances (RIs) and Savings Plans (SPs) for the purpose of calculating the cost for the Current instance type over the reporting period. You can think of this in a similar manner to the Cost(Amortised) metric in that all associated upfront and recurring costs are included. In other words, this was the Effective cost of running your current instance. For the recommended “New” instance type, the cost figures are based on the On-Demand prices. This is because the New configuration may not benefit from RIs or SPs. This comparison is the more conservative option. Even if you inadvertently move away from RIs/SPs, your new overall rate will still be better. As a result, the overall savings reported using this methodology will sometimes be lower. Custom pricing will be applied to these figures if applicable.

Use the On-Demand basis if you are looking to remove the unpredictable nature of commitment-based discounts from your analysis and to maximize the number of recommendations provided to you. Use the Effective basis if you prefer to base your recommendations on the historical True Cost of running your instances and to take a conservative approach. To optimize your RI spend, see Reserved Instances.

Export overview table to see additional details

Click Export on the Overview Page to view additional details for all resources. The spreadsheet includes additional account information including region, operating system, tags available per resource, and the Effective Rate for the current and new resource types.

View utilization time trends

To know how to rightsize your resources, you will need up-to-date information on the utilization of each resource. Click the Details button at the right of each row in the main table to view time trends of utilization metrics relevant to each service. For compute instances (for example, Amazon EC2 or Azure Compute), Cloudability plots CPU (%), Network (Mbps), Disk (MB/S), and Memory (%). See the glossary to understand the source of each metric.


Each utilization metric uses peak values as opposed to average values. Average values are problematic because they are more likely to lead you to move your workload to an instance that does not have enough capacity, which results in ‘clipping’.


View recommendations

To give you the greatest flexibility when rightsizing your infrastructure, Cloudability provides multiple recommendations per resource. You can model each recommended resource against your current utilization. The details page displays up to five recommendations. Click each recommendation to toggle the recommended yellow-dashed line on the chart.

Recommendation Order

Rightsizing gives you the opportunity to balance risk (likelihood of resource ‘clipping’) versus savings. The recommendations are arranged from left to right, with the left-most option being the top Cloudability recommendation. This recommendation is the highest savings option at the lowest risk level. The additional recommendations will often have higher potential savings and higher risk. Subsequent recommendations are ordered with highest-savings, higher-risk categories preceding lower-risk, second-highest-savings options.


Filter recommendations

Recommendations can shift based on the requirements of your organization. For example, for Amazon EC2, Cloudability recommends the newest generation instances by default. But, you may have special pricing or an infrastructure need that requires you to resize only to prior generation instances. Likewise, you may prefer to stay within the same instance family for ease of resizing, as is the case for some Azure Compute workloads. You can select filter options on the Details Page that will update the recommendations.


For Amazon EC2, the options are:

  • Show current generation - recommendations are restricted to the latest instance families
  • Equivalent memory capacity - for cases where the memory metric is not available for the resource
  • Remain in instance family - recommendations are restricted to current instance family

How are the recommendations calculated?

For any particular resource, Cloudability first finds all candidate recommendations. For example, for a compute instance, this would include all instance types that are available for the particular Region and OS used in the original workflow. The candidate set is then limited to those which have a lower hourly (On-Demand or Pay-as-you-go) price relative to the effective rate paid over the prior ten days.

Proprietary algorithms then model the performance of the existing workload on each element in the candidate set of recommendations, taking key performance characteristics as well as theoretical and empirical performance limits into account. The algorithms return a ranked list of recommendations, with scores for both Savings and Risk, enabling you to run your infrastructure with maximum efficiency.








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