Control Costs with Policies

Terraform Cloud estimates costs for many resources found in your Terraform configuration. It displays an hourly and monthly cost for each resource, and the monthly delta. It also totals the cost and delta of all estimatable resources.

In this tutorial, you will enable cost estimation and define policy to check whether the total monthly delta is less than one hundred dollars a month.

»Prerequisites

This tutorial assumes that you are familiar with Terraform Cloud and have an existing test Terraform Cloud workspace configured with AWS access credentials.

If you don't, refer to the Create a Workspace tutorial and Set Up Workspace tutorial to learn more about Terraform Cloud and set up a Terraform Cloud workspace configured with AWS access credentials.

»Verify costs using policies

To verify cost estimates using policies, you need to define your policy and update your policy set.

Add the following configuration to your sentinel.hcl file to declare your new policy in your policy set.

policy "less-than-100-month" {
  enforcement_level = "soft-mandatory"
}

Then, create a new file named less-than-100-month.sentinel that contains the following policy configuration.

import "tfrun"
import "decimal"

delta_monthly_cost = decimal.new(tfrun.cost_estimate.delta_monthly_cost)

main = rule {
    delta_monthly_cost.less_than(100)
}

This policy uses the tfrun import to check that the cost delta for a Terraform run is no more than \$100. The decimal import is used for more precise calculations when working with currency numbers.

Save the updated policy configuration and commit your changes to version control. Terraform Cloud will run checks for both policies defined in sentinel.hcl in all workspaces associated with the policy set.

»Trigger a run

Navigate to the Terraform Cloud workspace for the repostiory and manually queue a new plan.

»View cost estimate

After queueing a new run, Terraform Cloud will estimate changes to your resource costs and display them in the run UI. There you'll find the list of resources, their price details, and the list of un-estimated resources. You'll also find the new total so you can get a sense of the proposed overall monthly cost once the run is applied.

You will also see that the new resource definition satisfies the Sentinel policy check you defined.

Click "Discard run" to cancel the run.

»Next steps

Congrats — you've enabled cost estimation and used it in a policy check! This provides another tool to manage your infrastructure spending.

To learn more about cost estimation, refer to the Cost Estimation documentation.

If you would like to learn more about Terraform Cloud, refer to the following links.

• Learn how to migrate terraform state to Terraform Cloud
• Learn more about Terraform Cloud workspaces
• Read the Terraform Cloud documentation
• Learn about the free and paid features of Terraform Cloud
• Learn more about Cost Estimation Documentation
• Read the Run States Documentation.