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Control Costs with Sentinel Policies

Step-01: Introduction

  • We are going to learn the following in this section
  • Sentinel Cost Control Policies
  • Apply them for Ec2 Instance and verify pass and fail cases

Step-02: Review Sentinel Cost Control Policies

Step-02-01: less-than-100-month.sentinel

  • This policy uses the tfrun import to check that the new cost delta is no more than \$100
  • The decimal import is used for more accurate math when working with currency numbers. 
    import "tfrun"
import "decimal"

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

main = rule {
    delta_monthly_cost.less_than(100)
}

Step-02-02: sentinel.hcl

policy "less-than-100-month" {
  source  = "./less-than-100-month.sentinel"
  enforcement_level = "soft-mandatory"
}

Step-03: Copy Sentinel Cost Control Policies to terraform-sentinel-policies git repo

  • Copy folder terraform-sentinel-cost-control-policies to Local git repository terraform-sentinel-policies
  • Check-In code to Remote Repository 
    # GIT Status
git status

# Git Local Commit
git add .
git commit -am "Sentinel Cost Control Policies Added in new folder"

# Push to Remote Repository
git push

# Verify the same on Remote Repository
https://github.com/stacksimplify/terraform-sentinel-policies.git

Step-04: Add new Sentinel Policy Set in Terraform Cloud

  • Go to Terraform Cloud -> Organization (hcta-demo1) -> Settings -> Policy Sets
  • Click on Connect a new Policy Set
  • Use existing VCS connection from previous section github-terraform-modules which we created using OAuth App concept
  • Choose Repository: terraform-sentinel-policies.git
  • Name: terraform-sentinel-cost-control-policies
  • Description: terraform sentinel cost control policies
  • Policies Path: terraform-sentinel-cost-control-policies
  • Scope of Policies: Policies enforced on selected workspaces
  • Workspaces: terraform-cloud-demo1
  • Click on Connect Policy Set

Step-05: Review our first Terraform Cloud Workspace

  • Go to Terraform Cloud -> Organization (hcta-demo1) -> workspace (terraform-cloud-demo1)

Step-05-01: Configre Environment Variables in Terraform Cloud for AWS Provider

  • Setup AWS Access Keys for Terraform
  • Go to Organization (hcta-demo1) -> Workspace(terraform-cloud-demo1) -> Variables
  • In environment variables, add the below two
  • Configure AWS Access Key ID and Secret Access Key
  • Environment Variable: AWS_ACCESS_KEY_ID
  • Key: AWS_ACCESS_KEY_ID
  • Value: XXXXXXXXXXXXXXXXXXXXXX
  • Environment Variable: AWS_SECRET_ACCESS_KEY
  • Key: AWS_SECRET_ACCESS_KEY
  • Value: YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY

Step-05-02: Pass Case: Queue Plan and Verify Cost Control Policies Applied

  • Go to Organization (hcta-demo1) -> Workspace(terraform-cloud-demo1)
  • Queue Plan -> Cost-Control-Test-1-Pass-case
  • Verify the following
  • Plan
  • Cost Estimate
  • Policy Check: Policy check should pass
  • Finally, Disacrd the Run

Step-05-03: Fail Case: Queue Plan and Verify Cost Control Policies Applied

  • Go to Organization (hcta-demo1) -> Workspace(terraform-cloud-demo1) -> Variables
  • Update instance_type Variable 
    # Before Change
instance_type = t3.micro

# After Change
instance_type = t3.2xlarge
  • Queue Plan -> Cost-Control-Test-1-Fail-case
  • Verify the following
  • Plan
  • Cost Estimate
  • Policy Check: Policy check should fail
  • Finally, Disacrd the Run
  • Roll back instance_type to t3.micro

Step-06: Sentinel Policies - Conclusion

  • We can create multiple sentinel policies in different folder paths in single github repository like terraform-sentinel-policies
  • We can apply few of them at Terraform Organization level and few of them at Terraform Workspace level.
  • Very flexible and conveniet.

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