Infracost Terraform Cost Estimation

terraform plan shows what changes. It does not show what those changes cost. Infracost fills that gap by estimating monthly costs from your Terraform code before you apply.

Quick Start

bash

# Install
brew install infracost

# Register for free API key
infracost auth login

# Run cost estimate
cd terraform/
infracost breakdown --path .

Name                                     Monthly Qty  Unit         Monthly Cost
aws_instance.web
├─ Instance usage (t3.large)                     730  hours              $60.74
├─ root_block_device
│  └─ Storage (gp3)                               50  GB                 $4.00
└─ ebs_block_device[0]
   └─ Storage (gp3)                              200  GB                $16.00

aws_rds_db_instance.main
├─ Database instance (db.r6g.large)              730  hours             $131.40
├─ Storage (gp3)                                 100  GB                 $11.50
└─ Additional backup storage                      50  GB                 $0.95

aws_lb.main
├─ Application load balancer                     730  hours              $16.43
└─ Load balancer capacity units                    5  LCU               $36.50

OVERALL TOTAL                                                          $277.52

Diff on Pull Requests

bash

# Compare current branch vs main
infracost diff --path . --compare-to main

Monthly cost will increase by $180.00 (65%)

+ aws_instance.web
  + Instance changed from t3.medium to t3.xlarge     +$60.00
  + Storage increased from 50GB to 200GB              +$12.00

+ aws_rds_db_instance.main (new)
  + Database instance (db.r6g.large)                 +$131.40

~ aws_lb.main
  No cost change

Previous monthly cost: $277.52
New monthly cost:      $457.52

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GitHub Actions Integration

yaml

jobs:
  infracost:
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write
    steps:
      - uses: actions/checkout@v4

      - name: Setup Infracost
        uses: infracost/actions/setup@v3
        with:
          api-key: ${{ secrets.INFRACOST_API_KEY }}

      - name: Generate cost estimate
        run: |
          infracost breakdown --path terraform/ \
            --format json --out-file /tmp/infracost.json

      - name: Post PR comment
        uses: infracost/actions/comment@v3
        with:
          path: /tmp/infracost.json
          behavior: update

The PR comment shows:

markdown

## 💰 Infracost Cost Estimate

| Project | Previous | New | Diff |
|---------|----------|-----|------|
| terraform/production | $277/mo | $457/mo | +$180 (+65%) |

### Changed Resources
| Resource | Previous | New | Diff |
|----------|----------|-----|------|
| aws_instance.web | $65/mo | $125/mo | +$60 |
| aws_rds_db_instance.main | $0 | $132/mo | +$132 |

Cost Policies

Set guardrails in CI:

yaml

# infracost.yml
version: 0.1
projects:
  - path: terraform/
    usage_file: infracost-usage.yml

policies:
  - name: monthly-cost-limit
    description: "Total monthly cost must stay under $5,000"
    resource_type: "*"
    condition:
      totalMonthlyCost: { lt: 5000 }

bash

# Fail CI if cost exceeds threshold
infracost breakdown --path . --format json | \
  jq -e '.totalMonthlyCost | tonumber < 5000' || exit 1

Usage Estimates

Some costs depend on usage (data transfer, API calls):

yaml

# infracost-usage.yml
version: 0.1
resource_usage:
  aws_lambda_function.api:
    monthly_requests: 1000000
    request_duration_ms: 200

  aws_s3_bucket.data:
    monthly_storage_gb: 500
    monthly_get_requests: 100000
    monthly_put_requests: 10000

  aws_nat_gateway.main:
    monthly_data_processed_gb: 100

Without usage estimates, Infracost shows $0 for usage-based resources. Add estimates for realistic projections.

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Multi-Project

bash

# Estimate across all Terraform roots
infracost breakdown \
  --path terraform/vpc \
  --path terraform/eks \
  --path terraform/rds \
  --format table

Supported Providers

Provider	Resources
AWS	250+ resource types
Azure	150+ resource types
GCP	100+ resource types

Covers EC2, RDS, EKS, Lambda, S3, CloudFront, ALB, NAT Gateway, and most commonly used services.

Infracost vs Manual Estimation

Manual cost estimation is error-prone: - Forgot data transfer costs - Wrong instance pricing tier - Missed storage costs - Did not account for multi-AZ

Infracost reads your Terraform directly. If the code says multi_az = true, Infracost doubles the RDS cost. No human estimation errors.

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Luca Berton

Docker Captain, IT automation expert, Red Hat Summit & KubeCon speaker. Building hands-on education for DevOps engineers at CopyPasteLearn.

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Infracost Terraform Cost Estimation

Quick Start

Diff on Pull Requests

Master this topic with hands-on labs

GitHub Actions Integration

Cost Policies

Usage Estimates

Get weekly IT automation tips

Multi-Project

Supported Providers

Infracost vs Manual Estimation

Ready to learn by doing?

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