IaC Cost estimation in your PR

Terracotta AI helps DevOps and platform engineers understand the cost implications of proposed infrastructure changes in a pull request. When terraform plan is available (i.e., credentials are configured), Terracotta analyzes resource additions, size changes, and drift re-creations to estimate monthly and annual cost impact.

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Note: There is no tc:cost command at this time, cost analysis is automatically included when triggered by a plan file or review context that changes resource footprint.

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💵 When Cost Analysis Runs

Terracotta supports in-depth, scenario-based cost estimation when asked directly in a PR comment. This includes projections such as:

• 12-month cost forecasts
• Total cost across multiple added resources
• Comparisons between instance types or configurations

Example prompt: @try-terracotta in this diff, what is the cost impact of my changes and what would it look like 12 months out.

Cost analysis is included in PR reviews when:

• A plan file is generated during tc:plan or initial PR indexing
• Resources are added, deleted, or resized
• Drift correction may lead to temporary cost overlap (e.g., re-creating EC2 instances)

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📊 What the Report Contains

1. Summary Table: Cost Estimates (Dynamic Based on Question)

Terracotta analyzes the plan and calculates deltas for new and modified resources:

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🧠 AI Comment Content

The AI-generated cost comment includes:

• Breakdown of new vs existing resources
• Dynamic estimates (monthly by default, 12-month if asked)
• Identification of transient overlaps (e.g., during create-before-destroy)
• Warnings about public exposure risks tied to cost (e.g., unused public instances)
• Optional savings recommendations (e.g., consider t3.micro instead of t2.micro)

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🧮 How Estimates Are Calculated

Terracotta calculates costs based on usage assumptions and region inferred from your Terraform configuration:

• Region: inferred from provider config (e.g., us-west-2)
• Runtime: 730 hours/month
• Pricing model: On-Demand only (for now)

If pricing data is unavailable:

“Pricing data is not available for this usage type or region.”

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💡 Cost Optimization Tips

Terracotta may suggest:

• Replacing instance types (e.g. t2.micro → t3.micro, t4g.micro)
• Adding lifecycle policies to reduce drift-driven billing overlap
• Removing unused public resources
• Consolidating underutilized volumes

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📋 TL;DR

• Cost analysis is automatic, no tc:cost command needed
• Estimates monthly and annual deltas from proposed changes
• Detects overlap risks and offers optimization guidance
• Output is included in the same PR comment as security, drift, and best-practice findings