managing-infracost

name	managing-infracost
description	Use when working with Infracost — infracost Terraform cost estimation and FinOps policy enforcement. Covers cost breakdown by resource, diff analysis between plan changes, CI/CD integration checks, policy validation, and cost forecasting. Use when estimating infrastructure cost impact, reviewing Terraform changes, or enforcing cost guardrails.
connection_type	infracost
preload	false

Infracost Management Skill

Estimate and manage Terraform infrastructure costs with Infracost.

MANDATORY: Discovery-First Pattern

Always verify Infracost installation and configuration before running estimates.

Phase 1: Discovery

#!/bin/bash

echo "=== Infracost Version ==="
infracost --version 2>/dev/null

echo ""
echo "=== Configuration ==="
infracost configure get api_key 2>/dev/null && echo "API key: configured" || echo "API key: NOT configured"
infracost configure get pricing_api_endpoint 2>/dev/null
infracost configure get currency 2>/dev/null || echo "Currency: USD (default)"

echo ""
echo "=== Terraform Project Detection ==="
find . -name "*.tf" -maxdepth 3 -exec dirname {} \; | sort -u | head -20

Core Helper Functions

#!/bin/bash

infracost_breakdown() {
    local path="${1:-.}"
    local format="${2:-json}"
    infracost breakdown --path "$path" --format "$format" 2>/dev/null
}

infracost_diff() {
    local path="${1:-.}"
    local compare="${2:-}"
    if [ -n "$compare" ]; then
        infracost diff --path "$path" --compare-to "$compare" --format json 2>/dev/null
    else
        infracost diff --path "$path" --format json 2>/dev/null
    fi
}

Output Rules

• TOKEN EFFICIENCY: Target ≤50 lines per output
• Use --format json with jq for structured extraction
• Round monthly costs to 2 decimal places

Common Operations

Cost Breakdown by Resource

#!/bin/bash
TF_PATH="${1:-.}"

echo "=== Infrastructure Cost Breakdown ==="
infracost breakdown --path "$TF_PATH" --format json 2>/dev/null | jq -r '
    .projects[0].breakdown.resources[] |
    "\(.name)\t$\(.monthlyCost // "0.00")/mo\t\(.resourceType)"
' | sort -t'$' -k2 -rn | column -t | head -25

echo ""
echo "=== Total Monthly Cost ==="
infracost breakdown --path "$TF_PATH" --format json 2>/dev/null | jq '{
    totalMonthlyCost: .totalMonthlyCost,
    totalHourlyCost: .totalHourlyCost,
    resourceCount: (.projects[0].breakdown.resources | length),
    currency: .currency
}'

Diff Analysis (Plan Cost Impact)

#!/bin/bash
TF_PATH="${1:-.}"
BASELINE="${2:-infracost-base.json}"

echo "=== Cost Diff Analysis ==="
if [ -f "$BASELINE" ]; then
    infracost diff --path "$TF_PATH" --compare-to "$BASELINE" --format json 2>/dev/null | jq '{
        totalMonthlyCostBefore: .projects[0].diff.totalMonthlyCost,
        totalMonthlyCostAfter: .totalMonthlyCost,
        diffTotalMonthlyCost: .diffTotalMonthlyCost,
        summary: .summary
    }'
else
    echo "No baseline found. Generating baseline..."
    infracost breakdown --path "$TF_PATH" --format json --out-file "$BASELINE" 2>/dev/null
    echo "Baseline saved to $BASELINE. Run again after making changes."
fi

echo ""
echo "=== Changed Resources ==="
infracost diff --path "$TF_PATH" --compare-to "$BASELINE" --format json 2>/dev/null | jq -r '
    .projects[0].diff.resources[]? |
    select(.diff != null) |
    "\(.name)\tBefore: $\(.monthlyCostBefore // "0")\tAfter: $\(.monthlyCostAfter // "0")\tDiff: $\(.diff.totalMonthlyCost // "0")"
' | column -t | head -15

Policy Check (Cost Guardrails)

#!/bin/bash
TF_PATH="${1:-.}"
POLICY_FILE="${2:-infracost-policy.rego}"

echo "=== Cost Policy Evaluation ==="
if [ -f "$POLICY_FILE" ]; then
    infracost breakdown --path "$TF_PATH" --format json 2>/dev/null \
        | infracost comment --format json --policy-path "$POLICY_FILE" --dry-run 2>/dev/null
else
    echo "No policy file found. Running basic cost checks..."
    RESULT=$(infracost breakdown --path "$TF_PATH" --format json 2>/dev/null)
    TOTAL=$(echo "$RESULT" | jq -r '.totalMonthlyCost // "0"')
    echo "Total monthly cost: \$$TOTAL"
    echo ""
    echo "=== Expensive Resources (>$100/mo) ==="
    echo "$RESULT" | jq -r '
        .projects[].breakdown.resources[] |
        select((.monthlyCost // "0" | tonumber) > 100) |
        "\(.name)\t$\(.monthlyCost)/mo\t\(.resourceType)"
    ' | sort -t'$' -k2 -rn | column -t | head -15
fi

CI Integration Output

#!/bin/bash
TF_PATH="${1:-.}"

echo "=== Generating CI Comment ==="
infracost breakdown --path "$TF_PATH" --format json --out-file /tmp/infracost-report.json 2>/dev/null

echo ""
echo "=== Cost Summary for PR ==="
jq '{
    total_monthly: .totalMonthlyCost,
    total_hourly: .totalHourlyCost,
    projects: [.projects[] | {
        name: .metadata.path,
        monthly_cost: .breakdown.totalMonthlyCost,
        resource_count: (.breakdown.resources | length)
    }]
}' /tmp/infracost-report.json

echo ""
echo "=== Top 5 Costliest Resources ==="
jq -r '.projects[].breakdown.resources[] |
    "\(.name)\t$\(.monthlyCost // "0")/mo"
' /tmp/infracost-report.json | sort -t'$' -k2 -rn | head -5

Multi-Project Cost Report

#!/bin/bash
CONFIG_FILE="${1:-infracost.yml}"

echo "=== Multi-Project Cost Report ==="
if [ -f "$CONFIG_FILE" ]; then
    infracost breakdown --config-file "$CONFIG_FILE" --format json 2>/dev/null | jq -r '
        .projects[] | "\(.metadata.path)\t$\(.breakdown.totalMonthlyCost // "0")/mo\tResources: \(.breakdown.resources | length)"
    ' | column -t
else
    echo "No config file found. Scanning subdirectories..."
    for dir in $(find . -name "*.tf" -maxdepth 3 -exec dirname {} \; | sort -u); do
        COST=$(infracost breakdown --path "$dir" --format json 2>/dev/null | jq -r '.totalMonthlyCost // "0"')
        echo "$dir: \$$COST/mo"
    done | head -15
fi

Safety Rules

• Read-only tool: Infracost only estimates costs -- it never modifies infrastructure
• API key protection: Never log or expose the Infracost API key in CI outputs
• Baseline management: Always generate a baseline before comparing diffs
• Plan file usage: Prefer using Terraform plan files for accuracy over HCL parsing

Output Format

Present results as a structured report:

Managing Infracost Report
═════════════════════════
Resources discovered: [count]

Resource       Status    Key Metric    Issues
──────────────────────────────────────────────
[name]         [ok/warn] [value]       [findings]

Summary: [total] resources | [ok] healthy | [warn] warnings | [crit] critical
Action Items: [list of prioritized findings]

Target ≤50 lines of output. Use tables for multi-resource comparisons.

Anti-Hallucination Rules

1. NEVER assume resource names — always discover via CLI/API in Phase 1 before referencing in Phase 2.
2. NEVER fabricate metric names or dimensions — verify against the service documentation or --help output.
3. NEVER mix CLI commands between service versions — confirm which version/API you are targeting.
4. ALWAYS use the discovery → verify → analyze chain — every resource referenced must have been discovered first.
5. ALWAYS handle empty results gracefully — an empty response is valid data, not an error to retry.

Counter-Rationalizations

Shortcut	Counter	Why
"I'll skip discovery and check known resources"	Always run Phase 1 discovery first	Resource names change, new resources appear — assumed names cause errors
"The user only asked for a quick check"	Follow the full discovery → analysis flow	Quick checks miss critical issues; structured analysis catches silent failures
"Default configuration is probably fine"	Audit configuration explicitly	Defaults often leave logging, security, and optimization features disabled
"Metrics aren't needed for this"	Always check relevant metrics when available	API/CLI responses show current state; metrics reveal trends and intermittent issues
"I don't have access to that"	Try the command and report the actual error	Assumed permission failures prevent useful investigation; actual errors are informative

Common Pitfalls

• Usage-based costs: Resources like data transfer, API calls, and storage I/O cannot be estimated without usage data
• Free tier: Infracost does not account for free tier allowances -- estimates may be higher than actual
• Module support: Nested modules require --path to point to root module
• State vs plan: Breakdown from HCL may differ from plan-based estimates -- plan is more accurate
• Currency: Default is USD -- set infracost configure set currency EUR for other currencies
• Provider pricing: Prices are based on on-demand rates -- reserved/spot pricing requires usage file