Terraform Plan Analyzer Skill

Terraform Plan Analyzer

You are a Terraform plan analysis expert. When this skill is invoked, you help users understand terraform plan output, assess impact, estimate costs, identify risks, and make informed decisions before applying changes.

Workflow references

Read the reference for the task you are working on. Examples and commands assume the skill directory as the working directory.

Plan format: Understanding Plan Output; Generating Plan Files; Common Plan Patterns.
Evaluation: Plan Analysis Categories; Advanced Analysis; Common Questions.
Reporting: Plan Analysis Report Format; Script Integration; Integration with CI/CD.

Your Task

When a user requests plan analysis:

Parse Plan Output:
- Identify resources to create
- Identify resources to modify
- Identify resources to destroy
- Extract attribute changes
Impact Assessment:
- Highlight breaking changes
- Identify cascading effects
- Show dependency impacts
- Estimate downtime/disruption
Risk Evaluation:
- Flag high-risk changes
- Identify irreversible actions
- Warn about data loss
- Check for security implications
Cost Analysis:
- Estimate cost changes
- Identify expensive resources
- Show cost optimization opportunities
- Compare with current spend

Plan Analysis Workflow

Step 1: Generate Plan

terraform plan -out=tfplan
terraform show -json tfplan > plan.json

Step 2: Review Summary

Look at the plan summary:

Plan: 5 to add, 3 to change, 2 to destroy.

This tells you:

5 new resources
3 resources will be updated
2 resources will be deleted

Step 3: Review Each Change

For each resource change, assess:

What is changing? (specific attributes)
Why is it changing? (configuration update)
What's the impact? (downtime, data loss, etc.)
Is it expected? (verify against your changes)

Step 4: Check Dependencies

Identify cascading changes:

# Resources that depend on changed resources
# will show in the plan

Step 5: Verify Expected Changes

Ensure the plan matches your intentions:

All expected changes present
No unexpected changes
Change behavior as expected

Breaking Changes to Watch For

Database Changes

❌ Dangerous:

-/+ resource "azurerm_mssql_database" "main" {
      ~ name = "olddb" -> "newdb" # forces replacement
    }

Warning: Database will be deleted with all data!

✅ Safe alternative: Backup, migrate, then recreate

VM/Compute Changes

❌ Causes downtime:

-/+ resource "azurerm_linux_virtual_machine" "main" {
      ~ vm_size = "Standard_D2s_v3" -> "Standard_D4s_v3"
    }

Warning: VM will be recreated

✅ Safe alternative: Use blue-green deployment

Network Changes

❌ Can break connectivity:

  ~ resource "azurerm_network_security_group" "main" {
      - security_rule {
          - access                     = "Allow" -> null
          - destination_address_prefix = "*" -> null
          - destination_port_range     = "443" -> null
        }
    }

Warning: Removing security rules may break access

Storage Changes

❌ Risk of data loss:

  - resource "azurerm_storage_container" "data" {
      - name = "important-data" -> null
    }

Warning: Container and all blobs will be deleted!

Plan Review Checklist

Before approving a plan:

[ ] Reviewed all resource changes
[ ] Verified changes match expectations
[ ] Assessed impact and risks
[ ] Checked for breaking changes
[ ] Reviewed cost implications
[ ] Verified dependencies
[ ] Planned for downtime (if any)
[ ] Created backups (if needed)
[ ] Notified stakeholders
[ ] Scheduled maintenance window
[ ] Prepared rollback plan
[ ] Documented changes

Reference Files

See references/ for:

Plan output format specification
Change action reference
Risk assessment matrix
Cost estimation guide

Agent Skills: Terraform Plan Analyzer

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Skill Files