KodeKloud Notes

terragrunt plan produces a detailed execution plan that shows exactly which resources Terraform will create, update, or destroy. Reviewing this plan before applying changes helps you:

Validate the intended modifications
Catch configuration errors early
Ensure alignment with stakeholder requirements

Terragrunt enhances Terraform’s native plan command by recursively applying it across your entire configuration hierarchy. This provides a unified, end-to-end view of changes across all modules.

Note

Terragrunt delegates to terraform plan under the hood, orchestrating plans across multiple modules and directories.

The image illustrates a Terragrunt plan process, showing how it generates an execution plan and applies it across a configuration hierarchy, with integration with Terraform.

Key Features of Terragrunt Plan

Feature	Description	Benefit
Hierarchical Planning	Executes `terraform plan` across all Terragrunt modules	Consistent visibility across environments
Parallel Execution	Plans multiple modules concurrently	Significant reduction in planning time
Execution Summaries	Aggregates and summarizes results from each module	Quick, consolidated view of all pending changes

Parallel Planning Across Modules

In a modular project structure, terragrunt plan can run in parallel, speeding up the planning phase by generating multiple execution plans simultaneously.

The image illustrates a "Terragrunt plan" with a central icon connected to two puzzle piece icons, representing parallel execution.

Best Practices for `terragrunt plan`

Always review the complete execution plan before applying changes.
Seek approval from relevant stakeholders to prevent unintended infrastructure modifications.
Use version control to track and audit plan outputs.

The image is a slide titled "Terragrunt plan" with icons and text for "Review plan" and "Seek approval," along with a "Best Practices" button.

Warning

Never run terragrunt apply without first validating the execution plan. Unreviewed plans can lead to unexpected downtime or resource drift.

Example: Planning an AWS VPC Module

Below is a sample Terragrunt configuration that references the official Terraform AWS VPC module. Adjust the name input to fit your naming conventions:

terraform {
  source = "tfr://terraform-aws-modules/vpc/aws//?version=5.8.1"
}

inputs = {
  name = "KodeKloud-VPC"
}

To generate the plan, simply run:

$ terragrunt plan

After Terragrunt prepares the consolidated configuration, you’ll see an execution plan similar to this:

# aws_vpc.this[0] will be created
resource "aws_vpc" "this" {
  + arn                                  = (known after apply)
  + cidr_block                           = "10.0.0.0/16"
  + default_network_acl_id               = (known after apply)
  + default_route_table_id               = (known after apply)
  + default_security_group_id            = (known after apply)
  + dhcp_options_id                      = (known after apply)
  + enable_dns_hostnames                 = true
  + enable_dns_support                   = true
  + enable_network_address_usage_metrics = (known after apply)
  + id                                   = (known after apply)
  + instance_tenancy                     = "default"
  + owner_id                             = (known after apply)
  + tags                                 = {
      + "Name" = "KodeKloud-VPC"
    }
  + tags_all                             = {
      + "Name" = "KodeKloud-VPC"
    }
}

Plan: 4 to add, 0 to change, 0 to destroy.

Changes to Outputs:
  + azs                                  = []
  + cgw_arns                             = []
  + cgw_ids                              = []
  + database_nat_gateway_route_ids       = []
  + database_route_table_association_ids = []
  + database_route_table_ids             = []
  + database_subnet_arns                 = []
  + database_subnets_cidr_blocks         = []

Always inspect the plan output to confirm that resource additions and deletions match your expectations before proceeding to terragrunt apply.

Links and References

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