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In this lesson, we’ll dive into the terragrunt apply command—your gateway to automating infrastructure changes with Terragrunt and Terraform. After reviewing changes with terragrunt plan, terragrunt apply executes the approved plan, provisioning or updating resources across one or multiple modules.
The image is a diagram explaining the purpose of "Terragrunt apply," showing it initiates the application of configuration and enables users to implement changes.

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Why Run terragrunt apply?

Always execute terragrunt apply after confirming the plan from terragrunt plan. This two-step approach ensures you understand potential changes before they impact your infrastructure.
The image is a diagram titled "Terragrunt apply," showing a workflow with icons and text describing steps for executing and deploying changes safely.
Under the hood, Terragrunt invokes Terraform’s terraform apply command and manages shared configuration across modules for you.
The image is an infographic about "Terragrunt apply," highlighting its ability to perform across multiple modules and enhance deployment speed, with a focus on parallel execution.
By default, Terragrunt will execute modules in parallel, vastly reducing deployment time in large, modular repositories.
The image provides best practices for using Terragrunt, emphasizing reviewing planned changes and seeking approval before applying them. It includes icons and a "Best Practices" label at the bottom.

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Best Practices

  • Review the Plan: Always inspect the execution plan to catch unintended changes.
  • Get Stakeholder Approval: Ensure team members sign off on modifications.
  • Use Version Constraints: Pin module and provider versions for reproducibility.

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Quick Reference: Common terragrunt apply Flags

FlagDescriptionExample
—auto-approveSkip interactive confirmationterragrunt apply --auto-approve
—targetRestrict apply to a specific module or resourceterragrunt apply --target=module.vpc
—terragrunt-include-external-dependenciesInclude external dependencies in apply runterragrunt apply --terragrunt-include-external-dependencies

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Applying Your VPC Module

We’ve already approved the execution plan for our VPC module. Below is the Terragrunt configuration and the commands to apply it: 
terraform {
  source = "tfr://terraform-aws-modules/vpc/aws//?version=5.8.1"
}

inputs = {
  name = "KodeKloud-VPC"
}
Run: 
$ terragrunt apply
Terragrunt will re-display the plan. After confirming the details, type yes: 
Do you want to perform these actions?
Terraform will perform the actions described above.
Only 'yes' will be accepted to approve.

Enter a value: yes
Upon completion, you’ll see: 
Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
Terragrunt then prints the resulting outputs: 
private_nat_gateway_route_ids           = []
private_route_table_association_ids     = []
private_route_table_ids                 = []
private_subnet_arns                     = []
private_subnets                         = []
public_route_table_ids                  = []
public_subnets                          = []
vpc_arn                                 = "arn:aws:ec2:us-east-1:654654587809:vpc/vpc-03218326bbd74f4c"
vpc_cidr_block                          = "10.0.0.0/16"
vpc_enable_dns_hostnames                = true
vpc_id                                  = "vpc-03218326bbd74f4c"
vpc_owner_id                            = "654654587809"

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