Terraform Source-Swap with Terragrunt

Source-Swap Script

Author: Kermit Smith

Date: December 2024

This script reads terragrunt.hcl and swaps the source in the main.tf file for the module specified in terragrunt.hcl.
This is useful when you want to swap the source of a module in other environments while using same Terraform root module.

Usage

Enter a source-swap block as shown in the examples below. Be sure to comment out the block to avoid Terragrunt errors.
Note: This is not a function of Terragrunt.

source-swap "my-module" {
  old-source = "git::https://github.com/org/repository//module-call"
  new-source = "git::https://github.com/org/repository//module-call?ref=test"
}

source-swap "my-module2" {
  old-source = "git::https://github.com/org/repository//module-call"
  new-source = "git::https://github.com/org/repository//module-call?ref=test"
}

# Wild card * can be used to swap all occurrences of old-source with new-source in main.tf
source-swap "*" {
  old-source = "git::https://github.com/org/repository//module-call"
  new-source = "git::https://github.com/org/repository//module-call?ref=test"
}

Run this script in the same directory where you run Terragrunt.exe.
I run it in the yaml pipeline as follows: (copy depends on where you place it of course. Here I have it my Terragrunt root)

- name: Copy source-swap.sh to current folder
      run: |
        cp ../../../source-swap.sh .
        pwd
        ls -la

- name: Run source-swap.sh to replace module sources if requested in terragrunt.hcl
  run: |
    chmod +x ./source-swap.sh
    ./source-swap.sh