Demo Migrating existing Terraform configuration to OpenTofu

In this guide, you’ll learn how to migrate an existing Terraform project to OpenTofu, verify the changes, and then roll back to Terraform. We’ll cover:

• Applying the initial Terraform configuration
• Installing OpenTofu
• Backing up state files
• Initializing and planning with OpenTofu
• Updating resources and applying changes
• Rolling back to Terraform

1. Apply the Initial Terraform Configuration

1. Navigate to your project directory and review main.tf:

   resource "local_file" "file" {
     filename = "terraform.txt"
     content  = "This file has been created with Terraform"
   }
   

2. Initialize and apply:

   cd ~/opentofu-projects/migration
   terraform init
   terraform apply
   

3. When prompted, enter yes. You should see:

   local_file.file: Creating...
   local_file.file: Creation complete after 0s [id=342bd3c96f4da9100a6360378942400b96bfb5]
   Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
   

4. Verify that terraform.txt exists with the correct content.

2. Install OpenTofu

Refer to the OpenTofu installation guide and select the installer for your OS.

Automated Debian/Ubuntu Installer

curl --proto '=https' --tlsv1.2 -fsSL https://get.opentofu.org/install-opentofu.sh -o install-opentofu.sh
chmod +x install-opentofu.sh
./install-opentofu.sh --install-method deb
rm install-opentofu.sh

Or bundle the commands in install.sh:

#!/bin/bash
curl --proto '=https' --tlsv1.2 -fsSL https://get.opentofu.org/install-opentofu.sh -o install-opentofu.sh
chmod +x install-opentofu.sh
./install-opentofu.sh --install-method deb
rm install-opentofu.sh

Then run:

chmod +x install.sh
./install.sh

Verify the installation:

tofu version

3. Backup the Terraform State

tar czf terraform.tfstate.tar.gz terraform.tfstate

Confirm the archive:

ls
# install.sh  main.tf  terraform.tfstate  terraform.tfstate.tar.gz

4. Initialize with OpenTofu

Switch to the OpenTofu workflow:

tofu init

5. Preview the OpenTofu Plan

Compare the two workflows with this quick reference:

Run the plan:

tofu plan

You should see the same local_file.file resource with filename = "terraform.txt".

6. Update the main.tf for OpenTofu

Change main.tf to point to a new file and content:

resource "local_file" "file" {
  filename = "opentofu.txt"
  content  = "This file has been created with OpenTofu"
}

Validate the updated configuration:

tofu validate

7. Apply with OpenTofu

Apply the OpenTofu configuration:

tofu apply

Type yes when prompted.

Confirm that opentofu.txt has been created with the new content.

8. Roll Back to Terraform

1. Backup the OpenTofu state:

   tar czf terraform.tfstate.tar.gz terraform.tfstate
   

2. Re-initialize with Terraform:

   terraform init
   

   

3. Revert main.tf to the original Terraform resource:

   resource "local_file" "file" {
     filename = "terraform.txt"
     content  = "This file has been created with Terraform"
   }
   

4. Apply with Terraform:

   terraform apply
   

   Enter yes and observe:

   Plan: 1 to add, 0 to change, 1 to destroy.
   Enter a value: yes
   local_file.file: Destroying... [id=91b198b8059c5f72782d9c1d1fe18f6d]
   local_file.file: Destruction complete after 0s
   local_file.file: Creating...
   local_file.file: Creation complete after 0s [id=342bd3c9e4fda9100a36097894200e96b]
   Apply complete! Resources: 1 added, 0 changed, 1 destroyed.
   

You’ve now successfully migrated to OpenTofu and rolled back to Terraform!

Links and References

• Terraform Documentation
• OpenTofu Getting Started
• Terraform local_file Resource