terraform. Failed to parse ssh private key: ssh: this private key is passphrase protected

When working with Terraform and managing SSH keys, encountering the error message "Failed to parse ssh private key: ssh: this private key is passphrase protected" is a common hurdle. This error typically arises when Terraform attempts to utilize a private SSH key that is encrypted with a passphrase. In this guide, we will explore the reasons for this issue and provide effective solutions to manage SSH keys in Terraform.

Understanding the Error

The error occurs because Terraform cannot load the private key unless it can decrypt it using the passphrase. This can lead to failed deployments or configurations, particularly when automated systems or CI/CD pipelines are involved, as they may not be able to input the passphrase interactively.

Solutions to Resolve the Error

1. Use an SSH Agent

One of the most effective methods is to use an SSH agent, which can hold your decrypted key in memory. Here’s how to set it up:

1. Start the SSH Agent: Open your terminal and start the SSH agent:

   eval $(ssh-agent -s)
   

2. Add Your Key: Use ssh-add to add your private key, which will prompt you for the passphrase:

   ssh-add ~/.ssh/id_rsa
   

3. Update Terraform Provider Configuration: In your Terraform configuration, use the agent parameter to indicate that Terraform should use the SSH agent:

   connection {
     type        = "ssh"
     host        = var.host
     user        = var.user
     private_key = file("~/.ssh/id_rsa")
     agent       = true  # Enable this line
   }
   

2. Remove the Passphrase from the Key

If security policies allow it, you can remove the passphrase from your private key. While this can make key management simpler, it’s essential to consider the security implications:

1. Backup Your Key: Always keep a backup of your private key before making changes.

2. Remove the Passphrase: Use ssh-keygen as follows:

   ssh-keygen -p -f ~/.ssh/id_rsa
   

   You will be prompted to enter the existing passphrase and then leave the new passphrase empty.

3. Generate a New Key Without a Passphrase

If you don't need the additional layer of security provided by a passphrase, consider generating a new SSH key without one:

1. Create a New Key: Use the following command to generate a new SSH key:

   ssh-keygen -t rsa -b 4096 -N '' -f ~/.ssh/id_rsa_new
   

   This creates a new key without a passphrase.

2. Update Your Terraform Configuration: Update your Terraform configuration to use the new key:

   connection {
     type        = "ssh"
     host        = var.host
     user        = var.user
     private_key = file("~/.ssh/id_rsa_new")
   }
   

4. Check Terraform Provider Documentation

If the above methods do not resolve the issue, consult the specific documentation for the Terraform provider you are using. For instance, certain cloud providers may have unique requirements for SSH key management.

Conclusion

Encountering the "Failed to parse ssh private key: ssh: this private key is passphrase protected" error in Terraform can be frustrating, but by understanding the interaction between SSH keys and Terraform, you can implement appropriate solutions. Whether you opt to use an SSH agent, remove the passphrase, or generate a new key, these strategies will help streamline your workflow and improve your deployment processes.

For further troubleshooting, you can refer to communities like Stack Overflow and GitHub discussions such as this issue, which delve into similar issues faced by other users.