How to Manage SSH Keys in Terraform for Azure VMs Without Resource Recreation

Описание: Learn how to handle SSH key configurations in Terraform for Azure VMs to avoid unnecessary resource recreation and team disruptions.
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This video is based on the question https://stackoverflow.com/q/63413564/ asked by the user 'python-noob' ( https://stackoverflow.com/u/12226869/ ) and on the answer https://stackoverflow.com/a/63446386/ provided by the user 'Charles Xu' ( https://stackoverflow.com/u/9773937/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the SSH Key Issue in Terraform with Azure VMs

If you're working with Terraform to manage Azure resources, you may encounter issues when different team members use their own SSH keys. This can lead to frustrating scenarios where resources, like Virtual Machines (VMs), are destroyed and recreated when configuration changes are made. In this guide, we'll explore the problem and provide the best solutions to ensure a smooth collaborative experience when using Terraform for Azure VMs.

The Problem: SSH Key Mismatches

The main challenge arises when the azurerm_linux_virtual_machine resource configuration incorporates SSH keys. Here’s how the typical setup looks:

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What's Happening?

Dynamic Public Key Loading: The file() function loads the SSH public key from the local machine. If each team member has different SSH keys, Terraform will treat any changes in the public key as a significant alteration to the resources, triggering a recreation of the VM.

Resource Recreation: When one team member runs terraform apply, the Terraform state syncs with the public key from their machine. If another member tries to apply changes, Terraform sees this different public key, leading to the deletion of existing resources and their recreation with the new key.

This results in multiple VMs being destroyed and unnecessarily re-created, causing disruptions in development and operations.

Proposed Solutions: Managing SSH Keys Effectively

To avoid these issues, here are two effective solutions:

1. Use a Static Public Key

Switch from dynamic loading of the public key to a static public key defined directly in your configuration. Here’s how you can modify the code:

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Benefits of Using a Static Key:

Consistency: The public key remains the same regardless of who runs the terraform apply command.

Collaboration: Team members can make changes without worrying about altering resource states due to mismatched SSH keys.

Flexibility: You can still update other configurations like Network Security Group (NSG) rules without impacting the VM's existence.

2. External Secrets Management

For larger teams, consider adopting an external secrets management tool (like HashiCorp Vault or Azure Key Vault) to store and manage SSH keys. This allows you to reference the public key without hardcoding it into your Terraform scripts.

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Conclusion

By implementing either the static public key configuration or leveraging an external secrets management strategy, you can effectively manage SSH keys in Terraform for Azure VMs. This not only provides stability to your infrastructure but also fosters better collaboration among team members without the fear of unintended resource deletion.

Embrace these best practices in your Terraform workflows, and enjoy a more seamless and integrated development experience!