What Is Terraform Destroy?

With the current pace of infrastructure management, tearing down resources as efficiently as you build them is crucial. Terraform, the open source infrastructure-as-code (IaC) tool from HashiCorp, empowers you to do just that. But what happens when you no longer need that development environment or test cluster? This is where Terraform destroy comes in. If misused, it can lead to unexpected consequences.

In this article, we’ll explore the terraform destroy command, guiding you through its purpose, execution, and best practices to ensure your infrastructure teardown is safe, efficient, and avoids costly mistakes.

What Is Terraform Destroy?

Terraform destroy is a powerful command that systematically dismantles all the infrastructure resources defined within your Terraform configuration files. Its role in the Terraform workflow is to enable users to safely and efficiently decommission infrastructure when it's no longer required. This command ensures a clean and controlled teardown process with several advantages, such as:

• Dependency management: Terraform destroy intelligently analyses the relationships between your resources, deleting them in the correct order to avoid conflicts or orphaned resources (resources left behind with no dependencies).
• Reduced costs: Decommissioning unused resources can significantly reduce your cloud infrastructure spending. Every virtual machine, storage bucket, or database instance that's not actively in use results in unnecessary charges. Terraform destroy helps you eliminate these "ghost" resources and keep your cloud bill under control.
• Improved efficiency and organisation: Cleaning up after testing or temporary deployments often involves manually deleting resources across different cloud platforms. This can be tedious and error-prone. Terraform destroy automates this process, ensuring all resources are removed efficiently and consistently.
• Reduced risk of human error: Manual infrastructure teardown is vulnerable to human mistakes. Accidentally deleting the wrong resource or missing a critical component can lead to outages and downtime. Terraform destroy eliminates this risk by automating the process based on your defined configuration.

Preparing for and Executing Terraform Destroy

Before executing terraform destroy, you must ensure that the following crucial steps are first completed:

• Back up Terraform state files: Terraform state files (.tfstate) hold the current state of your infrastructure managed by Terraform. These files are essential for rebuilding your infrastructure if necessary. Always create a backup of your Terraform state file using a simple command like cp terraform.tfstate terraform.tfstate.backup before running terraform destroy. This allows you to recover your infrastructure if the destroy process encounters unexpected issues.
• Verify access permissions: Ensure you possess the required permissions to delete the resources managed by your Terraform configuration. Insufficient permissions will prevent terraform destroy from executing successfully.
• Update Terraform version: It is recommended that you use the latest stable version of Terraform. Outdated versions may have bugs or compatibility issues that can lead to unexpected behavior during the destroy process. 
• Verify backend configuration: If you're using a remote Terraform state backend (e.g., storing your state file in a cloud storage bucket), ensure it's properly configured and accessible.

The following is the step-by-step procedure before you execute terraform destroy:

• Backup Terraform state file:

$ cp terraform.tfstate terraform.tfstate.backup

• Initialize Terraform directory:

  $ terraform init

This command initializes the Terraform working directory, ensuring all necessary plugins are downloaded and configured correctly.

• Review Terraform plan:

$ terraform plan

While not strictly mandatory, running terraform plan before executing destroy is highly recommended. This command provides a detailed preview of the actions Terraform will take during the destroy process. Reviewing the plan allows you to verify that Terraform identifies the intended resources for deletion and to identify any potential issues before actual destruction occurs.

Handling Common Issues during Terraform Destroy

Encountering issues during the Terraform configuration destruction process is not uncommon. Here are some common pitfalls and how to address them:

• Resource dependencies: Terraform respects dependencies between resources when destroying them. If resource A depends on resource B (e.g., a web application relying on a database), Terraform will attempt to destroy B first. If the destroy command encounters an issue deleting resource B, the destruction of resource A will also fail.
  
  Ensure your Terraform configuration accurately reflects the dependencies between resources. Double-check the order of resource definitions and consider using the depends_on meta-argument to explicitly define dependencies.
  

• Permission errors: Insufficient permissions to delete resources can cause failures. Error: You might see messages indicating "permission denied" or similar access-related errors.
  
  The first step in troubleshooting is scrutinizing the Terraform logs for specific error messages. These messages often provide valuable clues about the root cause of the issue. You can access the logs by running terraform destroy and observing the terminal output. Verify that you have the permission to perform the destroy action.

• State file issues: Corrupted or missing state files can lead to errors. The state files track the current state of your infrastructure managed by Terraform. Messages mentioning "invalid state" or "state not found" could indicate state file issues.
  
  If you suspect a corrupted state file, attempt to restore it from a backup. If a backup is unavailable, consider using Terraform's state locking and unlocking mechanisms to recover from a corrupted state.

• Limited destroy scope: While terraform destroy by default destroys all managed resources, consider using the -target option for more control. This allows you to destroy specific resources within your configuration, potentially mitigating dependency issues.
• Unexpected changes: If you've made manual changes to your infrastructure outside of Terraform (e.g., deleting resources directly through the cloud provider console), your Terraform state file might become out of sync. Running terraform refresh before destroy can help Terraform detect these discrepancies and potentially prevent errors during the destroy process.

Best Practices for Terraform Destroy

Terraform destroy is a powerful tool, but like any powerful tool, it's crucial to wield it effectively. Here are key best practices to ensure your infrastructure teardown is smooth, efficient, and minimizes risks:

• Review plans thoroughly: Always leverage the terraform plan -destroy command before executing the actual destroy process. This command meticulously outlines the actions Terraform will take, allowing you to identify potential issues like dependency conflicts or unintended resource deletion. Treat the plan output as a blueprint and scrutinize it before taking action.

• Automate cleanups with CI/CD integration: For environments with frequent deployments or teardowns, integrate terraform destroy into your CI/CD pipeline. This automates the infrastructure destruction process, streamlining workflows and reducing manual intervention.

• Embrace modular infrastructure: Breaking down your infrastructure into reusable Terraform modules offers several advantages during destruction. Modules promote code organisation and allow you to target specific modules for destruction using the -target option.

• Incremental destroy with -target: For complex infrastructure deployments, consider a staged destruction approach using the -target option. This allows you to destroy resources incrementally, mitigating the risk of accidentally removing critical components. Start by destroying less critical resources and work your way up, carefully monitoring the process at each stage.

• State file management: Regularly back up your Terraform state files and store them securely. These files hold the blueprint of your infrastructure and are vital for recovery in case of accidental destruction or errors. 

• Environment segmentation: Segment your infrastructure into distinct environments (e.g., development, staging, production). This practice limits the impact of a terraform destroy command to a specific environment, preventing accidental destruction of critical production resources.

• Test destroy process in isolated environments: If feasible, consider establishing a dedicated test environment that mirrors your production setup. This allows you to test the terraform destroy process in a controlled setting before executing it in production.

Conclusion

Terraform destroy is a powerful tool for managing the lifecycle of your infrastructure. By understanding its role, preparing adequately, and following best practices, you can use Terraform destroy effectively to manage and clean up your resources. Proper use of this command can help in cost management, ensure clean environments, and automate decommissioning processes, ultimately leading to more efficient infrastructure management.

Pure Storage solutions like Portworx® and Pure Cloud Block Store™ can enhance your Terraform deployments and provide persistent storage for your cloud-based Terraform deployments. With Terraform destroy, Pure Cloud Block Store can also help to store your state files securely.