Inconsistent dependency when i do terraform apply from plan -out=file

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05-10-2024

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Terraform: "Inconsistent Dependency" Errors When Using plan -out=file

Have you ever encountered a dreaded "Inconsistent Dependency" error when applying a Terraform plan from a file? This frustrating issue often arises when you attempt to apply a previously saved plan, only to find that the state has changed in the meantime, causing discrepancies between the plan and the actual infrastructure.

This article will delve into the root of this problem, break down its potential causes, and provide solutions to ensure smooth and consistent Terraform deployments.

Understanding the Scenario

Imagine you've meticulously crafted a Terraform plan, using terraform plan -out=my_plan.tfplan to save it for later execution. However, when you try to apply this plan using terraform apply "my_plan.tfplan", you encounter the dreaded "Inconsistent Dependency" error.

Here's a typical error message:

Error: Inconsistent dependency
The provided plan requires the following resource to be created:
  * google_storage_bucket.my_bucket

But its dependencies require the following resource to be created:
  * google_project_iam_member.my_project_member

This error message indicates that the saved plan expects the google_storage_bucket.my_bucket resource to be created, but its dependencies, like the google_project_iam_member.my_project_member, require creation as well. This inconsistency between the saved plan and the current state of your infrastructure leads to the error.

Why This Happens: Common Causes

• State Changes: This is the most common culprit. Between the time you saved your plan and attempted to apply it, someone or something might have made changes to your infrastructure. These changes could be accidental or intentional, but they alter the state of your resources, creating inconsistencies with the saved plan.

• Dependency Ordering: Terraform plans are designed to be executed in a specific order, ensuring dependencies are met. If a resource has dependencies that aren't reflected in the plan, applying it could lead to conflicts. This can happen when the resource creation order changes between the plan and the actual execution.

• Outdated Modules or Providers: If you're using Terraform modules or providers that have been updated since you created your plan, they may introduce changes in resource dependencies, leading to inconsistencies.

Resolving the "Inconsistent Dependency" Error

Here's a step-by-step approach to resolving the "Inconsistent Dependency" error:

1. Update the State: The most straightforward solution is to update your Terraform state file to reflect the current state of your infrastructure. This can be achieved by running terraform init and then terraform apply. This will ensure that the plan and state are in sync.

2. Replan: After updating your state, run terraform plan again to create a new plan based on the updated state. This will resolve any inconsistencies introduced by state changes.

3. Inspect the Plan: Carefully review the newly generated plan. Look for any changes that might have caused dependencies to shift or new resources to be introduced.

4. Modify Your Code: If the "Inconsistent Dependency" error persists after updating the state and replanning, there might be a problem with your Terraform code. Review the resource dependencies and resource ordering. Ensure that the code accurately reflects the desired infrastructure setup.

5. Update Modules and Providers: If you're using outdated modules or providers, update them to the latest versions. This might resolve inconsistencies arising from changes in dependencies or resource definitions.

6. Consider terraform taint: If a specific resource is causing the inconsistency, consider using terraform taint to mark it for recreation. This forces Terraform to destroy and recreate the resource, ensuring that its dependencies are satisfied.

Best Practices for Avoiding Inconsistent Dependencies

• Keep Your State File Updated: Regularly run terraform apply to ensure that your state file reflects the current state of your infrastructure.

• Use terraform plan -out=... with Caution: Only save plans for situations where you want to apply them later, ensuring that no changes are made to your infrastructure in the meantime.

• Test Your Code: Before applying a plan, thoroughly test it to ensure that it meets all your requirements and dependencies are met correctly.

• Version Control: Use version control systems like Git to track changes to your Terraform code and state file. This allows you to easily revert to previous versions if necessary.

Conclusion

The "Inconsistent Dependency" error in Terraform can be frustrating, but by understanding its causes and applying the solutions outlined above, you can ensure smooth and consistent deployments. Remember to stay vigilant about your state file, carefully review plans, and use best practices to avoid encountering this error in the first place.