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What does terraform refresh really do?

While using terraform to deploy a fairly large infrastructure in AWS, our remote tfstate got corrupted and was deleted.

From the documentation, I gather that terraform refresh should query AWS to get the real state of the infrastructure and update the tfstate accordigly, but that does not happen: my tfstate is untouched and plan + apply give a lot of Already existing errors.

What does terraform refresh really do?

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Bruno9779 Avatar asked Mar 06 '17 14:03

Bruno9779


People also ask

Does Terraform run Terraform refresh?

Plan-> In the aforementioned scenario when the 2nd EC2 instance is deleted and when you try again with terraform plan it does refresh the terraform state but in-memory prior to plan. The refreshed state will be used to calculate this plan, but will not be persisted in local or remote state storage.

Does Terraform plan refresh state file?

Terraform uses this local state to create plans and make changes to your infrastructure. Prior to any operation, Terraform does a refresh to update the state with the real infrastructure.

How do I turn off Terraform refresh?

The -refresh=false option is used in normal planning mode to skip the default behavior of refreshing Terraform state before checking for configuration changes. CLI: Use terraform plan -refresh=false or terraform apply -refresh=false .

How do you reduce Terraform plan time?

Best practices state that you should split things up to only group stuff that needs to be applied at the same time to minimise blast radius, make it easier to make concurrent changes while not breaking state and reduce the time it takes Terraform to refresh and build the dependency graph.


1 Answers

terraform refresh attempts to find any resources held in the state file and update with any drift that has happened in the provider outside of Terraform since it was last ran.

For example, lets say your state file contains 3 EC2 instances with instance ids of i-abc123, i-abc124, i-abc125 and then you delete i-abc124 outside of Terraform. After running terraform refresh, a plan would show that it needs to create the second instance while a destroy plan would show that it only needs to destroy the first and third instances (and not fail to destroy the missing second instance).

Terraform makes a very specific decision to not interfere with things that aren't being managed by Terraform. That means if the resource doesn't exist in its state file then it absolutely will not touch it in any way. This enables you to run Terraform alongside other tools as well as making manual changes in the AWS console. It also means that you can run Terraform in different contexts simply by providing a different state file to use, allowing you to split your infrastructure up into multiple state files and save yourself from catastrophic state file corruption.

To get yourself out of your current hole I suggest you use terraform import liberally to get things back into your state file or, if possible, manually destroy everything outside of Terraform and start from scratch.

In future I would suggest both splitting out state files to apply for more granular contexts and also to store your remote state in an S3 bucket with versioning enabled. You could also look towards tools like Terragrunt to lock your state file to help avoid corruption or wait for the native state file locking in the upcoming 0.9 release of Terraform.

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ydaetskcoR Avatar answered Nov 07 '22 07:11

ydaetskcoR