Terraform Error Locking State

I ran into a Terraform Error Locking State error recently after experiencing a temporary loss of network connectivity whilst in the middle of running a terraform plan to deploy some Azure resources. When I tried to re-run the terraform apply command to attempt to deploy the resources again, this is what was returned:

Error: Error locking state: Error acquiring the state lock: state blob is already locked
 Lock Info:
   ID:        a77xxxxxx-cxxc-70f1-xxx-xxxxxxxx
   Path:      terraform-storage/terraform.tfstate
   Operation: OperationTypeApply
   Who:       domain\user@host
   Version:   0.14.5
   Created:   2022-02-21 15:51:13.5132763 +0000 UTC
   Info:

The reason for this is that I had configured the terraform backend to use an Azure storage account to store the terraform state file. When I tried to run the terraform apply command after my network connectivity was restored, the state file had a lock due to my previous failed attempt to run the plan.

When using a backend configuration that supports the functionality, state locking helps safeguard your terraform deployments by ensuring only one user has write access to the state file, which guards against corruption when you have multiple users potentially interacting with and running the terraform plan.

In my case, I knew I was the only user as this was in my own test environment. Therefore I could safely remove the lock. This is done using the terraform force-unlock command. To run this successfully you need to have the ID: from the lock info in the error message. For example:

terraform force-unlock a77xxxxxx-cxxc-70f1-xxx-xxxxxxxx
 Do you really want to force-unlock?
   Terraform will remove the lock on the remote state.
   This will allow local Terraform commands to modify this state, even though it
   may be still be in use. Only 'yes' will be accepted to confirm.

As you can see, you will be prompted to type yes to continue.

Terraform state has been successfully unlocked!
The state has been unlocked, and Terraform commands should now be able to
 obtain a new lock on the remote state.

Once unlocked I was able to run the terraform apply command successfully to deploy my Azure resources.

Use caution when running this in a environment where its possible the state lock was created by another user. The online Terraform documentation states the following:

Be very careful with this command. If you unlock the state when someone else is holding the lock it could cause multiple writers. Force unlock should only be used to unlock your own lock in the situation where automatic unlocking failed.

If you are in any doubt I would suggest waiting for a while before attempting to unlock the state, and/or investigate who may have a valid lock on the state file.