Terraform CLI

Plan

plan will read the terraform HCL file and determine the desired state of the infrastructure, and compare that to the current infra.

• Once this "diff" is determined, terraform plan presents a description of the changes necessary to achieve that desired state (it does not actually make any changes).

If we want, we can save the plan as a runnable artifact that can be fed into the terraform apply command.

The purpose of the plan is to validate configuration changes and confirm that the resulting actions are as expected.

Flags

• -out <filename> - specify an output file for the diff

Markers in the plan diff

• + parts that will be added
• - parts that will be deleted
• ~ parts that will be updated in place (ie. it won't delete and recreate)
• -/+ destroy-then-create
  • this erases the state and results in downtime. We can overcome this downtime by using a resource lifecycle

Apply

apply will perform a plan just like terraform plan command, but then it will actually carry out the planned changes to each resource using the infrastructure provder's API (e.g. AWS API).

• therefore, it can be thought of as "committing" the plan.

Destroy

destroy behaves exactly like deleting every resource from the configuration and then running an apply, except that it doesn't require editing the configuration

• Therefore, this is more convenient if you intend to provision similar resources at a later date.

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import

The import command is how we get Terraform to begin managing a resource that wasn't created in Terraform.

• What's happpening is that Terraform is fetching its data, then including it as part of its state.

terraform import <resource_type>.<resource_identifier> <value>

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Backlinks

• Terraform