terraform-course

Terraform Workflow

This chapter covers the commands used by terraform to dictate the flow of work in a terraform project.

Terraform Init terraform init

Running terraform init is used to initialize your terraform project inside the directory for which it is run. Generally, you will run this command when beginning a new project using terraform. Also, if you modify or change dependencies you will need to run it again to apply the updates. It does the following:

- Download plugin dependencies (Providers, Modules)
- Create a `.terraform` directory
- Create a dependency lock file to enforce expected versions for plugins and
terraform itself
- If supported by your backend, locks your state to prevent writes for all
operations that could write state

Running terraform init with the -upgrade flag will upgrade all plugins to the latest version accounting for their version constraints

Running terraform init with the -get-plugins-false flag will skip plugin installation

Running terraform init with the -plugin-dir=PATH flag will install plugins only from the given directory PATH

Running terraform init with the -lockfile=MODE flag lets you set the mode on the dependency lockfile

terraform get

The terraform get command may be used if you are developing your own terraform module, in this case, you may not need to initialize state or pull new provider binaries.

Writing and Modifying Terraform Code

Terraform has a set of “utility” commands which you can use when developing your terraform project.

terraform fmt

This command may be run to rewrite your configuration files to a standard format and style. Similar to running go fmt or npx prettier --write ., it can be used to format your terraform code.

The command will only format files in the directory that it is called in, if you have subdirectories containing other configuration files, use the -recursive flag to format the files in them as well.

terraform fmt -recursive

To preview the changes being made by the command use the --diff flag:

terraform fmt --diff

terraform validate

This command may be run to validate the syntax and arguments of the configuration files in your Terraform project. Running terraform plan or terraform apply includes a step that runs terraform validate.

terraform console

This command may be run to create an interactive shell for testing expressions that you’d like to include in your configuration files.

Terraform Plan terraform plan

Running terraform plan is done to generate the “Execution Plan” that will be used to create resources, which consists of:

- Reading the current state of any pre-existing remote objects to make sure
that the state is up-to-date
- Comparing the current configuration to the prior state an noting any differences
- Proposing a set of change actions that should, if applied, make the remote
object match the configuration

The command does not carry out the proposed changes, the is done only by terraform apply

There are two types of plans which Terraform will work with:

• Speculative Plan
  • Created with terraform apply
  • Terraform outputs the description of the plan without any intention of running it
• Saved Plan
  • Create with terraform apply -out=FILE
  • This will generate a plan file which can then be passed to terraform apply [FILE]. When using a saved plan, it will not prompt you to confirm and will act like auto-approve

Terraform Apply terraform apply

Running terraform apply is done to execution the actions proposed in an Execution Plan and, ter it runs in two modes.

• Automatic Plan Mode
  • Run terraform apply
  • Executes plan, validate, and the apply
  • Requires users to manually approve the plan by writing “yes”, unless -auto-approve flag is passed
• Saved Plan Mode
  • Running terraform apply FILE
  • Performs exactly the steps specified by the plan file and does not prompt for approval. If you’d like to preview changes you can run terraform show

Commands

Usage: terraform [global options] <subcommand> [args]

The available commands for execution are listed below.
The primary workflow commands are given first, followed by
less common or more advanced commands.

Main commands:
  init          Prepare your working directory for other commands
  validate      Check whether the configuration is valid
  plan          Show changes required by the current configuration
  apply         Create or update infrastructure
  destroy       Destroy previously-created infrastructure