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Terraform
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Create a Terraform plan

  • 23min
  • |
  • Terraform

The core Terraform workflow consists of three main steps after you have written your Terraform configuration:

  • Initialize prepares your workspace so Terraform can apply your configuration.
  • Plan allows you to preview the changes Terraform will make before you apply them.
  • Apply makes the changes defined by your plan to create, update, or destroy resources.

When you provision infrastructure, Terraform creates an execution plan before it applies any changes. Terraform creates the plan by comparing your Terraform configuration to the state of your infrastructure. The execution plan consists of a set of changes that create, update, or destroy resources. You can use the terraform plan command to compare your configuration to your resource's state, review changes before you apply them, or to refresh your workspace's state. Terraform plan supports automation workflows in CI/CD pipelines by guaranteeing that the infrastructure changes Terraform applies match the ones you or your team approve, even if the deploy process completes across different machines or at different times.

In this tutorial, you will review how Terraform generates an execution plan, what the plan contains, and the role of the terraform plan command in your Terraform workflow. To do so, you will create and apply a saved Terraform plan, review its contents, and analyze how a plan reflects changes to your configuration. You will also learn how to target specific resources when you create a Terraform plan.

Prerequisites

You can complete this tutorial using the same workflow with either Terraform Community Edition or HCP Terraform. HCP Terraform is a platform that you can use to manage and execute your Terraform projects. It includes features like remote state and execution, structured plan output, workspace resource summaries, and more.

Select the HCP Terraform tab to complete this tutorial using HCP Terraform.

This tutorial assumes that you are familiar with the Terraform workflow. If you are new to Terraform, complete the Get Started tutorials first.

In order to complete this tutorial, you will need the following:

Clone the example repository

In your terminal, clone the learn-terraform-plan repository.

$ git clone https://github.com/hashicorp-education/learn-terraform-plan

Navigate to the cloned repository.

$ cd learn-terraform-plan

Review configuration

The example configuration in this repository creates an EC2 instance through resources and local and public modules. The modules/aws-ec2-instance subdirectory contains the local module used to create the instance.

$ tree
.
├── LICENSE
├── README.md
├── main.tf
├── modules
│   └── aws-ec2-instance
│       ├── main.tf
│       └── variables.tf
├── terraform.tf
└── variables.tf

Terraform uses the provider versions specified in the terraform.tf file.

terraform.tf

terraform {
  required_version = "~> 1.6"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "5.7.0"
    }
    random = {
      source  = "hashicorp/random"
      version = "3.5.1"
    }
  }
## ...
}

Open the top-level main.tf file. This configuration uses the aws provider to create an EC2 instance using an Ubuntu AMI.

main.tf

provider "aws" {
  region = var.region
}

provider "random" {}

data "aws_ami" "ubuntu" {
  most_recent = true

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-bionic-18.04-amd64-server-*"]
  }

  filter {
    name   = "virtualization-type"
    values = ["hvm"]
  }

  owners = ["099720109477"] # Canonical
}

resource "random_pet" "instance" {
  length = 2
}

module "ec2-instance" {
  source = "./modules/aws-ec2-instance"

  ami_id        = data.aws_ami.ubuntu.id
  instance_name = random_pet.instance.id
}

This configuration uses the random_pet resource to generate a name for your instance. The module.ec2-instance block uses the local aws-ec2-instance module to define your instance.

The configuration also passes the random pet name to the hello module, which will generate outputs with the random pet name.

main.tf

module "hello" {
  source  = "joatmon08/hello/random"
  version = "6.0.0"

  hellos = {
    hello        = random_pet.dog.id
    second_hello = "World"
  }

  some_key = "secret"
}

Initialize your configuration

In order to generate your execution plan, Terraform needs to install the providers and modules referenced by your configuration. Then, it will reference them to create your plan.

Initialize the Terraform configuration with terraform init.

$ terraform init
Initializing the backend...
Initializing modules...
- ec2-instance in modules/aws-ec2-instance
Downloading registry.terraform.io/joatmon08/hello/random 6.0.0 for hello...
- hello in .terraform/modules/hello

Initializing provider plugins...
- Reusing previous version of hashicorp/random from the dependency lock file
- Reusing previous version of hashicorp/aws from the dependency lock file
- Installing hashicorp/aws v5.7.0...
- Installed hashicorp/aws v5.7.0 (signed by HashiCorp)
- Installing hashicorp/random v3.5.1...
- Installed hashicorp/random v3.5.1 (signed by HashiCorp)

Terraform has been successfully initialized!

You may now begin working with Terraform. Try running "terraform plan" to see
any changes that are required for your infrastructure. All Terraform commands
should now work.

If you ever set or change modules or backend configuration for Terraform,
rerun this command to reinitialize your working directory. If you forget, other
commands will detect it and remind you to do so if necessary.

Create a plan

There are three commands that tell Terraform to generate an execution plan:

  1. The terraform plan command creates a plan consisting of a set of changes that will make your resources match your configuration. This lets you preview the actions Terraform would take to modify your infrastructure before applying them. Terraform plan does not make any changes to your resources, you must apply a plan for Terraform to make changes.

    You can also save a plan with the -out flag. Later, you can apply the saved plan, and Terraform will only perform the changes listed in the plan. In an automated Terraform pipeline, applying a saved plan file ensures that Terraform only makes the changes you expect, even if your pipeline runs across multiple machines at different times.

  2. The terraform apply command applies a Terraform plan. If you do not pass a saved plan, then Terraform will a create a plan and prompt you for approval before applying the plan.

  3. The terraform destroy command creates an execution plan to delete all of the resources managed by your workspace.

Generate a saved plan with the -out flag. You will review and apply this plan later in this tutorial.

$ terraform plan -out "tfplan"
data.aws_ami.ubuntu: Reading...
data.aws_ami.ubuntu: Read complete after 0s [id=ami-055744c75048d8296]

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # random_pet.instance will be created
  + resource "random_pet" "instance" {
      + id        = (known after apply)
      + length    = 2
      + separator = "-"
    }

  # module.ec2-instance.aws_instance.main will be created
  + resource "aws_instance" "main" {
## ...

Plan: 4 to add, 0 to change, 0 to destroy.

───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

Saved the plan to: tfplan

To perform exactly these actions, run the following command to apply:
    terraform apply "tfplan"

Terraform created a plan and saved it in the tfplan file.

Since you have not yet applied this configuration, Terraform plans to create all of the resources defined in it.

When you create a plan, Terraform checks your workspace for an existing state file. Since you have not yet applied this configuration, your workspace's state is empty, and Terraform plans to create all of the resources defined in your configuration.

You can apply the saved plan file to execute these changes, but the contents of the plan are not in a human-readable format. Use the terraform show command to print out the saved plan.

$ terraform show "tfplan"
Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # random_pet.instance will be created
  + resource "random_pet" "instance" {
      + id        = (known after apply)
      + length    = 2
      + separator = "-"
    }
## ...
  # module.hello.random_pet.server will be created
  + resource "random_pet" "server" {
      + id        = (known after apply)
      + keepers   = {
          + "hello"      = (known after apply)
          + "secret_key" = "secret"
        }
      + length    = 2
      + separator = "-"
    }

Plan: 4 to add, 0 to change, 0 to destroy.

This is the same output that Terraform printed when you created your saved plan. You can review this plan output with your team before you apply the saved plan to ensure that the changes are the ones you expect.

Terraform can also report the contents of the saved plan as JSON. This is often useful when using Terraform in automated pipelines, as you can use code to inspect the plan.

Convert the saved plan into JSON, pass it to jq to format it, and save the output into a new file.

$ terraform show -json "tfplan" | jq > tfplan.json

Warning

Terraform plan files can contain sensitive data. Never commit a plan file to version control, whether as a binary or in JSON format.

Review the plan

In this section, you will review the data Terraform captures about your resources in a plan file. Use the jq command to query the JSON formatted version of your plan.

Terraform records the version of Terraform used to generate the plan, and the version of the plan file format. This will ensure that you use the same version to apply these changes when you use the saved plan.

$ jq '.terraform_version, .format_version' tfplan.json
"1.6.0"
"1.2"

Review plan configuration

The .configuration JSON object is a snapshot of your configuration at the time of the terraform plan.

This configuration snapshot captures the versions of the providers recorded in your .terraform.lock.hcl file, ensuring that you use the same provider versions that generated the plan to apply it. Note that the configuration accounts for both the provider version used by the root module and child modules.

$ jq '.configuration.provider_config' tfplan.json
{
  "aws": {
    "name": "aws",
    "full_name": "registry.terraform.io/hashicorp/aws",
    "version_constraint": "5.7.0",
    "expressions": {
      "region": {
        "references": [
          "var.region"
        ]
      }
    }
  },
  "random": {
    "name": "random",
    "full_name": "registry.terraform.io/hashicorp/random",
    "version_constraint": "3.5.1"
  }
}

The configuration section further organizes your resources defined in your top level root_module.

$ jq '.configuration.root_module.resources' tfplan.json
[
  {
    "address": "random_pet.instance",
    "mode": "managed",
    "type": "random_pet",
    "name": "instance",
    "provider_config_key": "random",
    "expressions": {
      "length": {
        "constant_value": 2
      }
    },
    "schema_version": 0
  },
## ...

The module_calls section contains the details of the modules used, their input variables and outputs, and the resources to create.

$ jq '.configuration.root_module.module_calls' tfplan.json
{
  "ec2-instance": {
    "source": "./modules/aws-ec2-instance",
    "expressions": {
      "ami_id": {
        "references": [
          "data.aws_ami.ubuntu.id",
          "data.aws_ami.ubuntu"
        ]
      },
      "instance_name": {
        "references": [
          "random_pet.instance.id",
          "random_pet.instance"
        ]
      }
    },
## ...

The configuration object also records any references to other resources in a resource's written configuration, which helps Terraform determine the correct order of operations when it applies your plan.

$ jq '.configuration.root_module.module_calls.hello.expressions.hellos.references' tfplan.json
[
  "random_pet.instance.id",
  "random_pet.instance"
]

Review planned resource changes

Review the planned resources changes to the aws_instance resource from the ec2-instance local module.

The representation includes:

  • The action field captures the action taken for this resource, in this case create.
  • The before field captures the resource state prior to the run. In this case, the value is null because the resource does not yet exist.
  • The after field captures the state to define for the resource.
  • The after_unknown field captures the list of values that will be computed or determined through the operation and sets them to true.
  • The before_sensitive and after_sensitive fields capture a list of any values marked sensitive. Terraform will use these lists to determine which output values to redact when you apply your configuration.
$ jq '.resource_changes[] | select( .address == "module.ec2-instance.aws_instance.main")' tfplan.json
{
  "address": "module.ec2-instance.aws_instance.main",
  "module_address": "module.ec2-instance",
  "mode": "managed",
  "type": "aws_instance",
  "name": "main",
  "provider_name": "registry.terraform.io/hashicorp/aws",
  "change": {
    "actions": [
      "create"
    ],
    "before": null,
    "after": {
      "ami": "ami-055744c75048d8296",
      "credit_specification": [],
      "get_password_data": false,
      "hibernation": null,
      "instance_type": "t2.micro",
      "launch_template": [],
      "source_dest_check": true,
      "timeouts": null,
      "user_data_replace_on_change": false,
      "volume_tags": null
    },
    "after_unknown": {
      "arn": true,
      "associate_public_ip_address": true,
      "availability_zone": true,
## ...
    }
  }
}

Review planned values

The planned_values object is a report of the differences between the "before" and "after" values of your resources, showing you the planned outcome for a run that would use this plan file.

In this example, the module.ec2-instance.aws_instance resource includes the address that you will use to reference the resource in your Terraform configuration, the provider name, and the values of all of the attributes as one object. This format resolves the differences between the prior and expected state in one object to demonstrate the planned outcomes for the configuration, which is easier to use for any downstream consumers of the plan data. For example, the Terraform Sentinel CLI tests policies against the planned outcomes recorded here. The cost estimation feature in HCP Terraform also relies on the planned_values data to determine changes to your infrastructure spend.

$ jq '.planned_values' tfplan.json
{
  "root_module": {
    "resources": [
      {
        "address": "random_pet.instance",
## ...
      }
    ],
    "child_modules": [
      {
        "resources": [
          {
            "address": "module.ec2-instance.aws_instance.main",
            "mode": "managed",
            "type": "aws_instance",
            "name": "main",
            "provider_name": "registry.terraform.io/hashicorp/aws",
            "schema_version": 1,
            "values": {
              "ami": "ami-055744c75048d8296",
              "credit_specification": [],
              "get_password_data": false,
## ...

Apply a saved plan

In your terminal, apply your saved plan.

Note

When you apply a saved plan file, Terraform will not prompt you for approval and instead immediately execute the changes. This workflow is primarily used in automation.

$ terraform apply "tfplan"
random_pet.instance: Creating...
random_pet.instance: Creation complete after 0s [id=apt-zebra]
module.hello.random_pet.number_2: Creating...
module.hello.random_pet.server: Creating...
module.hello.random_pet.number_2: Creation complete after 0s [id=sweet-kid]
module.hello.random_pet.server: Creation complete after 0s [id=more-swan]
module.ec2-instance.aws_instance.main: Creating...
module.ec2-instance.aws_instance.main: Still creating... [10s elapsed]
module.ec2-instance.aws_instance.main: Still creating... [20s elapsed]
module.ec2-instance.aws_instance.main: Still creating... [30s elapsed]
module.ec2-instance.aws_instance.main: Creation complete after 32s [id=i-04107c0289b72e9c1]

Apply complete! Resources: 4 added, 0 changed, 0 destroyed.

Terraform applied your changes according to the saved plan.

Modify configuration

Input variables let you easily update configuration values without having to edit your configuration files.

Open the variables.tf file in the top-level configuration directory. Add the configuration below to define a new input variable to use for the hello module.

variables.tf

variable "secret_key" {
  type        = string
  sensitive   = true
  description = "Secret key for hello module"
}

Then, create a terraform.tfvars file, and set the new secret_key input variable value.

terraform.tfvars

secret_key = "TOPSECRET"

Warning

Never commit .tfvars files to version control.

Finally, update the hello module configuration in main.tf to reference the new input variable.

main.tf

module "hello" {
  source  = "joatmon08/hello/random"
  version = "6.0.0"

  hellos = {
    hello        = random_pet.instance.id
    second_hello = "World"
  }

  some_key = var.secret_key
}

Create a new plan

Create a new Terraform plan and save it as tfplan-input-var.

$ terraform plan -out "tfplan-input-var"
random_pet.instance: Refreshing state... [id=apt-zebra]
module.hello.random_pet.number_2: Refreshing state... [id=sweet-kid]
module.hello.random_pet.server: Refreshing state... [id=more-swan]
data.aws_ami.ubuntu: Reading...
data.aws_ami.ubuntu: Read complete after 0s [id=ami-055744c75048d8296]
module.ec2-instance.aws_instance.main: Refreshing state... [id=i-04107c0289b72e9c1]

Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
-/+ destroy and then create replacement

Terraform will perform the following actions:

  # module.hello.random_pet.server must be replaced
-/+ resource "random_pet" "server" {
      ~ id        = "more-swan" -> (known after apply)
      ~ keepers   = { # forces replacement
          # Warning: this attribute value will be marked as sensitive and will not
          # display in UI output after applying this change.
          ~ "secret_key" = (sensitive value)
            # (1 unchanged element hidden)
        }
        # (2 unchanged attributes hidden)
    }

Plan: 1 to add, 0 to change, 1 to destroy.

───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

Saved the plan to: tfplan-input-var

To perform exactly these actions, run the following command to apply:
    terraform apply "tfplan-input-var"

Convert the new plan file into a machine-readable JSON format.

$ terraform show -json tfplan-input-var | jq > tfplan-input-var.json

Review new plan

When you created this plan, Terraform determined that the working directory already contains a state file, and used that state to plan the resource changes.

Since Terraform created this plan with existing resources and using input variables, your plan file has some new fields.

Review plan input variables

Now that you have defined input variables, Terraform captures them in the plan file as well.

$ jq '.variables' tfplan-input-var.json
{
  "project_name": {
    "value": "terraform-plan"
  },
  "region": {
    "value": "us-east-1"
  },
  "secret_key": {
    "value": "TOPSECRET"
  }
}

Warning

Although you marked the input variable as sensitive, Terraform still stores the value in plaintext in the plan file. Since Terraform plan files can contain sensitive information, you should keep them secure and never commit them to version control.

Unlike input variables, Terraform does not record the values of any environment variables used for your configuration in your plan files. Using environment variables is one of the recommended ways to pass sensitive values, such as provider credentials, to Terraform.

Review plan prior_state

When you created this plan, Terraform determined that the working directory already contains a state file, and used that state to plan the resource changes. Unlike the first run's plan file, this file now contains a prior_state object, which captures the state file exactly as it was prior to the plan action.

$ jq '.prior_state' tfplan-input-var.json
{
  "format_version": "1.0",
  "terraform_version": "1.6.0",
  "values": {
    "root_module": {
      "resources": [
        {
          "address": "data.aws_ami.ubuntu",
          "mode": "data",
          "type": "aws_ami",
          "name": "ubuntu",
          "provider_name": "registry.terraform.io/hashicorp/aws",
          "schema_version": 0,
## ...
        }
      ]
    }
  }
}

Review plan resource changes

Now that your state file tracks resources, Terraform will take the existing state into consideration when it creates an execution plan. For example, the module.hello.random_pet.server object now contains data in both the before and after fields, representing the prior and desired configurations respectively.

$ jq '.resource_changes[] | select( .address == "module.hello.random_pet.server")' tfplan-input-var.json
{
  "address": "module.hello.random_pet.server",
  "module_address": "module.hello",
  "mode": "managed",
  "type": "random_pet",
  "name": "server",
  "provider_name": "registry.terraform.io/hashicorp/random",
  "change": {
    "actions": [
      "delete",
      "create"
    ],
    "before": {
      "id": "tidy-crawdad",
  ## ...
    "after": {
      "keepers": {
        "hello": "fun-possum",
        "secret_key": "TOPSECRET"
      },
## ...
  "action_reason": "replace_because_cannot_update"
}

Notice that the actions list is now set to ["delete","create"] and that the action_reason is "replace_because_cannot_update" - the change to the secret_key for the resource is destructive, so Terraform must both delete and create this resource. Terraform determines whether it can update a resource in place or must recreate it based on which provider attributes you changed.

Once you have created resources in the working directory, Terraform uses the prior state, the data returned by a refresh operation, and the written configuration to determine the changes to make. Terraform supports additional flags that you can use to modify how it constructs an execution plan. For example, you can create a plan that only refreshes the state file without modifying resource configuration, or target only specific resources for either update or replacement.

Clean up infrastructure

Now that you have completed this tutorial, destroy the resources created before moving on. Create and apply a destroy plan.

$ terraform plan -destroy -out "tfplan-destroy"
## ...
Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  - destroy

Terraform will perform the following actions:

  # random_pet.instance will be destroyed
  - resource "random_pet" "instance" {
## ...
Plan: 0 to add, 0 to change, 4 to destroy.

───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

Saved the plan to: tfplan-destroy

To perform exactly these actions, run the following command to apply:
    terraform apply "tfplan-destroy"

When you use the -destroy flag, Terraform creates a plan to destroy all of the resources in the configuration. Apply the plan to destroy your resources.

$ terraform apply "tfplan-destroy"
## ...
Terraform used the selected providers to generate the following execution plan.
Resource actions are indicated with the following symbols:
  - destroy

Terraform will perform the following actions:

  # random_pet.instance will be destroyed
  - resource "random_pet" "instance" {
## ...
Plan: 0 to add, 0 to change, 4 to destroy.

Do you really want to destroy all resources?
  Terraform will destroy all your managed infrastructure, as shown above.
  There is no undo. Only 'yes' will be accepted to confirm.

  Enter a value: yes
## ...
Destroy complete! Resources: 4 destroyed.

The terraform destroy command is a shortcut that creates a destroy plan and then waits for you to approve it. Saving a destroy plan allows you to review it before applying, just like a regular saved plan.

Next steps

In this tutorial, you reviewed how Terraform constructs an execution plan and uses saved plans. You also explored the relationship of the terraform plan and terraform apply commands.

Check out the following tutorials to try out some of the available plan modes and options:

Previous

Init

 Next

Apply

This tutorial also appears in:

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