How to Use Terraform Plan: Syntax, Example, and Tips

Use the terraform plan command to preview changes Terraform will make to your infrastructure without applying them. It shows a detailed execution plan so you can verify changes before running terraform apply.

Syntax

The basic syntax of terraform plan is simple and can include optional flags to customize the output.

• terraform plan: Shows the execution plan for the current configuration.
• -out=filename: Saves the plan to a file for later use with terraform apply.
• -var 'key=value': Sets a variable value for the plan.
• -input=false: Disables interactive input during the plan.

bash

terraform plan [options]

# Common options:
# -out=planfile.tfplan
# -var 'key=value'
# -input=false

Example

This example shows how to run terraform plan on a simple AWS EC2 instance configuration. It previews the creation of the instance without making any changes.

hcl

provider "aws" {
  region = "us-east-1"
}

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
}

# Run terraform init first to initialize
# Then run terraform plan to see the changes

Output

An execution plan has been generated and is shown below.
Resource actions are indicated with the following symbols:
  + create

Terraform will perform the following actions:

  # aws_instance.example will be created
  + resource "aws_instance" "example" {
      + ami           = "ami-0c55b159cbfafe1f0"
      + instance_type = "t2.micro"
      + id            = (known after apply)
    }

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

Common Pitfalls

Common mistakes when using terraform plan include:

• Not running terraform init before planning, causing errors.
• Forgetting to save the plan with -out when you want to apply the exact plan later.
• Ignoring variable values, leading to unexpected plans.
• Running terraform plan in the wrong directory without configuration files.

bash

Wrong way:
terraform plan

# If you want to apply the exact plan later, do this:
terraform plan -out=myplan.tfplan
terraform apply myplan.tfplan

Quick Reference

Here is a quick summary of useful terraform plan options:

Option	Description
terraform plan	Show the execution plan for current config
-out=filename	Save the plan to a file for later apply
-var 'key=value'	Set or override variable values
-input=false	Disable interactive input during plan
-refresh=true/false	Control state refresh before planning

Key Takeaways

Always run terraform plan to preview changes before applying.

Use -out option to save the plan for exact apply later.

Run terraform init first to initialize your working directory.

Check variable values carefully to avoid unexpected changes.

Run terraform plan in the directory with your Terraform files.