Terraform plan for preview - Mini Project: Build & Apply

Terraform plan for preview

📖 Scenario: You are working on a cloud infrastructure project using Terraform. Before applying any changes, you want to preview what Terraform will do to your infrastructure. This helps you avoid mistakes and understand the impact of your changes.

🎯 Goal: Create a Terraform configuration for a simple AWS S3 bucket and run a Terraform plan to preview the changes before applying them.

📋 What You'll Learn

Create a Terraform configuration file with an AWS provider and an S3 bucket resource

Add a variable to configure the bucket name

Write the Terraform plan command to preview the infrastructure changes

Include the output block to show the bucket name after apply

💡 Why This Matters

🌍 Real World

Terraform plan is used daily by cloud engineers to preview infrastructure changes before applying them, preventing mistakes and downtime.

💼 Career

Knowing how to write Terraform configurations and use terraform plan is essential for roles like Cloud Engineer, DevOps Engineer, and Infrastructure Engineer.

1

Create Terraform configuration with AWS provider and S3 bucket

Create a Terraform configuration file with the AWS provider block specifying region = "us-east-1". Then create an aws_s3_bucket resource named my_bucket with the bucket name "my-terraform-bucket-12345".

Terraform

# Your Terraform configuration here

Hint

Start by defining the AWS provider with the region. Then add the S3 bucket resource with the exact bucket name.

2

Add a variable for the bucket name

Add a Terraform variable named bucket_name of type string with the default value "my-terraform-bucket-12345". Then update the aws_s3_bucket.my_bucket resource to use this variable for the bucket name.

Terraform

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

resource "aws_s3_bucket" "my_bucket" {
  bucket = var.bucket_name
}

variable "bucket_name" {
  type    = string
  default = "my-terraform-bucket-12345"
}

# Your code here

Hint

Define the variable block with the exact name and default value. Use var.bucket_name in the bucket resource.

3

Write the Terraform plan command

Write the Terraform command to preview the infrastructure changes without applying them. Use the command terraform plan.

Terraform

# Run the Terraform plan command below
# Your code here

Hint

Use the exact command terraform plan to preview changes.

4

Add output to show the bucket name

Add an output block named bucket_name_output that outputs the value of aws_s3_bucket.my_bucket.bucket.

Terraform

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

resource "aws_s3_bucket" "my_bucket" {
  bucket = var.bucket_name
}

variable "bucket_name" {
  type    = string
  default = "my-terraform-bucket-12345"
}

output "bucket_name_output" {
  value = aws_s3_bucket.my_bucket.bucket
}

# Your code here

Hint

Use an output block with the exact name and value to show the bucket name after apply.

Practice

1. What is the main purpose of the terraform plan command?

easy

A. To destroy all existing infrastructure

B. To apply changes directly to cloud resources

C. To initialize the Terraform working directory

D. To preview changes Terraform will make without applying them

Solution

1. Step 1: Understand the role of terraform plan

   This command shows what changes Terraform will make but does not apply them.

2. Step 2: Compare with other commands

   terraform apply applies changes, terraform destroy removes resources, and terraform init initializes the directory.

3. Final Answer:

   To preview changes Terraform will make without applying them -> Option D

4. Quick Check:

   Preview changes = terraform plan [OK]

Hint: Plan previews changes, apply makes changes [OK]

Common Mistakes:

• Confusing plan with apply
• Thinking plan modifies resources
• Mixing plan with init or destroy

2. Which of the following is the correct syntax to run a Terraform plan with a specific variable file named vars.tfvars?

easy

A. terraform plan --vars-file=vars.tfvars

B. terraform plan --varfile vars.tfvars

C. terraform plan -var-file=vars.tfvars

D. terraform plan -varfile=vars.tfvars

Solution

1. Step 1: Recall correct flag for variable files

   The correct flag is -var-file with a hyphen between var and file.

2. Step 2: Check syntax correctness

   terraform plan -var-file=vars.tfvars uses -var-file=vars.tfvars, which is the official syntax. Other options use incorrect flags.

3. Final Answer:

   terraform plan -var-file=vars.tfvars -> Option C

4. Quick Check:

   Use -var-file=filename for variable files [OK]

Hint: Use -var-file=filename to specify variable files [OK]

Common Mistakes:

• Using --varfile instead of -var-file
• Mixing underscores or missing hyphens
• Using --vars-file which is invalid

3. Given this Terraform plan output snippet:

  # aws_instance.example will be created
  + resource "aws_instance" "example" {
      + ami           = "ami-123456"
      + instance_type = "t2.micro"
    }

What does the plus sign (+) before the resource indicate?

medium

A. The resource will be created

B. The resource will be destroyed

C. The resource will be updated in place

D. The resource is unchanged

Solution

1. Step 1: Understand Terraform plan symbols

   The plus sign (+) means Terraform plans to add or create the resource.

2. Step 2: Differentiate from other symbols

   Minus (-) means destroy, ~ means update, no symbol means unchanged.

3. Final Answer:

   The resource will be created -> Option A

4. Quick Check:

   Plus sign (+) = create resource [OK]

Hint: Plus (+) means create, minus (-) means destroy [OK]

Common Mistakes:

• Confusing + with update or destroy
• Ignoring symbols and guessing
• Assuming no symbol means create

4. You run terraform plan but get this error:

Error: No configuration files found!

What is the most likely cause?

medium

A. You ran the command outside the Terraform configuration directory

B. You forgot to run terraform init first

C. Your Terraform version is outdated

D. Your cloud provider credentials are missing

Solution

1. Step 1: Analyze the error message

   The error says no configuration files found, meaning Terraform can't find .tf files.

2. Step 2: Identify common causes

   This usually happens if you run the command outside the folder containing Terraform files.

3. Final Answer:

   You ran the command outside the Terraform configuration directory -> Option A

4. Quick Check:

   No config files = wrong directory [OK]

Hint: Run plan inside folder with .tf files [OK]

Common Mistakes:

• Assuming init fixes missing files
• Blaming credentials for config file errors
• Ignoring current working directory

5. You want to preview changes only for a specific resource named aws_s3_bucket.mybucket without affecting others. Which command achieves this?

hard

A. terraform plan -only=aws_s3_bucket.mybucket

B. terraform plan -target=aws_s3_bucket.mybucket

C. terraform plan --filter=aws_s3_bucket.mybucket

D. terraform plan -resource=aws_s3_bucket.mybucket

Solution

1. Step 1: Recall how to target specific resources in plan

   The -target flag limits the plan to specified resources.

2. Step 2: Verify correct flag usage

   terraform plan -target=aws_s3_bucket.mybucket uses -target=aws_s3_bucket.mybucket, which is the correct syntax. Other options are invalid flags.

3. Final Answer:

   terraform plan -target=aws_s3_bucket.mybucket -> Option B

4. Quick Check:

   Use -target to preview specific resources [OK]

Hint: Use -target=resource_name to limit plan scope [OK]

Common Mistakes:

• Using non-existent flags like -only or --filter
• Forgetting to specify resource type and name
• Assuming plan always shows all resources