Comments in HCL in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the valid single-line comment syntax in HCL

Which of the following lines is a valid single-line comment in HashiCorp Configuration Language (HCL)?

A # This is a comment

B // This is a comment

C /* This is a comment */

D <!-- This is a comment -->

💡 Hint

HCL supports single-line comments starting with # or //, and multi-line comments with /* */.

In HCL, comments can start with # or // for single-line comments, and /* */ for multi-line comments. The syntax <!-- --> is used in HTML, not HCL.

❓ Configuration

intermediate

Effect of comments on resource count

Given the following Terraform configuration snippet, how many resources will be created?

Terraform

resource "aws_instance" "example1" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

# resource "aws_instance" "example2" {
#   ami           = "ami-654321"
#   instance_type = "t2.micro"
# }

// resource "aws_instance" "example3" {
//   ami           = "ami-abcdef"
//   instance_type = "t2.micro"
// }

A 3

B 2

C 0

D 1

💡 Hint

Lines starting with # or // are ignored by Terraform.

Only the first resource block is active. The other two resource blocks are commented out and ignored, so only one resource will be created.

❓ service_behavior

advanced

Multi-line comment effect in HCL

What will happen if you use the following multi-line comment syntax in a Terraform configuration file?

Terraform

/*
resource "aws_s3_bucket" "bucket" {
  bucket = "my-bucket"
  acl    = "private"
}
*/

resource "aws_s3_bucket" "bucket2" {
  bucket = "my-bucket-2"
  acl    = "private"
}

A Only aws_s3_bucket.bucket2 will be created; the first resource is ignored.

B Both aws_s3_bucket.bucket and aws_s3_bucket.bucket2 will be created.

C Terraform will raise a syntax error due to incorrect comment syntax.

D No resources will be created because all are commented out.

💡 Hint

Multi-line comments in HCL start with /* and end with */.

The multi-line comment correctly comments out the first resource block, so only the second resource block is active and created.

❓ security

advanced

Security risk of commented sensitive data

Why is it a bad practice to leave sensitive information like passwords or API keys in commented lines in Terraform files?

A Commented lines are encrypted and safe from exposure.

B Terraform automatically removes comments before applying configurations.

C Commented sensitive data can still be exposed in version control or logs.

D Comments are ignored by all tools and cannot be accessed.

💡 Hint

Think about where your code files are stored and who can see them.

Comments remain in the source files and can be seen by anyone with access to the code repository or logs, risking exposure of sensitive data.

❓ Architecture

expert

Impact of comments on Terraform plan output

Consider a Terraform file where a resource block is commented out using single-line comments. What will be the impact on the output of the `terraform plan` command?

Terraform

resource "aws_security_group" "sg1" {
  name        = "sg1"
  description = "Allow SSH"
  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

// resource "aws_security_group" "sg2" {
//   name        = "sg2"
//   description = "Allow HTTP"
//   ingress {
//     from_port   = 80
//     to_port     = 80
//     protocol    = "tcp"
//     cidr_blocks = ["0.0.0.0/0"]
//   }
// }

A Terraform plan will show changes only for aws_security_group.sg1; sg2 is ignored.

B Terraform plan will show no changes because comments disable all resources.

C Terraform plan will fail with a syntax error due to commented lines.

D Terraform plan will show changes for both sg1 and sg2 resources.

💡 Hint

Comments disable code from being processed by Terraform.

Commented resource blocks are ignored by Terraform, so only the active resource (sg1) will appear in the plan output.