Output values after apply in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Output value of a computed resource attribute

Given the Terraform configuration below, what will be the output value of instance_ip after applying?

Terraform

resource "aws_instance" "example" {
  ami           = "ami-12345678"
  instance_type = "t2.micro"

  tags = {
    Name = "example-instance"
  }
}

output "instance_ip" {
  value = aws_instance.example.public_ip
}

A "The public IP address of the instance, e.g., 54.123.45.67"

B "The AMI ID used, e.g., ami-12345678"

C "The instance type, e.g., t2.micro"

D "An empty string because public_ip is not set"

💡 Hint

The output references the public_ip attribute of the aws_instance resource.

The output value references aws_instance.example.public_ip, which is the public IP address assigned to the instance after creation.

❓ Configuration

intermediate

Output value from a map variable

What will be the output of region_name after applying this Terraform configuration?

Terraform

variable "regions" {
  type = map(string)
  default = {
    us_east_1 = "US East (N. Virginia)"
    eu_west_1 = "EU (Ireland)"
  }
}

output "region_name" {
  value = var.regions["eu_west_1"]
}

A "eu_west_1"

B "EU (Ireland)"

C "US East (N. Virginia)"

D "null"

💡 Hint

The output accesses the map variable with key "eu_west_1".

The output value is the string mapped to the key "eu_west_1" in the variable regions, which is "EU (Ireland)".

❓ Architecture

advanced

Output value of a list of resource IDs

After applying the following Terraform code, what will be the output value of subnet_ids?

Terraform

resource "aws_subnet" "example" {
  count = 3
  vpc_id     = "vpc-123456"
  cidr_block = "10.0.${count.index}.0/24"
}

output "subnet_ids" {
  value = aws_subnet.example[*].id
}

A ["subnet-abc123", "subnet-def456", "subnet-ghi789"]

B ["10.0.0.0/24", "10.0.1.0/24", "10.0.2.0/24"]

C "subnet-abc123"

D null

💡 Hint

The output uses the splat operator to collect all subnet IDs.

The output collects the id attribute from all three aws_subnet resources into a list of subnet IDs.

❓ security

advanced

Outputting sensitive values

Consider this Terraform output configuration. What will happen after apply?

Terraform

variable "db_password" {
  type      = string
  sensitive = true
}

output "database_password" {
  value     = var.db_password
  sensitive = true
}

A The password will be shown in the output after apply.

B The password will be printed in plain text in the Terraform state file only.

C The password will be hidden in the output and not shown in the CLI.

D Terraform will raise an error because sensitive outputs are not allowed.

💡 Hint

Sensitive outputs are designed to hide values in CLI output.

Marking an output as sensitive hides its value from CLI output but still stores it encrypted in the state file.

✅ Best Practice

expert

Output value referencing a resource attribute that may not exist

What will be the output value of bucket_arn after applying this Terraform configuration if the resource aws_s3_bucket.example is conditionally created with count = 0?

Terraform

resource "aws_s3_bucket" "example" {
  count = 0
  bucket = "my-example-bucket"
}

output "bucket_arn" {
  value = aws_s3_bucket.example[0].arn
}

A "" (empty string)

B null

C The ARN string of the bucket, e.g., arn:aws:s3:::my-example-bucket

D A runtime error because the resource does not exist

💡 Hint

Accessing an index of a resource with count=0 causes an error.

Since the resource count is zero, the list aws_s3_bucket.example is empty. Accessing index 0 causes a runtime error.

Practice

1. What is the main purpose of output values in a Terraform configuration?

easy

A. To create new cloud resources

B. To display important information after Terraform applies changes

C. To define variables used inside Terraform modules

D. To store Terraform state files remotely

Solution

1. Step 1: Understand the role of output values

   Output values are used to show key information after Terraform finishes applying infrastructure changes.

2. Step 2: Differentiate outputs from other Terraform features

   Variables define inputs, resources create infrastructure, and state files store deployment state. Outputs specifically display results.

3. Final Answer:

   To display important information after Terraform applies changes -> Option B

4. Quick Check:

   Outputs = display info after apply [OK]

Hint: Outputs show info after apply, not inputs or resources [OK]

Common Mistakes:

• Confusing outputs with variables
• Thinking outputs create resources
• Mixing outputs with state storage

2. Which of the following is the correct syntax to define an output named instance_ip in Terraform?

easy

A. output "instance_ip" { value = aws_instance.example.private_ip }

B. output instance_ip = aws_instance.example.private_ip

C. output "instance_ip" = aws_instance.example.private_ip

D. output { instance_ip = aws_instance.example.private_ip }

Solution

1. Step 1: Recall Terraform output block syntax

   Outputs use the block syntax: output "name" { value = ... }.

2. Step 2: Match syntax to options

   output "instance_ip" { value = aws_instance.example.private_ip } matches the correct block syntax with quotes and value assignment.

3. Final Answer:

   output "instance_ip" { value = aws_instance.example.private_ip } -> Option A

4. Quick Check:

   Output block = output "name" { value = ... } [OK]

Hint: Outputs need block syntax with quotes and value key [OK]

Common Mistakes:

• Missing quotes around output name
• Using equals sign outside block
• Incorrect block structure

3. Given this Terraform output block:

output "bucket_name" {
  value = aws_s3_bucket.my_bucket.id
}

What will Terraform display after terraform apply if the bucket ID is my-bucket-123?

medium

A. "aws_s3_bucket.my_bucket.id"

B. "my-bucket-123"

C. bucket_name = "my-bucket-123"

D. No output will be shown

Solution

1. Step 1: Understand output display format

   Terraform outputs show the output name followed by an equals sign and the value.

2. Step 2: Apply the known value

   The value aws_s3_bucket.my_bucket.id is "my-bucket-123", so output shows: bucket_name = "my-bucket-123".

3. Final Answer:

   bucket_name = "my-bucket-123" -> Option C

4. Quick Check:

   Output format = name = value [OK]

Hint: Outputs show name = value after apply [OK]

Common Mistakes:

• Expecting only the value without name
• Confusing resource attribute with output text
• Thinking outputs are hidden by default

4. You wrote this output block:

output "db_password" {
  value = var.db_password
  sensitive = true
}

After terraform apply, you still see the password printed in the console. What is the likely cause?

medium

A. You ran terraform output -raw db_password after apply

B. You must set sensitive = false to hide output

C. Terraform does not support sensitive outputs

D. The output block syntax is invalid

Solution

1. Step 1: Understand sensitive output behavior

   Sensitive outputs hide values in the terraform apply console and standard terraform output. However, terraform output -raw <name> bypasses this and shows the value.

2. Step 2: Identify cause of exposure

   The likely cause is running terraform output -raw db_password, which reveals sensitive values.

3. Final Answer:

   You ran terraform output -raw db_password after apply -> Option A

4. Quick Check:

   Sensitive hides output unless -raw [OK]

Hint: Sensitive hides output unless -raw used [OK]

Common Mistakes:

• Thinking sensitive = false hides output
• Believing Terraform can't mark outputs sensitive
• Assuming syntax error causes exposure

5. You want to output a list of instance IPs from multiple AWS instances created with a count. Which output block correctly returns all private IPs after apply?

resource "aws_instance" "web" {
  count = 3
  private_ip = "10.0.0.${count.index + 1}"
}

output "instance_ips" {
  value = ???
}

hard

A. aws_instance.web[0].private_ip

B. aws_instance.web.*

C. aws_instance.web.private_ip

D. [for i in aws_instance.web : i.private_ip]

Solution

1. Step 1: Understand how to access multiple instances' attributes

   When using count, aws_instance.web is a list of resources. To get all private_ip values, use a for expression to extract each.

2. Step 2: Evaluate options for correct syntax

   [for i in aws_instance.web : i.private_ip] uses a for expression to collect private_ip from each instance, which is valid and recommended.

3. Final Answer:

   [for i in aws_instance.web : i.private_ip] -> Option D

4. Quick Check:

   Use for expression to list attributes from count resources [OK]

Hint: Use for expressions to output lists from multiple resources [OK]

Common Mistakes:

• Using wildcard (*) syntax without the attribute
• Accessing single instance only
• Trying to output resource without indexing