Count for multiple instances in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Configuration

intermediate

Count Usage for Multiple Instances

Given the Terraform resource below, how many instances will be created?

Terraform

resource "aws_instance" "example" {
  count         = 3
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

A 0

B 1

C 3

D Depends on the AWS account limits

💡 Hint

The count argument defines how many copies of the resource are created.

The count argument set to 3 means Terraform will create 3 instances of the aws_instance resource.

❓ Architecture

intermediate

Dynamic Count with Variable

If the variable "instance_count" is set to 5, how many instances will this Terraform code create?

Terraform

variable "instance_count" {
  type    = number
  default = 5
}

resource "aws_instance" "example" {
  count         = var.instance_count
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

A 5

B 1

C 0

D Depends on the AWS region

💡 Hint

The count uses the variable value directly.

The count is set to the variable instance_count which is 5, so 5 instances will be created.

❓ service_behavior

advanced

Count with Conditional Expression

What is the number of instances created by this Terraform resource if var.create_instances is false?

Terraform

variable "create_instances" {
  type    = bool
  default = false
}

resource "aws_instance" "example" {
  count         = var.create_instances ? 4 : 0
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

A 4

B Terraform will throw an error

C 1

D 0

💡 Hint

The count uses a conditional expression based on the boolean variable.

Since var.create_instances is false, the count evaluates to 0, so no instances are created.

❓ security

advanced

Count with Sensitive Variable

If the variable "instance_count" is marked sensitive and set to 2, how many instances will Terraform create?

Terraform

variable "instance_count" {
  type      = number
  sensitive = true
  default   = 2
}

resource "aws_instance" "example" {
  count         = var.instance_count
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

A 2

B 1

C Terraform will not create any instances because the variable is sensitive

D Terraform will throw a sensitive variable error

💡 Hint

Sensitive variables hide values in logs but do not affect resource creation.

Sensitive variables only hide their values in output and logs; they do not affect the count behavior. Terraform creates 2 instances.

✅ Best Practice

expert

Count with Complex Expression

What is the count value and number of instances created by this resource if var.env is "prod"?

Terraform

variable "env" {
  type    = string
  default = "prod"
}

resource "aws_instance" "example" {
  count = var.env == "prod" ? 5 : 2
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

A count = 2, creates 2 instances

B count = 5, creates 5 instances

C count = 0, creates 0 instances

D Terraform throws an error due to invalid count expression

💡 Hint

The count uses a conditional expression comparing the environment variable.

Since var.env is "prod", the count expression evaluates to 5, so Terraform creates 5 instances.

Practice

1. What does the count argument do in a Terraform resource block?

easy

A. It deletes resources after creation.

B. It creates multiple copies of the resource based on the count value.

C. It renames the resource dynamically.

D. It pauses resource creation until manually resumed.

Solution

1. Step 1: Understand the purpose of count

   The count argument tells Terraform how many copies of a resource to create.

2. Step 2: Recognize the effect of count value

   If count is set to 3, Terraform creates 3 identical resources.

3. Final Answer:

   It creates multiple copies of the resource based on the count value. -> Option B

4. Quick Check:

   count creates copies = A [OK]

Hint: Count controls how many resource copies are made [OK]

Common Mistakes:

• Thinking count deletes resources
• Assuming count renames resources
• Believing count pauses creation

2. Which of the following is the correct syntax to create 4 instances of an AWS EC2 resource using count?

easy

A. resource "aws_instance" "example" { count = 4 }

B. resource "aws_instance" "example" { count = "four" }

C. resource "aws_instance" "example" { count = true }

D. resource "aws_instance" "example" { count = 1..4 }

Solution

1. Step 1: Check the count value type

   The count argument must be a number, not a string or boolean.

2. Step 2: Validate syntax correctness

   resource "aws_instance" "example" { count = 4 } uses count = 4, which is a valid number and correct syntax.

3. Final Answer:

   resource "aws_instance" "example" { count = 4 } -> Option A

4. Quick Check:

   count = number syntax = D [OK]

Hint: Count must be a number, not string or boolean [OK]

Common Mistakes:

• Using string instead of number for count
• Using boolean true/false for count
• Trying to use a range expression directly

3. Given this Terraform snippet:

resource "aws_s3_bucket" "bucket" {
  count = 3
  bucket = "my-bucket-${count.index}"
}

What will be the names of the created buckets?

medium

A. ["my-bucket", "my-bucket", "my-bucket"]

B. ["my-bucket-1", "my-bucket-2", "my-bucket-3"]

C. ["my-bucket-0", "my-bucket-1", "my-bucket-2"]

D. ["my-bucket-3"]

Solution

1. Step 1: Understand count.index usage

   The count.index starts at 0 and increments by 1 for each instance.

2. Step 2: Apply count.index to bucket names

   With count=3, bucket names become "my-bucket-0", "my-bucket-1", and "my-bucket-2".

3. Final Answer:

   ["my-bucket-0", "my-bucket-1", "my-bucket-2"] -> Option C

4. Quick Check:

   count.index starts at 0 = C [OK]

Hint: count.index starts at zero and increments [OK]

Common Mistakes:

• Starting count.index at 1 instead of 0
• Using same name for all instances
• Assuming only one bucket created

4. Identify the error in this Terraform resource block:

resource "aws_security_group" "sg" {
  count = 2
  name = "sg-${count}"
}

medium

A. Name attribute cannot use interpolation.

B. Missing required provider configuration.

C. Count cannot be used with security groups.

D. Using count instead of count.index in the name.

Solution

1. Step 1: Check usage of count in interpolation

   The variable count is not valid inside strings; count.index should be used.

2. Step 2: Confirm correct interpolation

   Replace "sg-${count}" with "sg-${count.index}" to get unique names.

3. Final Answer:

   Using count instead of count.index in the name. -> Option D

4. Quick Check:

   Use count.index for indexes in strings = A [OK]

Hint: Use count.index, not count, inside strings [OK]

Common Mistakes:

• Using count instead of count.index
• Assuming count cannot be used with this resource
• Thinking name interpolation is disallowed

5. You want to create multiple AWS EC2 instances with different instance types using count. Which approach correctly assigns instance types from a list?

hard

A. Use count with var.instance_types[count.index] to assign types.

B. Use count and assign a single instance type to all instances.

C. Use count with a fixed string for instance type.

D. Use count with a random instance type each time.

Solution

1. Step 1: Understand how to assign different values per instance

   Using count.index allows selecting different values from a list for each instance.

2. Step 2: Apply list indexing with count.index

   Accessing var.instance_types[count.index] assigns the correct instance type per resource copy.

3. Final Answer:

   Use count with var.instance_types[count.index] to assign types. -> Option A

4. Quick Check:

   List indexing with count.index assigns unique values = B [OK]

Hint: Index lists with count.index for unique resource values [OK]

Common Mistakes:

• Assigning same instance type to all
• Using fixed string ignoring count.index
• Expecting random assignment without code