Check blocks for assertions in Terraform - Mini Project: Build & Apply

Using Terraform check blocks for assertions

📖 Scenario: You are managing cloud infrastructure with Terraform. You want to ensure that certain conditions are met before applying changes. For example, you want to check that the instance type is allowed and the number of instances is within limits.

🎯 Goal: Create a Terraform configuration that uses check blocks to assert that the instance type is either t2.micro or t2.small, and that the number of instances is between 1 and 3.

📋 What You'll Learn

Create a variable instance_type with default t2.micro

Create a variable instance_count with default 2

Add a check block to assert instance_type is t2.micro or t2.small

Add a check block to assert instance_count is between 1 and 3

💡 Why This Matters

🌍 Real World

Using check blocks helps catch configuration errors early in Terraform plans, avoiding costly mistakes in cloud infrastructure.

💼 Career

Cloud engineers and DevOps professionals use Terraform check blocks to enforce policies and ensure infrastructure meets requirements before deployment.

1

Create variables for instance type and count

Create a variable called instance_type with default value "t2.micro" and a variable called instance_count with default value 2.

Terraform

# Create variable instance_type with default "t2.micro"
# Create variable instance_count with default 2

Need a hint?

Use variable blocks with default values.

2

Add check block for instance_type

Add a check block that asserts the variable instance_type is either "t2.micro" or "t2.small". Use the expression var.instance_type == "t2.micro" || var.instance_type == "t2.small".

Terraform

variable "instance_type" {
  type    = string
  default = "t2.micro"
}

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

# Add check block for instance_type here

Need a hint?

Use a check block with condition and error_message.

3

Add check block for instance_count

Add a check block that asserts the variable instance_count is between 1 and 3 inclusive. Use the expression var.instance_count >= 1 && var.instance_count <= 3.

Terraform

variable "instance_type" {
  type    = string
  default = "t2.micro"
}

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

check "valid_instance_type" {
  condition     = var.instance_type == "t2.micro" || var.instance_type == "t2.small"
  error_message = "Instance type must be 't2.micro' or 't2.small'."
}

# Add check block for instance_count here

Need a hint?

Use a check block with a condition that uses comparison operators.

4

Add resource block using variables

Add an aws_instance resource named example that uses var.instance_type for instance_type and var.instance_count for count.

Terraform

variable "instance_type" {
  type    = string
  default = "t2.micro"
}

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

check "valid_instance_type" {
  condition     = var.instance_type == "t2.micro" || var.instance_type == "t2.small"
  error_message = "Instance type must be 't2.micro' or 't2.small'."
}

check "valid_instance_count" {
  condition     = var.instance_count >= 1 && var.instance_count <= 3
  error_message = "Instance count must be between 1 and 3."
}

# Add aws_instance resource block here

Need a hint?

Use a resource block with count and instance_type set from variables.