Optional attributes in objects in Terraform - Mini Project: Build & Apply

Optional attributes in objects

📖 Scenario: You are setting up a Terraform configuration to manage cloud resources. Some resources have optional settings that you want to include only if needed.

🎯 Goal: Build a Terraform variable with an object type that includes optional attributes, then use it in a resource configuration.

📋 What You'll Learn

Create a Terraform variable named server_config with an object type that has required and optional attributes

Add a default value for server_config with only the required attributes set

Write a local value that sets a final configuration object using the variable, including optional attributes only if they are defined

Use the final configuration object in a resource block with the correct attribute references

💡 Why This Matters

🌍 Real World

Cloud infrastructure often requires flexible configurations where some settings are optional. This project shows how to handle optional attributes cleanly in Terraform.

💼 Career

Understanding optional attributes in Terraform objects is essential for cloud engineers and DevOps professionals to write adaptable and maintainable infrastructure code.

1

Define the server_config variable with required and optional attributes

Create a Terraform variable called server_config with an object type that has these attributes: name (string, required), cpu (number, required), and tags (map of strings, optional). Set the default value with name as "web-server" and cpu as 2.

Terraform

# Define the variable server_config with required and optional attributes
# Your code here

Need a hint?

Use optional() to mark the tags attribute as optional in the object type.

2

Create a local value to build the final server configuration

Add a local value called final_config that starts with server_config and adds tags only if server_config.tags is defined.

Terraform

variable "server_config" {
  type = object({
    name = string
    cpu  = number
    tags = optional(map(string))
  })
  default = {
    name = "web-server"
    cpu  = 2
  }
}

# Define local final_config to include tags only if defined
# Your code here

Need a hint?

Use merge() with a conditional expression to add tags only if it exists.

3

Use final_config in a resource block

Create a resource block named cloud_server of type example_server that uses local.final_config.name for the name attribute, local.final_config.cpu for the cpu attribute, and includes local.final_config.tags only if it exists.

Terraform

variable "server_config" {
  type = object({
    name = string
    cpu  = number
    tags = optional(map(string))
  })
  default = {
    name = "web-server"
    cpu  = 2
  }
}

locals {
  final_config = merge(
    {
      name = var.server_config.name
      cpu  = var.server_config.cpu
    },
    var.server_config.tags != null ? { tags = var.server_config.tags } : {}
  )
}

# Create resource example_server.cloud_server using local.final_config
# Your code here

Need a hint?

Use a dynamic block to include tags only if they exist.

4

Add an example override with tags in server_config

Update the default value of the server_config variable to include tags with environment = "production" and owner = "team-a".

Terraform

variable "server_config" {
  type = object({
    name = string
    cpu  = number
    tags = optional(map(string))
  })
  default = {
    name = "web-server"
    cpu  = 2
    # Add tags here
  }
}

# Your code here

Need a hint?

Add the tags map inside the default value with the specified keys and values.