README.md

Terraform Variables

Overriding default Variable values with terraform.tfvars file

Using terraform.tfvars to Override Variable Values

In Terraform, you can customize your Terraform configurations without altering the code by using a terraform.tfvars file.

• terraform.tfvars file allows you to set custom values for your Terraform variables.

• When you run Terraform commands, it automatically reads terraform.tfvars and will auto-load the variables present in this file by overriding the default values in variables.tf

• Name of the file should be exactly terraform.tfvars

• you can also use terraform.tfvars.json Files whose names end with .json are parsed instead as JSON objects, with the root object properties corresponding to variable names

• Syntax

  variable_name = "new_value"

• Example:

  00_provider.tf

  terraform {
  required_providers {
      aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
      }
  }
  }
  
  provider "aws" {
  #region = "us-east-1"
  region = var.aws_region
  
  default_tags {
      tags = {
      Terraform = "yes"
      #Owner = "Venkatesh"
      Owner = var.owner
      }
  }
  }

  01_ec2.tf

  resource "aws_instance" "myec2" {
  # terraform arguments without variables
  # ami = "ami-0df435f331839b2d6"
  # instance_type = "t2.micro"
  # count = 1
  
  # using variables for arguments
  ami           = var.ec2_ami
  instance_type = var.ec2_instance_type
  count         = var.instance_count
  
  tags = {
      Name = "Linux2023"
  }
  }

  02_variables.tf

  variable "aws_region" {
  description = "AWS Region In Which Resources will be Created"
  type        = string
  default     = "us-east-1"
  }
  
  variable "owner" {
  description = "Name of the Engineer who is creating Resources"
  type        = string
  default     = "Venkatesh"
  }
  
  variable "ec2_ami" {
  description = "AWS EC2 AMI Amazon Linux 2023"
  type        = string
  default     = "ami-0df435f331839b2d6" # Amazon Linux 2023
  }
  
  variable "ec2_instance_type" {
  description = "EC2 Instance Type"
  type        = string
  default     = "t2.micro"
  }
  
  variable "instance_count" {
  description = "Number of EC2"
  type        = number
  default     = 1
  }

• In the above example, We've defined five variables:

  1. aws_region: default AWS Region to be used
  2. owner: Name of the Engineer who is creating Resources
  3. ec2_ami: AWS EC2 AMI
  4. ec2_instance_type: AWS EC2 Instance type
  5. instance_count: Number of EC2 to be Created

• Now, Lets create terraform.tfvars file and explore how the file overrides the default variables.

• let's override ec2_instance_type and owner variables in our configuration. Create a terraform.tfvars file like this:

  terraform.tfvars

  ec2_instance_type = "t3.small"
  owner             = "Amar"

• terraform plan Output

  • You can notice the change in ec2_instance_type to t3.small and owner to Amar and

  $ terraform plan
  
  Terraform used the selected providers to generate the following execution plan. Resource actions are indicated with the following symbols:
  + create
  
  Terraform will perform the following actions:
  
  # aws_instance.myec2[0] will be created
  + resource "aws_instance" "myec2" {
      + ami                                  = "ami-0df435f331839b2d6"
      + arn                                  = (known after apply)
      + associate_public_ip_address          = (known after apply)
      + availability_zone                    = (known after apply)
      + cpu_core_count                       = (known after apply)
      + cpu_threads_per_core                 = (known after apply)
      + disable_api_stop                     = (known after apply)
      + disable_api_termination              = (known after apply)
      + ebs_optimized                        = (known after apply)
      + get_password_data                    = false
      + host_id                              = (known after apply)
      + host_resource_group_arn              = (known after apply)
      + iam_instance_profile                 = (known after apply)
      + id                                   = (known after apply)
      + instance_initiated_shutdown_behavior = (known after apply)
      + instance_lifecycle                   = (known after apply)
      + instance_state                       = (known after apply)
      + instance_type                        = "t3.small"
      + ipv6_address_count                   = (known after apply)
      + ipv6_addresses                       = (known after apply)
      + key_name                             = (known after apply)
      + monitoring                           = (known after apply)
      + outpost_arn                          = (known after apply)
      + password_data                        = (known after apply)
      + placement_group                      = (known after apply)
      + placement_partition_number           = (known after apply)
      + primary_network_interface_id         = (known after apply)
      + private_dns                          = (known after apply)
      + private_ip                           = (known after apply)
      + public_dns                           = (known after apply)
      + public_ip                            = (known after apply)
      + secondary_private_ips                = (known after apply)
      + security_groups                      = (known after apply)
      + source_dest_check                    = true
      + spot_instance_request_id             = (known after apply)
      + subnet_id                            = (known after apply)
      + tags                                 = {
          + "Name" = "Linux2023"
          }
      + tags_all                             = {
          + "Name"      = "Linux2023"
          + "Owner"     = "Amar"
          + "Terraform" = "yes"
          }
      + tenancy                              = (known after apply)
      + user_data                            = (known after apply)
      + user_data_base64                     = (known after apply)
      + user_data_replace_on_change          = false
      + vpc_security_group_ids               = (known after apply)
      }
  
  Plan: 1 to add, 0 to change, 0 to destroy.

References :

Variable Definitions (.tfvars) Files