Day-05: Terraform variables in AWS

Why do we need variables ?
To use the specific value repeatedly such as environment, tag names, bucket names etc., instead of writing the same value everywhere we just store them and use when needed which increases reusability in the code.

Variables
Variables are classified into two types

1. Based on purpose
2. Based on Value

Based on Purpose

• Input
• Output
• Local

Based on value

• Primitive --> String, number, bool
• Complex --> list, tuple, set, map, object
• ANY and NULL

Input Variables
variables which are used in the code when needed
Syntax:

variable "variable_name"{

     default = "dev"
     type = string  //this is not mandatory. if you don't mention the type of the variable, the terraform will autodetect and use ANY type
}

# Accessing the Variable
var.variable_name
${} // for concatenation of string

#Example:
Name = "${var.variable_name} - Bucket"

Local variables
variables declared in the locals block and accessed anywhere in the code
Syntax:

locals{
   env = "value"
   bucket_name="value"
}

#Accessing locals
local.local_variable_name

Output Variable
the variable which gives output once the resource has been provisioned and the output variables are generally printed on the console
Syntax:

output "variable_name"{
    value = value // Value of the variable you want as output
    description = "description_about_the_output_variable"
}

Ways to declare variables
we can declare variables in many ways:

1. Using the default
2. Environment variables export TF_VAR_variable_name="variable_value"
3. using terraform.tfvars file variable = "variable_value"
4. using terraform.tfvars.json file (similar to terraform.tfvars file but in json format)
5. *auto.tfvars (or) *.auto.tfvars.json files
6. ANY -var in CLI terraform plan -var="variable=variable_value"
7. ANY -var-file (variable files)

# In variables.tfvars
variable "variable_name"{
   default = "variable_value"
}

# Use this file in command line
terraform plan -var-file=variables.tfvars

Commands

terraform output  #show all outputs
terraform output variable_name      # show the output of specific variable
terraform output -json       #show the outputs in json format

# Clean up 
unset TF_VAR_variable_name

In this way we create variables in different ways.

@piyushsachdeva