Terraform : Count,count.index,conditional expressions

1.Overview of Count:
The count parameter on resources can simplify configurations and let you scale resources by simply incrementing a number.

Let’s assume, you need to create two EC2 instances. One of the common approaches is to define two separate resource blocks for aws_instance.

resource "aws_instance" "myfirstec2" {
    # Changed AMI id based on the region
    ami = "ami-0721c9af7b9b75114" 
    instance_type = "t2.micro"
}


resource "aws_instance" "mysecondec2" {
    # Changed AMI id based on the region 
    ami = "ami-0721c9af7b9b75114" 
    instance_type = "t2.micro"
}

With the count parameter, we can simply specify the count value and the resource can be scaled accordingly.

resource "aws_instance" "myfirstec2" {
    # Changed AMI id based on the region
    ami           = "ami-0721c9af7b9b75114" 
    instance_type = "t2.micro"
    count         = 2
}

2.Count Index : In resource blocks where the count is set, an additional count object is available in expressions, so you can modify the configuration of each instance.

This object has one attribute:

count.index — The distinct index number (starting with 0) corresponding to this instance.
Some of the challenges with Count Parameter:

With the below code, terraform will create 2 IAM users. But the problem is that all will have the same name.

resource "aws_iam_user" "iam_user"{
    name = "financeuser"
    count = 2
}

count.index allows us to fetch the index of each iteration in the loop.

resource "aws_iam_user" "iam_user" {
    name = "financeuser.${count.index}"
    count = 2
}

3.Conditional Expressions:
A conditional expression uses the value of a bool expression to select one of two values.

Syntax of Conditional expression:

condition ? true_val : false_val

If the condition is true then the result is true_val. If the condition is false then the result is false_val.

Let’s assume that there are two resource blocks as part of terraform configuration.

Depending on the variable value, one of the resource blocks will run.
If the variable is_test is true then dev environment
is_test is false then prod environment

#Conditional.tf

provider "aws" {
  region     = "us-west-2"
  access_key = "YOUR-ACCESS-KEY"
  secret_key = "YOUR-SECRET-KEY"
}

variable "istest" {}

resource "aws_instance" "dev" {
   ami = "ami-082b5a644766e0e6f"
   instance_type = "t2.micro"
   count = var.istest == true ? 3 : 0
}

resource "aws_instance" "prod" {
   ami = "ami-082b5a644766e0e6f"
   instance_type = "t2.large"
   count = var.istest == false ? 1 : 0
}
    Terraform.tfvars

istest =true

#terraform.tfvars
istest =true

Conclusion:
Discussed about data types and variables, variable files in terraform.

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