Conditional Provisioning with Ternary Operators

Terraform · 15 min · Practical

Dynamically evaluate infrastructure configurations using Terraform conditional expressions (condition ? true_val : false_val). Automatically toggle EC2 instance sizing based on deployment environment variables like prod vs dev.

Core Implementation Highlights

Environment Input Variablevariable "selectenvironment" { default = "prod" }

Ternary Conditional Logicvar.selectenvironment == "prod" ? "t2.micro" : "t4g.small"

Security Group FirewallSSH (Port 22) Ingress & Open Outbound Egress

Public IP Outputaws_instance.create_instance.public_ip

The Complete Terraform Code

Save the code below into main.tf. It declares the environment input variable, registers an SSH Key Pair, sets up a Security Group firewall, provisions an EC2 instance with conditional instance sizing, and exports the public IP address.

main.tf

# Define environment selection variable (Defaults to "prod")
variable "selectenvironment" {
  type    = string
  default = "prod"
}

# Register SSH Key Pair using local public key
resource "aws_key_pair" "shankey" {
  key_name   = "serverkey"
  public_key = file("/home/ak/.ssh/id_rsa.pub")
}

# Security Group Firewall allowing SSH (Port 22) Ingress
resource "aws_security_group" "webserver_ig" {
  name = "webserver_ig"

  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

# Provision EC2 Instance with Conditional Instance Sizing
resource "aws_instance" "create_instance" {
  ami                         = "ami-0272eca93537d5c9d"
  instance_type               = var.selectenvironment == "prod" ? "t2.micro" : "t4g.small"
  associate_public_ip_address = true
  vpc_security_group_ids      = [aws_security_group.webserver_ig.id]
  key_name                    = aws_key_pair.shankey.key_name
}

# Output the Public IP address of the created instance
output "aws_ec2_name" {
  value = aws_instance.create_instance.public_ip
}

Resource-by-Resource Explanation

variable "selectenvironment"

Defines a configurable input variable that controls the target environment. Setting a default value of "prod" allows the configuration to execute safely without requiring CLI input, but can be overridden at runtime using -var="selectenvironment=dev".

main.tf

variable "selectenvironment" {
  type    = string
  default = "prod"
}

Ternary Operator (condition ? true : false)

The core of conditional logic in HCL uses standard ternary syntax: CONDITION ? TRUE_VAL : FALSE_VAL.

When var.selectenvironment == "prod": Evaluates to true, assigning "t2.micro".
When var.selectenvironment != "prod": Evaluates to false, assigning "t4g.small".

main.tf

resource "aws_instance" "create_instance" {
  ami           = "ami-0272eca93537d5c9d"
  instance_type = var.selectenvironment == "prod" ? "t2.micro" : "t4g.small"
  key_name      = aws_key_pair.shankey.key_name
  vpc_security_group_ids = [aws_security_group.webserver_ig.id]
}

aws_security_group & aws_key_pair

Binds custom network firewall rules and SSH authentication to the server:

aws_key_pair.shankey: Reads local public key file via file("/home/ak/.ssh/id_rsa.pub").
aws_security_group.webserver_ig: Opens port 22 for inbound SSH connections and enables unrestricted egress.

main.tf

resource "aws_key_pair" "shankey" {
  key_name   = "serverkey"
  public_key = file("/home/ak/.ssh/id_rsa.pub")
}

output "aws_ec2_name" {
  value = aws_instance.create_instance.public_ip
}

Deployment & Execution Commands

Test both production and non-production conditional branches using Terraform variable flags:

Terminal

# 1. Initialize AWS Provider
$ terraform init

# 2. Plan for Production (Defaults selectenvironment to "prod" -> t2.micro)
$ terraform plan

# 3. Plan for Staging/Dev (Overrides variable -> t4g.small or t2.small)
$ terraform plan -var="selectenvironment=dev"

# 4. Apply Production Configuration
$ terraform apply -var="selectenvironment=prod" -auto-approve

# 5. Clean up infrastructure when done
$ terraform destroy -auto-approve