Conditional Expressions

Sometimes you need to make decisions in your configuration – for example, create a resource only in production, or choose a different value based on a variable. Terraform provides conditional expressions for this.

Conditional Syntax

The ternary operator: condition ? true_val : false_val

variable "environment" { default = "dev" }

locals {
  instance_type = var.environment == "prod" ? "t3.large" : "t2.micro"
  enable_backup = var.environment == "prod" ? true : false
}

Conditional Resource Creation

Use count with a conditional to decide whether to create a resource.

resource "aws_instance" "bastion" {
  count = var.create_bastion ? 1 : 0
  ami   = "ami-abc123"
  instance_type = "t2.micro"
}

# Then refer to it with element(aws_instance.bastion.*.id, 0) or try()

Using for_each with Conditionals

You can also conditionally add items to a map:

locals {
  extra_tags = var.environment == "prod" ? { Backup = "daily" } : {}
}

Conditional in Variable Default

You can use conditionals inside variable defaults, but they cannot reference other variables. Use locals instead.

Example: Conditional Data Source

data "aws_ami" "ubuntu" {
  count = var.use_custom_ami ? 0 : 1
  most_recent = true
  owners = ["099720109477"]
}

locals {
  ami_id = var.use_custom_ami ? var.custom_ami_id : data.aws_ami.ubuntu[0].id
}

Two Minute Drill

Conditional expression: condition ? true_val : false_val.
Use count = condition ? 1 : 0 to conditionally create a resource.
Conditionals work with variables, locals, and resource attributes.
Combine with for_each and maps for advanced logic.

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Conditional Expressions

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