Conditionally Creating Terraform Resources

You can conditionally create a Terraform infrastructure object by combining the ternary operator with the count meta-argument.

The count meta-argument lets you define multiple similar objects using a single block. For example:

resource "aws_instance" "server" {
  count = 4 # create four similar EC2 instances
  ami           = "ami-a1b2c3d4"
  instance_type = "t2.micro"
  tags = {
    Name = "Server ${count.index}"
  }
}

We can therefore define a resource to be create with a count of 0 (don't create the resource at all) or 1 based on some condition. Here's an example of how we'd create some resource only if the variable env is set to "prod".

resource "aws_instance" "server" {
  count = var.env == "prod" ? 1 : 0
  ami           = "ami-a1b2c3d4"
  instance_type = "t2.micro"
}

Further reading: Terraform documentation