Methods to write If/Else Statements in Terraform

If/Else statements are conditional statements that carry out selections based mostly on some identified state, or variable.

Terraform permits you to carry out these if/else statements utilizing a ternary operation which have turn into widespread as short-form if/else statements in lots of programming languages.

The place a language would write one thing much like:

let truthy = false
if (one thing == "worth") {
  truthy = true
} else {
  truthy = false
}

The ternary various could be:

let truthy = one thing == "worth" ? true : false

Or much more simplified:

let truthy = one thing == "worth"

If/Else in Terraform – Utilizing a Ternary

As Terraform solely offers the choice of utilizing a ternary, the next might be used:

vpc_config {
  subnet_ids = (var.env == "dev") ? [data.aws_subnets.devsubnets.ids[0]] : [data.aws_subnets.prodsubnets.ids[0]]
}

You may make it extra readable by breaking it into a number of traces.

Notice that so as to add a multiline ternary, you have to wrap the assertion in brackets (...)

vpc_config {
  subnet_ids = (
    (var.env == "dev") ?
    [data.aws_subnets.devsubnets.ids[0]] :
    [data.aws_subnets.prodsubnets.ids[0]]
  )
}

Including a number of If/Else statements in a single block

The above works nicely when you have a single conditional, however should you want a number of conditionals, then you will have to do the next:

vpc_config {
  subnet_ids = (
    (var.env == "dev") ?
      [data.aws_subnets.devsubnets.ids[0]] :
    (var.env == "uat" ?
      [data.aws_subnets.uatsubnets.ids[0]] :
      [data.aws_subnets.prodsubnets.ids[0]]
    )
  )
}