terraform/website/docs/configuration/expressions/conditionals.html.md

layout	page_title
language	Conditional Expressions - Configuration Language

Conditional Expressions

A conditional expression uses the value of a bool expression to select one of two values.

The syntax of a conditional expression is as follows:

condition ? true_val : false_val

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

A common use of conditional expressions is to define defaults to replace invalid values:

var.a != "" ? var.a : "default-a"

If var.a is an empty string then the result is "default-a", but otherwise it is the actual value of var.a.

Conditions

The condition can be any expression that resolves to a boolean value. This will usually be an expression that uses the equality, comparison, or logical operators.

Result Types

The two result values may be of any type, but they must both be of the same type so that Terraform can determine what type the whole conditional expression will return without knowing the condition value.