In this short article, we will take a look at the Terraform if statement (hint, it doesn’t exist) and look at a few examples. Let’s dive in!
If you are used to traditional programming languages such as C#, Python, Java, etc., you’ll be familiar with the concept of if / else statements. Terraform has no if or else statement but instead uses ternary conditional operators.
What is the conditional structure of Terraform?
The syntax of a conditional expression is as follows:
condition ? true_val : false_valA conditional expression uses the value of a boolean expression to select one of two values. This expression evaluates to true_val if the value of condition is true, and otherwise, to false_val. This is the equivalent of an If-statement.
This logic is particularly useful when fed into the Terraform count statement to deploy multiple of resources. In Terraform, deploying 0 resources is also fine if the condition is not met.
Read more about conditional expressions in Terraform.
To check if a variable is null, run:
variable "null_value" {
type = string
default = null
}
locals {
is_null = var.null_value == null ? true : false
}
output "is_null" {
value = local.is_null
}
Apply complete! Resources: 0 added, 0 changed, 0 destroyed.
Outputs:
is_null = trueThe example below will create the null resource if the condition is true, and because two is greater than one, this will be true.
resource "null_resource" "this" {
count = 2 > 1 ? 1 : 0
}For example, the statement below checks if the variable var.server is set to “UbuntuServer”. If it is true, then count = 0 and will be deployed zero times. If it is set to anything else, then count = 1, and the resource will be deployed 1 time.
Note that Terraform does support traditional logical, equality, and comparison operators such as == (equal to) or != (not equal to) && (and), etc. These operators can be added together to make more complex conditionals.
count = var.server == "UbuntuServer" ? 0 : 1Another common use of conditional expressions is to define defaults to replace invalid values. The example below checks if the variable var.server is an empty string. If it is, then the value is “MicrosoftWindowsServer”. If not, then it is the actual value of var.server .
var.server != "" ? var.server : "MicrosoftWindowsServer"When creating a conditional expression, the two result types can be of any type. In the example below, we have an integer of 100 if the condition is true, and a string “UbuntuServer” if the condition is false.
var.server ? 100 : "UbuntuServer"However, this can cause confusion as Terraform will attempt to find a type that they can both convert to and make those conversions automatically if so. In the above case, both can be converted to a String.
To avoid this, writing the condition with a specific conversion function is recommended (see below using the toString function):
var.server ? tostring(100) : "UbuntuServer"In this example, our security list has egress security rules only if each.value.enable_egress is set to true, otherwise, the dynamic block won’t be generated.
resource "oci_core_security_list" "this" {
for_each = var.sl_params
compartment_id = oci_core_virtual_network.this[each.value.vcn_name].compartment_id
vcn_id = oci_core_virtual_network.this[each.value.vcn_name].id
display_name = each.value.display_name
dynamic "egress_security_rules" {
iterator = egress_rules
for_each = each.value.enable_egress ? each.value.egress_rules : []
content {
stateless = egress_rules.value.stateless
protocol = egress_rules.value.protocol
destination = egress_rules.value.destination
}
}
}One way to create an equivalent to the if / else / elseif statement is to use the coalesce function. coalesce takes any number of arguments and returns the first one that isn’t null or an empty string. When using coalesce all of the arguments must be of the same type.
The example below combines checks the value of var.environment for DEV, UIT and PROD, and uses its value to select a region.
locals{
dev = var.environment == "DEV" ? "uksouth" : ""
uit = var.environment == "UIT" ? "ukwest" : ""
prod = var.environment != "PROD" && var.environment != "UIT" ? "useast2" : ""
region = coalesce(local.dev, local.uit, local.prod)
}Read more about Terraform Locals: What Are They, How to Use Them.
Terraform uses conditional expression logic to build If statements. This can be combined with other functions to form more complex expressions.
We encourage you also to explore how Spacelift makes it easy to work with Terraform. If you need any help managing your Terraform infrastructure, building more complex workflows based on Terraform, and managing AWS credentials per run, instead of using a static pair on your local machine, Spacelift is a fantastic tool for this. If you want to learn more, create a free account today or book a demo with one of our engineers.
Note: New versions of Terraform are placed under the BUSL license, but everything created before version 1.5.x stays open-source. OpenTofu is an open-source version of Terraform that expands on Terraform’s existing concepts and offerings. It is a viable alternative to HashiCorp’s Terraform, being forked from Terraform version 1.5.6.
I hope you enjoyed this article!
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