How to use "for_each" to iterate over a list in Terraform
In Terraform, the for_each expression allows you to iterate over a list or map and create multiple instances of a resource or module based on the elements of that list or map. This is useful when you want to manage multiple similar resources or configurations in a more dynamic way.
The for_each value must be a map or a set of strings, which creates an instance for each item in that map or set. Each instance has a distinct infrastructure object associated with it, and each is separately created, updated, or destroyed when the configuration is applied.
Using for_each on a list of strings:
provider "null" {}
variable "user_names" {
type = list(string)
default = ["user1", "user2", "user3"]
}
resource "null_resource" "users" {
for_each = toset(var.user_names)
triggers = {
name = each.value
}
}
output "user_names_output" {
value = [for user in null_resource.users : user.triggers.name]
}
Code explanation
Line 1:
This line defines a Terraform provider named
null. Thenullprovider is a built-in provider that does nothing but can be useful in certain scenarios, like generating data or for testing purposes.
Line 3–6:
This block defines a variable named
user_names.The variable has a type of
list(string), meaning it is a list of strings.The default value of the variable is set to
["user1", "user2", "user3"], so if no value is provided when running Terraform, this default list will be used.
Line 8–14:
This block defines a
null_resourcenamedusers.The
for_eachargument is set totoset(var.user_names), which means that this resource will be created for each unique value in theuser_nameslist variable.Inside the
triggersblock, a trigger is set for each instance of thenull_resourceusing the name from each value in theuser_nameslist.
Line 16–18:
This block defines an output named
user_names_output.The value of the output is set using a list comprehension (
[for … : …]) to loop over each instance of thenull_resourceresource and extract thenametrigger value from each one.
Using for_each on a list of strings:
provider "null" {}
variable "users" {
type = list(object({
name = string
age = number
}))
default = [
{ name = "user1", age = 30 },
{ name = "user2", age = 25 },
{ name = "user3", age = 40 },
]
}
resource "null_resource" "users" {
for_each = { for u in var.users : u.name => u }
triggers = {
name = each.key
age = each.value.age
}
}
output "users_with_tags" {
value = { for user in null_resource.users : user.triggers.name => user.triggers.age }
}Code explanation
Line 3–13:
This block declares a variable named
users.The variable has a type of
list(object({ name = string, age = number })), meaning it is a list of objects withnameas a string andageas a number.The default value of the variable is set to a list of three objects, each containing a
nameand anagefield for three users.
Line 15–22:
This block defines a
null_resourcenamedusers.The
for_eachargument uses a for-loop with theforexpression to create a map, where the keys are thenamefields from the objects in theuserslist and the values are the full objects.Inside the
triggersblock, a trigger is set for each instance of thenull_resourceusing thenameandagefields from each corresponding object.
Line 24–26:
This block defines an output named
users_with_tags.The value of the output is set using a map comprehension (
{ for … : … }) to loop over each instance of thenull_resourceresource and extract thenameas the key andageas the value from each trigger.
