Terraform: Introduction to primitives and complex data types
Overview of data types in Terraform — string, number, bool, list/tuple, and map/set
In this post, we will take a brief look at the data types that we can use in Terraform to better understand the topic of the following post — Terraform: count, for_each, and for loops.
Documentation — Type Constraints and Types and Values.
We have the following types divided into groups:
- Primitive Types:
-
string: sequence of Unicode characters, plain text -
number: numerical values -
bool: true or false - Complex Types:
- Collection Types:
-
list: alistis a type of structure for storing a simple collection of values of the same type, accessible by index -
map: a key:value collection of values of the same type - s
et: similar to thelist, but without indexes and sorting - Structural Types:
-
object: to store values of different data types – a set of named attributes, each with its own data type -
tuple: a sequence of elements, each with its own data type, indexed as in thelist
Primitive types
The simplest type, in which we can store only one value of a certain type.
string
An example:
variable "var_string" {
type = string
default = "a string"
}
output "string" {
value = var.var_string
}
The result is obvious:
...
Outputs:
string = "a string"
number
Similarly, but for integer values:
variable "var_number" {
type = number
default = 1
}
output "number" {
value = var.var_number
}
Result:
...
Outputs:
number = 1
bool
Used for the Conditional Expressions:
variable "var_bool" {
type = bool
default = true
}
output "number" {
value = var.var_bool ? "True" : "False"
}
Result:
...
Outputs:
number = "True"
Or creating a resource if the condition is valid:
resource "local_file" "file" {
count = var.var_bool ? 1 : 0
filename = "file.txt"
content = var.var_string
}
Collection Types
list
A sequence of values of the same type with indices starting from zero.
When creating a list, you can either not specify the type (default == any), or limit it to one specific type:
variable "var_list_any" {
type = list
default = ["a string", 10]
}
variable "var_list_string" {
type = list(string)
default = ["first string", "second string"]
}
resource "local_file" "file" {
filename = "file-${var.var_list_any[1]}.txt"
content = var.var_list_string[0]
}
output "list_any" {
value = var.var_list_any
}
output "list_string" {
value = var.var_list_string
}
Result:
...
Outputs:
list_any = tolist([
"a string",
"10",
])
list_string = tolist([
"first string",
"second string",
])
And the file:
$ cat file-10.txt
first string
Within a list you can use other data types – other list, map, etc.
At the same time, in a list we can have different types of primitives (string, number, bool), but the same type for other types, i.e.:
variable "var_list_any" {
type = list
default = ["a", true, 1]
}
variable "var_list_lists" {
type = list
default = [
["a", "b"],
["c", "d"]
]
}
output "list_any" {
value = var.var_list_any
}
output "list_lists" {
value = var.var_list_lists
}
Result:
...
Outputs:
list_any = tolist([
"a",
"true",
"1",
])
list_lists = tolist([
[
"a",
"b",
],
[
"c",
"d",
],
])
With the list we can use loops, for example:
variable "var_list_any" {
type = list
default = ["a string", 10]
}
variable "var_list_string" {
type = list(string)
default = ["first string", "second string"]
}
resource "local_file" "file" {
for_each = toset(var.var_list_any)
filename = "file-${each.key}.txt"
content = each.value
}
output "list_string" {
value = [for a in var.var_list_string : upper(a)]
}
Result:
...
Outputs:
list_string = [
"FIRST STRING",
"SECOND STRING",
]
And files:
$ ls -1
file-10.txt
'file-a string.txt'
$ cat file-a\ string.txt
a string
map
A value in the key:value form with access to the value by the key name:
variable "var_map" {
type = map
default = {
"one" = "first",
"two" = "second"
}
}
output "map_one" {
value = var.var_map["one"]
}
output "map_two" {
value = var.var_map["two"]
}
We can also display the attribute in outputs, i.e. value = var.var\_map.one.
Result:
...
Outputs:
map_one = "first"
map_two = "second"
We can also use the lookup() to search for values in a map by a key:
output "map_lookup" {
value = lookup(var.var_map, "one", "None")
}
Result:
...
Outputs:
map_lookup = "first"
map_one = "first"
map_two = "second"
Or a more complex example — choosing a number of instances by the price depending on the instance type:
variable "instance_cost" {
type = map
default = {
"t3.medium" = "0.04USD",
"t3.large" = "0.08USD",
}
}
variable "instance_number" {
type = map
default = {
"0.04USD" = 2,
"0.08USD" = 1,
}
}
output "instances_count" {
value = lookup(var.instance_number, var.instance_cost["t3.medium"], 0)
}
Result:
...
Outputs:
instances_count = 2
A map can also include a list or another map, but all objects must be of the same type (that is, you cannot have a map with a list in a first item, and another map in a second):
variable "var_map_of_maps" {
type = map
default = {
"out-map-key-1" = {
"in-map-key-1" = "inner map 1 key one",
"in-map-key-2" = "inner map 1 inner key two",
},
"out-map-key-2" = {
"in-map-key-1" = "inner map 2 key one",
"in-map-key-2" = "inner map 2 key two",
},
}
}
output "map_of_maps" {
value = var.var_map_of_maps
}
Result:
...
Outputs:
map_of_maps = tomap({
"out-map-key-1" = {
"in-map-key-1" = "inner map 1 key one"
"in-map-key-2" = "inner map 1 inner key two"
}
"out-map-key-2" = {
"in-map-key-1" = "inner map 2 key one"
"in-map-key-2" = "inner map 2 key two"
}
})
set
A sequence of values of the same or different types as in list, but without indexes and sorting:
variable "var_set_any" {
type = set(any)
default = ["string", 1]
}
variable "var_set_string" {
type = set(string)
default = ["string1", "string2"]
}
output "set_any" {
value = var.var_set_any
}
output "set_string" {
value = var.var_set_string
}
Result:
...
...
Outputs:
set_any = toset([
"1",
"string",
])
set_string = toset([
"string1",
"string2",
])
Like with list or map, a set can have nested types:
variable "var_set_lists" {
type = set(list(any))
default = [
["a", "b"],
["c", "d"]
]
}
output "set_any" {
value = var.var_set_lists
}
Result:
...
set_any = toset([
tolist([
"a",
"b",
]),
tolist([
"c",
"d",
]),
])
Structural Types
object
Unlike map and list, object is a structural type that can have values of various types, including several list and map.
Similar to Struct in C or Golang:
variable "var_object" {
type = object({
name = string,
id = number,
data = list(string)
data_map = map(any)
})
default = {
name = "one",
id = 10,
data = ["first", "second"],
data_map = {
"one" = "first",
"two" = "second"
}
}
}
output "object" {
value = var.var_object
}
output "object_map" {
value = var.var_object.data_map
}
Result:
...
Outputs:
object = {
"data" = tolist([
"first",
"second",
])
"data_map" = tomap({
"one" = "first"
"two" = "second"
})
"id" = 10
"name" = "one"
}
object_map = tomap({
"one" = "first"
"two" = "second"
})
tuple
Similar to the object, but with indexes instead of key names:
variable "var_tuple" {
type = tuple ([
string,
number,
list(string),
map(any)
] )
default = [
"one",
10,
["first", "second"],
{
"one" = "first",
"two" = "second"
}
]
}
output "tuple" {
value = var.var_tuple
}
output "tuple_map" {
value = var.var_tuple[3]
}
Result:
Outputs:
tuple = [
"one",
10,
tolist([
"first",
"second",
]),
tomap({
"one" = "first"
"two" = "second"
}),
]
tuple_map = tomap({
"one" = "first"
"two" = "second"
})
In the next post, we will look at loops in Terraform.
Originally published at RTFM: Linux, DevOps, and system administration.
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