How to for_each through a list(objects) in Terraform 0.12
ListLoopsObjectForeachTerraformList Problem Overview
I need to deploy a list of GCP compute instances. How do I loop for_each through the "vms" in a list of objects like this:
"gcp_zone": "us-central1-a",
"image_name": "centos-cloud/centos-7",
"vms": [
{
"hostname": "test1-srfe",
"cpu": 1,
"ram": 4,
"hdd": 15,
"log_drive": 300,
"template": "Template-New",
"service_types": [
"sql",
"db01",
"db02"
]
},
{
"hostname": "test1-second",
"cpu": 1,
"ram": 4,
"hdd": 15,
"template": "APPs-Template",
"service_types": [
"configs"
]
}
]
}
List Solutions
Solution 1 - List
Seem's like I found what to do. If you pass not the maps of maps but the list of maps you can use such code
resource "google_compute_instance" "node" {
for_each = {for vm in var.vms: vm.hostname => vm}
name = "${each.value.hostname}"
machine_type = "custom-${each.value.cpu}-${each.value.ram*1024}"
zone = "${var.gcp_zone}"
boot_disk {
initialize_params {
image = "${var.image_name}"
size = "${each.value.hdd}"
}
}
network_interface {
network = "${var.network}"
}
metadata = {
env_id = "${var.env_id}"
service_types = "${join(",",each.value.service_types)}"
}
}
It will create actual number of instance and when you remove for example middle one of three(if you create three:)), terraform will remove what we asked.
Solution 2 - List
I work a lot with iterators in Terraform, they always gave me bad headaches. Therefore I identified three of the most common iterator patterns (code examples are given below), which helped me construct a lot of nice modules (source).
- Using for_each on a list of strings
- Using for_each on a list of objects
- Using for_each as a conditional
Using for_each and a list of strings is the easiest to understand, you can always use the toset() function. When working with a list of objects you need to convert it to a map where the key is a unique value. The alternative is to put a map inside your Terraform configuration. Personally, I think it looks cleaner to have a list of objects instead of a map in your configuration. The key usually doesn't have a purpose other than to identify unique items in a map, which can thus be constructed dynamically. I also use iterators to conditionally deploy a resource or resource block, especially when constructing more complex modules.
Using for_each on a list of strings
locals {
ip_addresses = ["10.0.0.1", "10.0.0.2"]
}
resource "example" "example" {
for_each = toset(local.ip_addresses)
ip_address = each.key
}
Using for_each on a list of objects
locals {
virtual_machines = [
{
ip_address = "10.0.0.1"
name = "vm-1"
},
{
ip_address = "10.0.0.1"
name = "vm-2"
}
]
}
resource "example" "example" {
for_each = {
for index, vm in local.virtual_machines:
vm.name => vm # Perfect, since VM names also need to be unique
# OR: index => vm (unique but not perfect, since index will change frequently)
# OR: uuid() => vm (do NOT do this! gets recreated everytime)
}
name = each.value.name
ip_address = each.value.ip_address
}
Using for_each as a conditional
variable "deploy_something" {
type = bool
description = "Indicates whether to deploy something."
default = true
}
# Using count and a conditional, for_each is also possible here.
# See the next solution using a for_each with a conditional.
resource "example" "example" {
count = var.deploy_example ? 0 : 1
name = ...
ip_address = ...
}
variable "enable_something" {
type = bool
description = "Indicates whether to enable something."
default = false
}
resource "example" "example" {
name = ...
ip_address = ...
# Note: dynamic blocks cannot use count!
# Using for_each with an empty list and list(1) as a readable alternative.
dynamic "logs" {
for_each = var.enable_logs ? [] : [1]
content {
name = "logging"
}
}
}
Solution 3 - List
From Terraform 0.12, you can use the for_each with modules like the following:
modules/google_compute_instance/variables.tf
variable "hosts" {
type = map(object({
hostname = string
cpu = number
ram = number
hdd = number
log_drive = number
template = string
service_types = list(string)
}))
}
modules/google_compute_instance/main.tf
resource "google_compute_instance" "gcp_instance" {
for_each = var.hosts
hostname = each.value.repository_name
cpu = each.value.cpu
ram = each.value.ram
hdd = each.value.hdd
log_drive = each.value.log_drive
template = each.value.template
service_types = each.value.service_types
}
#servers.tf
module "gcp_instances" {
source = "./modules/google_compute_instance"
hosts = {
"test1-srfe" = {
hostname = "test1-srfe",
cpu = 1,
ram = 4,
hdd = 15,
log_drive = 300,
template = "Template-New",
service_types = ["sql", "db01", "db02"]
},
"test1-second" = {
hostname = "test1-second",
cpu = 1,
ram = 4,
hdd = 15,
log_drive = 300,
template = "APPs-Template",
service_types = ["configs"]
},
}
}
Of course, you can add as many variables as needed and use them in the module.
Solution 4 - List
You can do the following:
for_each = toset(keys({for i, r in var.vms: i => r}))
cpu = var.vms[each.value]["cpu"]
Assuming you had the following:
variable "vms" {
type = list(object({
hostname = string
cpu = number
ram = number
hdd = number
log_drive = number
template = string
service_types = list(string)
}))
default = [
{
cpu: 1
...
}
]
}
Solution 5 - List
Using the for_each block is pretty new and there's not too much documentation. Some of the best info comes from their announcement blog post: https://www.hashicorp.com/blog/hashicorp-terraform-0-12-preview-for-and-for-each/
Also make sure to check out the Dynamic Blocks section of their documentation: https://www.terraform.io/docs/configuration/expressions.html#dynamic-blocks
From what your example looks like you need to have a set of values for each instance that is created so you'll have a map of maps:
Below is an example I created using Terraform 0.12.12:
variable "hostnames" {
default = {
"one" = {
"name" = "one",
"machine" = "n1-standard-1",
"os" = "projects/coreos-cloud/global/images/coreos-stable-2247-5-0-v20191016",
"zone" = "us-central1-a"
},
"two" = {
"name" = "two",
"machine" = "n1-standard-2",
"os" = "projects/centos-cloud/global/images/centos-8-v20191018",
"zone" = "us-central1-b"
}
}
}
resource "google_compute_instance" "default" {
for_each = var.hostnames
name = each.value.name
machine_type = each.value.machine
zone = each.value.zone
boot_disk {
initialize_params {
image = each.value.os
}
}
scratch_disk {
}
network_interface {
network = "default"
}
}
Terraform plan output:
Terraform will perform the following actions:
# google_compute_instance.default["one"] will be created
+ resource "google_compute_instance" "default" {
+ can_ip_forward = false
+ cpu_platform = (known after apply)
+ deletion_protection = false
+ guest_accelerator = (known after apply)
+ id = (known after apply)
+ instance_id = (known after apply)
+ label_fingerprint = (known after apply)
+ machine_type = "n1-standard-1"
+ metadata_fingerprint = (known after apply)
+ name = "one"
+ project = (known after apply)
+ self_link = (known after apply)
+ tags_fingerprint = (known after apply)
+ zone = "us-central1-a"
+ boot_disk {
+ auto_delete = true
+ device_name = (known after apply)
+ disk_encryption_key_sha256 = (known after apply)
+ kms_key_self_link = (known after apply)
+ mode = "READ_WRITE"
+ source = (known after apply)
+ initialize_params {
+ image = "projects/coreos-cloud/global/images/coreos-stable-2247-5-0-v20191016"
+ labels = (known after apply)
+ size = (known after apply)
+ type = (known after apply)
}
}
+ network_interface {
+ address = (known after apply)
+ name = (known after apply)
+ network = "default"
+ network_ip = (known after apply)
+ subnetwork = (known after apply)
+ subnetwork_project = (known after apply)
}
+ scheduling {
+ automatic_restart = (known after apply)
+ on_host_maintenance = (known after apply)
+ preemptible = (known after apply)
+ node_affinities {
+ key = (known after apply)
+ operator = (known after apply)
+ values = (known after apply)
}
}
+ scratch_disk {
+ interface = "SCSI"
}
}
# google_compute_instance.default["two"] will be created
+ resource "google_compute_instance" "default" {
+ can_ip_forward = false
+ cpu_platform = (known after apply)
+ deletion_protection = false
+ guest_accelerator = (known after apply)
+ id = (known after apply)
+ instance_id = (known after apply)
+ label_fingerprint = (known after apply)
+ machine_type = "n1-standard-2"
+ metadata_fingerprint = (known after apply)
+ name = "two"
+ project = (known after apply)
+ self_link = (known after apply)
+ tags_fingerprint = (known after apply)
+ zone = "us-central1-b"
+ boot_disk {
+ auto_delete = true
+ device_name = (known after apply)
+ disk_encryption_key_sha256 = (known after apply)
+ kms_key_self_link = (known after apply)
+ mode = "READ_WRITE"
+ source = (known after apply)
+ initialize_params {
+ image = "projects/centos-cloud/global/images/centos-8-v20191018"
+ labels = (known after apply)
+ size = (known after apply)
+ type = (known after apply)
}
}
+ network_interface {
+ address = (known after apply)
+ name = (known after apply)
+ network = "default"
+ network_ip = (known after apply)
+ subnetwork = (known after apply)
+ subnetwork_project = (known after apply)
}
+ scheduling {
+ automatic_restart = (known after apply)
+ on_host_maintenance = (known after apply)
+ preemptible = (known after apply)
+ node_affinities {
+ key = (known after apply)
+ operator = (known after apply)
+ values = (known after apply)
}
}
+ scratch_disk {
+ interface = "SCSI"
}
}
Plan: 2 to add, 0 to change, 0 to destroy.