# GCE Managed Instance Group module
This module allows creating a managed instance group supporting one or more application versions via instance templates. A health check and an autoscaler can also be optionally created.
This module can be coupled with the [`compute-vm`](../compute-vm) module which can manage instance templates, and the [`net-ilb`](../net-ilb) module to assign the MIG to a backend wired to an Internal Load Balancer. The first use case is shown in the examples below.
## Examples
This example shows how to manage a simple MIG that leverages the `compute-vm` module to manage the underlying instance template. The following sub-examples will only show how to enable specific features of this module, and won't replicate the combined setup.
```hcl
module "cos-nginx" {
source = "./modules/cloud-config-container/nginx"
}
module "nginx-template" {
source = "./modules/compute-vm"
project_id = var.project_id
name = "nginx-template"
zone = "europe-west1-b"
tags = ["http-server", "ssh"]
network_interfaces = [{
network = var.vpc.self_link
subnetwork = var.subnet.self_link
nat = false
addresses = null
}]
boot_disk = {
image = "projects/cos-cloud/global/images/family/cos-stable"
type = "pd-ssd"
size = 10
}
create_template = true
metadata = {
user-data = module.cos-nginx.cloud_config
}
}
module "nginx-mig" {
source = "./modules/compute-mig"
project_id = "my-project"
location = "europe-west1-b"
name = "mig-test"
target_size = 2
default_version = {
instance_template = module.nginx-template.template.self_link
name = "default"
}
}
# tftest:modules=2:resources=2
```
### Multiple versions
If multiple versions are desired, use more `compute-vm` instances for the additional templates used in each version (not shown here), and reference them like this:
```hcl
module "cos-nginx" {
source = "./modules/cloud-config-container/nginx"
}
module "nginx-template" {
source = "./modules/compute-vm"
project_id = var.project_id
name = "nginx-template"
zone = "europe-west1-b"
tags = ["http-server", "ssh"]
network_interfaces = [{
network = var.vpc.self_link
subnetwork = var.subnet.self_link
nat = false
addresses = null
}]
boot_disk = {
image = "projects/cos-cloud/global/images/family/cos-stable"
type = "pd-ssd"
size = 10
}
create_template = true
metadata = {
user-data = module.cos-nginx.cloud_config
}
}
module "nginx-mig" {
source = "./modules/compute-mig"
project_id = "my-project"
location = "europe-west1-b"
name = "mig-test"
target_size = 3
default_version = {
instance_template = module.nginx-template.template.self_link
name = "default"
}
versions = {
canary = {
instance_template = module.nginx-template.template.self_link
target_type = "fixed"
target_size = 1
}
}
}
# tftest:modules=2:resources=2
```
### Health check and autohealing policies
Autohealing policies can use an externally defined health check, or have this module auto-create one:
```hcl
module "cos-nginx" {
source = "./modules/cloud-config-container/nginx"
}
module "nginx-template" {
source = "./modules/compute-vm"
project_id = var.project_id
name = "nginx-template"
zone = "europe-west1-b"
tags = ["http-server", "ssh"]
network_interfaces = [{
network = var.vpc.self_link,
subnetwork = var.subnet.self_link,
nat = false,
addresses = null
}]
boot_disk = {
image = "projects/cos-cloud/global/images/family/cos-stable"
type = "pd-ssd"
size = 10
}
create_template = true
metadata = {
user-data = module.cos-nginx.cloud_config
}
}
module "nginx-mig" {
source = "./modules/compute-mig"
project_id = "my-project"
location = "europe-west1-b"
name = "mig-test"
target_size = 3
default_version = {
instance_template = module.nginx-template.template.self_link
name = "default"
}
auto_healing_policies = {
health_check = module.nginx-mig.health_check.self_link
initial_delay_sec = 30
}
health_check_config = {
type = "http"
check = { port = 80 }
config = {}
logging = true
}
}
# tftest:modules=2:resources=3
```
### Autoscaling
The module can create and manage an autoscaler associated with the MIG. When using autoscaling do not set the `target_size` variable or set it to `null`. Here we show a CPU utilization autoscaler, the other available modes are load balancing utilization and custom metric, like the underlying autoscaler resource.
```hcl
module "cos-nginx" {
source = "./modules/cloud-config-container/nginx"
}
module "nginx-template" {
source = "./modules/compute-vm"
project_id = var.project_id
name = "nginx-template"
zone = "europe-west1-b"
tags = ["http-server", "ssh"]
network_interfaces = [{
network = var.vpc.self_link
subnetwork = var.subnet.self_link
nat = false
addresses = null
}]
boot_disk = {
image = "projects/cos-cloud/global/images/family/cos-stable"
type = "pd-ssd"
size = 10
}
create_template = true
metadata = {
user-data = module.cos-nginx.cloud_config
}
}
module "nginx-mig" {
source = "./modules/compute-mig"
project_id = "my-project"
location = "europe-west1-b"
name = "mig-test"
target_size = 3
default_version = {
instance_template = module.nginx-template.template.self_link
name = "default"
}
autoscaler_config = {
max_replicas = 3
min_replicas = 1
cooldown_period = 30
cpu_utilization_target = 0.65
load_balancing_utilization_target = null
metric = null
}
}
# tftest:modules=2:resources=3
```
### Update policy
```hcl
module "cos-nginx" {
source = "./modules/cloud-config-container/nginx"
}
module "nginx-template" {
source = "./modules/compute-vm"
project_id = var.project_id
name = "nginx-template"
zone = "europe-west1-b"
tags = ["http-server", "ssh"]
network_interfaces = [{
network = var.vpc.self_link
subnetwork = var.subnet.self_link
nat = false
addresses = null
}]
boot_disk = {
image = "projects/cos-cloud/global/images/family/cos-stable"
type = "pd-ssd"
size = 10
}
create_template = true
metadata = {
user-data = module.cos-nginx.cloud_config
}
}
module "nginx-mig" {
source = "./modules/compute-mig"
project_id = "my-project"
location = "europe-west1-b"
name = "mig-test"
target_size = 3
default_version = {
instance_template = module.nginx-template.template.self_link
name = "default"
}
update_policy = {
type = "PROACTIVE"
minimal_action = "REPLACE"
min_ready_sec = 30
max_surge_type = "fixed"
max_surge = 1
max_unavailable_type = null
max_unavailable = null
}
}
# tftest:modules=2:resources=2
```
## Variables
| name | description | type | required | default |
|---|---|:---: |:---:|:---:|
| default_version | Default application version template. Additional versions can be specified via the `versions` variable. | object({...}) | ✓ | |
| location | Compute zone, or region if `regional` is set to true. | string | ✓ | |
| name | Managed group name. | string | ✓ | |
| project_id | Project id. | string | ✓ | |
| *auto_healing_policies* | Auto-healing policies for this group. | object({...}) | | null |
| *autoscaler_config* | Optional autoscaler configuration. Only one of 'cpu_utilization_target' 'load_balancing_utilization_target' or 'metric' can be not null. | object({...}) | | null |
| *health_check_config* | Optional auto-created health check configuration, use the output self-link to set it in the auto healing policy. Refer to examples for usage. | object({...}) | | null |
| *named_ports* | Named ports. | map(number) | | null |
| *regional* | Use regional instance group. When set, `location` should be set to the region. | bool | | false |
| *target_pools* | Optional list of URLs for target pools to which new instances in the group are added. | list(string) | | [] |
| *target_size* | Group target size, leave null when using an autoscaler. | number | | null |
| *update_policy* | Update policy. Type can be 'OPPORTUNISTIC' or 'PROACTIVE', action 'REPLACE' or 'restart', surge type 'fixed' or 'percent'. | object({...}) | | null |
| *versions* | Additional application versions, target_type is either 'fixed' or 'percent'. | map(object({...})) | | null |
| *wait_for_instances* | Wait for all instances to be created/updated before returning. | bool | | null |
## Outputs
| name | description | sensitive |
|---|---|:---:|
| autoscaler | Auto-created autoscaler resource. | |
| group_manager | Instance group resource. | |
| health_check | Auto-created health-check resource. | |
## TODO
- [ ] add support for instance groups