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README.md

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 module which can manage instance templates, and the 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.

module "cos-nginx" {
  source = "./modules/cloud-config-container/nginx"
}

module "nginx-template" {
  source     = "./modules/compute-vm"
  project_id = var.project_id
  name       = "nginx-template"
  region     = "europe-west1"
  zones      = ["europe-west1-b", "europe-west1-d"]
  tags       = ["http-server", "ssh"]
  network_interfaces = [{
    network    = var.vpc.self_link
    subnetwork = var.subnet.self_link
    nat        = false
    addresses  = null
    alias_ips  = null
  }]
  boot_disk = {
    image = "projects/cos-cloud/global/images/family/cos-stable"
    type  = "pd-ssd"
    size  = 10
  }
  use_instance_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:

module "cos-nginx" {
  source = "./modules/cloud-config-container/nginx"
}

module "nginx-template" {
  source     = "./modules/compute-vm"
  project_id = var.project_id
  name       = "nginx-template"
  region     = "europe-west1"
  zones      = ["europe-west1-b", "europe-west1-d"]
  tags       = ["http-server", "ssh"]
  network_interfaces = [{
    network    = var.vpc.self_link
    subnetwork = var.subnet.self_link
    nat        = false
    addresses  = null
    alias_ips  = null
  }]
  boot_disk = {
    image = "projects/cos-cloud/global/images/family/cos-stable"
    type  = "pd-ssd"
    size  = 10
  }
  use_instance_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:

module "cos-nginx" {
  source = "./modules/cloud-config-container/nginx"
}

module "nginx-template" {
  source     = "./modules/compute-vm"
  project_id = var.project_id
  name       = "nginx-template"
  region     = "europe-west1"
  zones      = ["europe-west1-b", "europe-west1-d"]
  tags       = ["http-server", "ssh"]
  network_interfaces = [{
    network    = var.vpc.self_link,
    subnetwork = var.subnet.self_link,
    nat        = false,
    addresses  = null
    alias_ips  = null
  }]
  boot_disk = {
    image = "projects/cos-cloud/global/images/family/cos-stable"
    type  = "pd-ssd"
    size  = 10
  }
  use_instance_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.

module "cos-nginx" {
  source = "./modules/cloud-config-container/nginx"
}

module "nginx-template" {
  source     = "./modules/compute-vm"
  project_id = var.project_id
  name       = "nginx-template"
  region     = "europe-west1"
  zones      = ["europe-west1-b", "europe-west1-d"]
  tags       = ["http-server", "ssh"]
  network_interfaces = [{
    network    = var.vpc.self_link
    subnetwork = var.subnet.self_link
    nat        = false
    addresses  = null
    alias_ips  = null
  }]
  boot_disk = {
    image = "projects/cos-cloud/global/images/family/cos-stable"
    type  = "pd-ssd"
    size  = 10
  }
  use_instance_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

module "cos-nginx" {
  source = "./modules/cloud-config-container/nginx"
}

module "nginx-template" {
  source     = "./modules/compute-vm"
  project_id = var.project_id
  name       = "nginx-template"
  region     = "europe-west1"
  zones      = ["europe-west1-b", "europe-west1-d"]
  tags       = ["http-server", "ssh"]
  network_interfaces = [{
    network    = var.vpc.self_link
    subnetwork = var.subnet.self_link
    nat        = false
    addresses  = null
    alias_ips  = null
  }]
  boot_disk = {
    image = "projects/cos-cloud/global/images/family/cos-stable"
    type  = "pd-ssd"
    size  = 10
  }
  use_instance_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