Create a MIG with VMs in multiple zones in a region

This document describes how to create a managed instance group (MIG) that has its VMs spread across multiple zones in a region. Spreading your application load across multiple zones protects your workload against zonal failures. If a zonal failure happens, your application can continue serving from instances running in the remaining available zones in the same region.

This type of MIG is also known as a regional MIG. For more information, see About regional MIGs.

You can also read about other basic scenarios for creating a MIG.

Before you begin

Create an instance template, which is required in order to create a managed instance group.
If you haven't already, then set up authentication. Authentication is the process by which your identity is verified for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:

Select the tab for how you plan to use the samples on this page:
Console

When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.
gcloud
1. Install the Google Cloud CLI, then initialize it by running the following command:
  gcloud init
  Note: If you installed the gcloud CLI previously, make sure you have the latest version by running gcloud components update.
2. Set a default region and zone.
Terraform

To use the Terraform samples on this page in a local development environment, install and initialize the gcloud CLI, and then set up Application Default Credentials with your user credentials.
1. Install the Google Cloud CLI.
2. To initialize the gcloud CLI, run the following command:
  gcloud init
3. If you're using a local shell, then create local authentication credentials for your user account:
```
gcloud auth application-default login
```
  You don't need to do this if you're using Cloud Shell.
For more information, see Set up authentication for a local development environment.
REST

To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.
For more information, see Authenticate for using REST in the Google Cloud authentication documentation.

Limitations

To see the full list of MIG limitations, which varies based on the configuration that you use, see MIG limitations.

Create a MIG with VMs in multiple zones in a region

Use the Google Cloud console , the gcloud CLI, Terraform, or REST.

Permissions required for this task

To perform this task, you must have the following permissions:

All permissions required to call the regionInstanceGroupManagers.insert method.

Console

In the Google Cloud console, go to the Instance groups page.

Go to Instance groups

The remaining steps appear in the Google Cloud console.
Click Create instance group to create a new instance group.
Select one of the New managed instance group options:
- Stateless (default)
- Stateful
Assign a name and optionally a description to your instance group.
Choose an instance template for the instance group or create a new one.
In Number of instances or in Autoscaling, specify the number of instances for this group. Remember to provision enough VMs to support your application if a zone failure happens.
For Location, select Multiple zones.
Choose a region and select the zones you want to use. If you chose a regional instance template, then the Region is automatically selected based on the template's region.
Under Target distribution shape, select Even. If you want to select a different shape, see Set a target distribution shape for VMs in a regional MIG.
If you want to disable proactive instance redistribution, then under Instance redistribution, deselect the Allow instance redistribution checkbox.
Continue with the rest of the MIG creation process.
To create the MIG, click Create.

gcloud

All MIGs require an instance template. If you don't have one, create an instance template. For example, the following command creates a basic instance template with default properties:

gcloud compute instance-templates create example-template

Next, use the instance-groups managed create command with the --region flag. For example, the following command creates a regional MIG in three zones within the us-east1 region:

gcloud compute instance-groups managed create example-rmig \
    --template example-template  \
    --size 30 \
    --region us-east1

If you want to select specific zones that the group should use, provide the --zones flag:

gcloud compute instance-groups managed create example-rmig \
    --template example-template \
    --size 30 \
    --zones us-east1-b,us-east1-c

If you want to disable proactive instance redistribution, see Turning off proactive instance redistribution.

Terraform

If you haven't already created an instance template, which specifies the machine type, boot disk image, network, and other VM properties that you want for each VM in your MIG, create an instance template.

To create a regional MIG, you can use the google_compute_region_instance_group_manager resource.

resource "google_compute_region_instance_group_manager" "default" {
  name                      = "example-rmig"
  region                    = "us-east1"
  distribution_policy_zones = ["us-east1-b", "us-east1-c"]
  target_size               = 30
  base_instance_name        = "instance"
  version {
    instance_template = google_compute_instance_template.default.id
  }
}

To learn how to apply or remove a Terraform configuration, see Basic Terraform commands.

REST

All MIGs require an instance template. If you don't have one, create an instance template.

Next, construct a POST request to the regionInstanceGroupManagers.insert method. In the request body, specify the group name, group size, and the URL to the instance template. Optionally, specify other fields, such as the base name for instances in the group.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/regions/REGION/instanceGroupManagers

{
  "baseInstanceName": "BASE_INSTANCE_NAME",
  "instanceTemplate": "global/instanceTemplates/INSTANCE_TEMPLATE_NAME",
  "name": "INSTANCE_GROUP_NAME",
  "targetSize": "TARGET_SIZE"
}

Replace the following:

PROJECT_ID: the project ID for this request.
REGION: the region for the group.
BASE_INSTANCE_NAME: (optional) the instance name for each VM instance that is created as part of the group. For example, a base instance name of example-instance creates instances that have names like example-instance-[RANDOM_STRING] where [RANDOM_STRING] is generated by the server.
INSTANCE_TEMPLATE_NAME: the instance template to use. For a regional instance template, you must specify the full or partial URL of the template. An example of a full URL is https://www.googleapis.com/compute/v1/projects/example-project/regions/us-central1/instanceTemplates/example-regional-instance-template and a partial URL is projects/example-project/regions/us-central1/instanceTemplates/example-regional-instance-template.
INSTANCE_GROUP_NAME: the name of the MIG.
TARGET_SIZE: the target number of VMs for the group.

If you want to select specific zones or if you are creating VMs in a region with less than or more than three zones, include the distributionPolicy property in your request and supply a list of zones. Replace ZONE with the name of a zone to create VMs in.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/regions/REGION/instanceGroupManagers

{
  "baseInstanceName": "BASE_INSTANCE_NAME",
  "instanceTemplate": "global/instanceTemplates/INSTANCE_TEMPLATE_NAME",
  "name": "INSTANCE_GROUP_NAME",
  "targetSize": "TARGET_SIZE",
  "distributionPolicy": {
     "zones": [
       {"zone": "zones/ZONE"},
       {"zone": "zones/ZONE"}
      ]
   }
}

For example, the following creates a regional MIG named example-rmig with 10 managed instances distributed across us-east1-b and us-east1-c zones:

POST https://compute.googleapis.com/compute/v1/projects/myproject/regions/us-east1/instanceGroupManagers

{
  "instanceTemplate": "global/instanceTemplates/example-instance",
  "name": "example-rmig",
  "targetSize": 10,
  "distributionPolicy": {
      "zones": [
        {"zone": "zones/us-east1-b"},
        {"zone": "zones/us-east1-c"}
      ]
   }
}

Depending on how you configure and act on a MIG, various policies and actions can affect the instances in the group. To determine which managed instances are up and running, see Checking the status of managed instances.

If there is not enough capacity in each zone to support VMs for the group, Compute Engine creates as many VMs as possible and continues attempting to create the remaining VMs when additional capacity becomes available.

If you do not explicitly specify individual zones in your request, Compute Engine automatically chooses three zones to create VMs in. If you need to create VMs in more than or fewer than three zones, or you want to pick which zones are used, you can provide a list of zones in your request. For more information, see Zone selection.

Distribution of VMs across zones

By default, a regional MIG distributes VMs evenly across selected zones. Because you are creating a regional MIG, keep in mind that certain resources are zonal, such as GPUs and existing persistent disks. If your MIG's instance template specifies zonal resources, you must make sure all those resources are present in all selected zones so they can be attached to the VMs created by the regional MIG. Alternatively, if you want the group to check for the existence of zonal resources for you, you can set the MIG's target distribution shape to create instances only in zones that contain those resources.

For more information, see the following documents:

Set a target distribution shape for VMs across zones

Proactive instance redistribution

Proactive instance redistribution is enabled by default. If you need to manually manage the number of VMs in each zone, or if you need to set the MIG's target distribution shape to BALANCED or ANY_SINGLE_ZONE, you must disable proactive instance redistribution.

For more information, see the following docs:

What's next

Set up application-based autohealing, which periodically verifies that your application responds as expected on each of the MIG's VMs and automatically recreates unresponsive VMs.
Enable autoscaling to automatically add or delete VMs from your MIG based on increases or decreases in load.
Learn how to apply a new configuration to all or to a subset of the VMs in a MIG by setting and applying a new instance template, all-instances configuration, or per-instance configuration.
Preserve disks, metadata, and IP addresses across disruptive events like VM recreation, autohealing, and updates by adding stateful configuration.
Learn about working with managed instances, for example, to delete, abandon, and recreate VMs in a MIG.
View info about MIGs and their VMs.
Simulate a zone outage for a regional MIG
Learn how to add an external HTTP(S) load balancer frontend to your instance group. For information about other types of load balancers, see the Load balancing overview.