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

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 console , the gcloud CLI or the Compute Engine API.

Console

  1. In the console, go to the Instance groups page.

    Go to the Instance groups page

  2. Click Create instance group to create a new instance group.
  3. Select one of the New managed instance group options:
  4. Assign a name and optionally a description to your instance group.
  5. Choose an instance template for the instance group or create a new one.
  6. 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.
  7. Under Location, select Multiple zones.
  8. Choose a region and select the zones you want to use.
  9. 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.
  10. If you want to disable proactive instance redistribution:
    1. Ensure that Autoscaling mode is set to Off: do not autoscale.
    2. Under Instance redistribution, deselect the Enable instance redistribution checkbox.
  11. Continue with the rest of the MIG creation process.

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, set the --instance-redistribution-type flag to NONE. You cannot disable proactive instance redistribution if autoscaling is enabled.

gcloud compute instance-groups managed create example-rmig \
    --template example-template \
    --size 30 \
    --instance-redistribution-type NONE \
    --region us-east1

API

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: the instance name for each VM instance that is created as part of the group. For example, a base instance name of example-instance would create 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.
  • 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:

Proactive instance redistribution

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

For more information, see the following docs:

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