Selectively apply VM configuration updates in a MIG

This document describes how to selectively apply configuration updates to the virtual machine (VM) instances in a managed instance group (MIG).

Compute Engine maintains the VMs in a MIG based on the configuration components that you use: instance template, optional all-instances configuration, and optional stateful configuration.

Whenever you update a MIG's VM configuration by changing those components, Compute Engine automatically applies your updated configuration to new VMs that are added to the group.

To apply an updated configuration to existing VMs, you can set up a selective update–also known as a "opportunistic" update type. This type of update offers the following advantages:

You can select the VMs that you want to update.

You can control the timing and the sequence of the updates.

You can use the gcloud CLI or REST to update all VMs immediately.

Before you begin

Apply updated configuration to selected VMs

Ensure your group's update policy type is set to "opportunistic" to prevent the MIG from automatically applying new a VM configuration to existing VMs. For more information, see Check your group's update policy type.

Then use the gcloud CLI or REST to update your MIG's configuration and to apply the latest configuration to specific VMs in the group or to all VMs in the group.

Permissions required for this task

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

For zonal MIGs, all permissions required to call the instanceGroupManagers.patch method
For regional MIGs, all permissions required to call the regionInstanceGroupManagers.patch method

gcloud

To set up a new instance template for your group, you can use the set-instance-template command.

gcloud compute instance-groups managed set-instance-template INSTANCE_GROUP_NAME \
    --template=INSTANCE_TEMPLATE

Apply configuration to specific VMs

To apply the updated configuration to specific VMs, use the update-instances command with the --instances flag.

gcloud compute instance-groups managed update-instances INSTANCE_GROUP_NAME \
    --instances INSTANCE_NAMES \
    --most-disruptive-allowed-action DISRUPTION_LEVEL \
    --minimal-action DISRUPTION_LEVEL

Apply configuration to all VMs

To apply the updated configuration to all VMs, use the update-instances command with the --all-instances flag.

gcloud compute instance-groups managed update-instances INSTANCE_GROUP_NAME \
    --all-instances \
    --most-disruptive-allowed-action DISRUPTION_LEVEL \
    --minimal-action DISRUPTION_LEVEL

Replace the following:

INSTANCE_GROUP_NAME: the name of the MIG
INSTANCE_TEMPLATE: new instance template
INSTANCE_NAMES: a list of VMs to apply the template to
DISRUPTION_LEVEL: the minimal or maximal disruption level: none, refresh, restart, or replace
- The default minimal action is none
- The default most disruptive allowed action is replace

REST

To set up a new instance template for your group, call the patch method on a zonal or regional MIG and update the versions.instanceTemplate field. To avoid automatically rolling out the new template to all VMs in the group, set the updatePolicy.type field to OPPORTUNISTIC.

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

{
  "updatePolicy": {
    "type": "OPPORTUNISTIC"
  },
  "versions": [{
    "instanceTemplate": "global/instanceTemplates/NEW_TEMPLATE",
  }]
}

Apply configuration to specific VMs

To apply the updated configuration to specific VMs, call the applyUpdatesToInstances method for your zonal or regional MIG and specify a list of VMs in the request.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/regions/REGION/instanceGroupManagers/INSTANCE_GROUP_NAME/applyUpdatesToInstances
{
  "instances": [
    "zones/ZONE/instances/INSTANCE_NAME_1",
    "zones/ZONE/instances/INSTANCE_NAME_2"
  ],
  "minimalAction": DISRUPTION_LEVEL,
  "mostDisruptiveAllowedAction": DISRUPTION_LEVEL
}

Apply configuration to all VMs

To apply the updated configuration to all existing VMs, set the allInstances field to true:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/regions/REGION/instanceGroupManagers/INSTANCE_GROUP_NAME/applyUpdatesToInstances
{
  "allInstances": true,
  "minimalAction": DISRUPTION_LEVEL,
  "mostDisruptiveAllowedAction": DISRUPTION_LEVEL
}

Replace the following:

INSTANCE_GROUP_NAME: the name of the group
NEW_TEMPLATE: the name of the new template
ZONE: the zone of an instance to update
INSTANCE_NAME_1 and INSTANCE_NAME_2: the names of the VMs to update
DISRUPTION_LEVEL: the minimal or maximal disruption level: NONE, REFRESH, RESTART, or REPLACE
- The default minimalAction is NONE.
- The default mostDisruptiveAllowedAction is REPLACE.

Similar to other managed instance group methods, applyUpdatesToInstances is intent-based, which means it returns an operation response. The operation can take some time to complete.

After you make a request, you can check the status to verify that the update is complete.

Control the disruption level during selective updates

Depending on the nature of an update, it might disrupt an instance's state. For example, changing an instance's boot disk requires replacing the instance. You can control the level of disruption during a selective update by setting the following options:

Minimal action: Use this option to minimize disruption as much as possible or to apply a more disruptive action than is necessary.
- To limit disruption as much as possible, set the minimal action to NONE. If your update requires a more disruptive action, Compute Engine performs the necessary action to execute the update.
- To apply a more disruptive action than is strictly necessary, set the minimal action to RESTART or REPLACE. For example, Compute Engine does not need to restart a VM to change its metadata. But if your application reads instance metadata only when a VM is restarted, you can set the minimal action to RESTART in order to pick up metadata changes.
Most disruptive allowed action: Use this option to prevent an update if it requires more disruption than you can afford. If your update requires a more disruptive action than you set with this flag, the update request fails. For example, if you set the most disruptive allowed action to RESTART, then an attempt to update the boot disk image fails because that update requires instance recreation, a more disruptive action than a restart.

When updating selected VMs, both of these options accept the following values:

Value	Description	Which instance properties can be updated?
`NONE`	Don't disrupt the instance at all.	None
`REFRESH`	Don't stop the instance.	Additional disks, Dynamic Network Interfaces (NICs), instance metadata, labels, tags
`RESTART`	Stop the instance and start it again.	Additional disks, Dynamic NICs, instance metadata, labels, tags, machine type
`REPLACE`	Delete the instance and create it again.	All instance properties stored in the instance template or per-instance configuration

The most disruptive allowed action can't be less disruptive than the minimal action.

When you selectively update VMs, the following defaults apply:

The default minimal action is NONE, which limits disruption as much as possible.
The default most disruptive allowed action is REPLACE. If you cannot tolerate such disruption, set the most disruptive allowed action to be less disruptive.

What's next

Learn about Viewing info about MIGs and managed VMs.
Learn about Creating instance templates.
Learn how to use image families and a rolling replace to update the OS image on all VMs in a MIG.

Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.

Last updated 2026-07-17 UTC.

Selectively apply VM configuration updates in a MIG Stay organized with collections Save and categorize content based on your preferences.

Before you begin

Console

gcloud

REST

Apply updated configuration to selected VMs

Permissions required for this task

gcloud

REST

Control the disruption level during selective updates

What's next

Selectively apply VM configuration updates in a MIG