Basic scenarios for creating managed instance groups (MIGs)

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A managed instance group (MIG) is a group of virtual machine (VM) instances that you treat as a single entity. Each VM in a MIG is based on an instance template.

If you only need to create multiple VMs, but don't want them grouped together in a MIG, see the bulk instance API.

To learn about other Compute Engine options, see Choose a Compute Engine deployment strategy for your workload.

To get started with creating a MIG, read this document to find a basic configuration that works for you.

Basic scenarios for creating a MIG

MIGs have many configuration options. See the following guides to quickly get a MIG up and running for various scenarios:

Guide	Scenario
Create a MIG with VMs in a single zone (zonal MIG)	Your VMs can be deployed to a single zone
Create a MIG with VMs in multiple zones in a region (regional MIG)	You want to distribute your VMs across multiple zones in a region in order to protect against zonal failure or to automatically find zones with limited resource like Spot VMs
Create a MIG with autoscaling	You want your MIG to automatically create VMs in the group when demand increases and delete VMs when demand drops
Create a MIG that uses preemptible VMs	Your workload can tolerate disruptions and you want to take advantage of the cost-savings associated with preemptible VMs
Create a MIG with stateful configuration	Your workload needs stateful configuration—for example, you need disks that must retain their data whenever VMs are autohealed, updated, or recreated

Note: By default, Compute Engine creates–and when necessary recreates–each VM in a MIG based on the configuration that you set in the MIG's instance template. The default behavior for all persistent disks in a MIG is to delete or recreate them when the corresponding VM is deleted or recreated, so you should not rely on attached disks as persistent data. To retain your data in a MIG, you can back up the data in another centralized location, such as Cloud Storage, or add configuration for stateful disks.

Limitations

MIGs have different limitations depending on which features you use. The following lists show general MIG limitations as well as additional limitations if you use regional or stateful features.

• By default, you can create up to 1,000 VMs in a zonal MIG. If you need more, use one of the following options:

  • Increase the size limit of your MIG.
  • Create a regional MIG, which allows twice as many VMs as a zonal MIG.
  • Create multiple MIGs and split your workload across them.
  • Contact support to make a request.

• When updating a MIG, you can specify up to 1,000 VMs in a single request.

• Once the MIG is created, you cannot change its networks or subnetworks. All VMs in the MIG are assigned to the same subnetworks.

• Shared VPC on interfaces other than nic0 for managed instance groups is supported in gcloud CLI and the API, but not in Google Cloud console.

A MIG that is spread across multiple zones—a regional MIG—has the following limitations:

• By default, you can create up to 2,000 VMs. If you need more, increase the size limit of your MIG or contact support.
• You must select which zones are associated with a regional MIG when you create the MIG. After you choose specific zones during creation, you cannot change or update the zones later. But you can set the MIG's target distribution shape to specify how the group distributes its managed instances across the zones that you selected.

• If you set the group's target distribution shape to BALANCED, ANY, or ANY_SINGLE_ZONE, review the target distribution shape limitations.

• If you want to autoscale a regional MIG, you must set the group's target distribution shape to BALANCED (preview) or EVEN. To set the target distribution shape to BALANCED, you must disable proactive instance redistribution.

• If you want to use load balancing with a regional MIG, the following limitations apply:

  • You cannot use the maxRate balancing mode.
  • If you use an HTTP(S) load balancing scheme with a regional MIG, you must choose the maxRatePerInstance or maxUtilization balancing mode.

A MIG with stateful configuration—a stateful MIG—has the following limitations:

• You cannot use autoscaling if your MIG has stateful configuration.
• If you want to use automated rolling updates, you must set the replacement method to RECREATE.
• For stateful regional MIGs, you must disable proactive redistribution (set the redistribution type to NONE) to prevent deletion of stateful instances by automatic cross-zone redistribution.
• If you use an all-instances configuration to override instance template properties, you cannot specify those properties in any per-instance configuration and at the same time in the group's all-instances configuration.

If you want to configure an autoscaler for your MIG, review the autoscaler specifications, too.

Additional MIG tasks

After you've created a MIG, you might want to do the following:

Learn about the group and its VMs

• View info about your MIG and its managed VM instances
• Learn what a managed instance is and how to work with managed instances

Resize the group

• Add or remove VMs from the group

  • Automatically resize a MIG based on increases or decreases in load by configuring an autoscaler
  • Manually set the size of a MIG
  • Disable creation retries mode during resize
  • Create instances with specific names in a MIG
  • Delete specific instances from a group
  • Abandon instances from a group

• Increase the group's size limit

• Delete the group

Change the group's VM configuration

• Change the instance template for the group

• Apply configuration updates to the VMs in a MIG

  • Automatically apply configuration updates to VMs in a MIG
  • Selectively apply configuration updates to specific VMs

  • Understand the instanceTemplate and versions fields

  • Recreate instances in the group

  • Canary test a new instance template in a MIG

• Learn how to add stateful configuration in order to preserve disks, IP addresses, and metadata when VMs are recreated

Add MIG features

• Set up an application-based health check to automatically recreate VMs if your application does not respond as expected
• Set up a load balancer to distribute user traffic across multiple instances of your application

Tutorials

Try a tutorial:

• Use autohealing for highly available applications
• Use load balancing for highly available applications
• Use autoscaling for highly scalable applications
• Migrate an existing workload to a stateful managed instance group