An instance group is a collection of virtual machine (VM) instances that you can manage as a single entity.
Compute Engine offers two kinds of VM instance groups, managed and unmanaged:
Managed instance groups (MIGs) let you operate apps on multiple identical VMs. You can make your workloads scalable and highly available by taking advantage of automated MIG services, including: autoscaling, autohealing, regional (multiple zone) deployment, and automatic updating. Unmanaged instance groups let you load balance across a fleet of VMs that you manage yourself.
Managed instance groups (MIGs)
Use a managed instance group (MIG) for scenarios like these:
Stateless serving workloads, such as a website frontend Stateless batch, high-performance, or high-throughput compute workloads, such as image processing from a queue Stateful applications, such as databases, legacy applications, and long-running batch computations with checkpointing Compute Engine maintains each of the MIG's based on the configuration that you specify in an and optional . For information about how to create a MIG, see .
Benefits
MIGs offer the following advantages:
Automatically repairing failed VMs. If a VM in the group stops, crashes, gets preempted (), or is deleted by an action not initiated by the MIG, the MIG automatically recreates that VM based on its original configuration (same VM name, same template) so that the VM can resume its work. Application-based autohealing. You can also set up an application-based health check, which periodically verifies that your application responds as expected on each of the MIG's instances. If an application is not responding on a VM, the MIG automatically recreates that VM for you. Checking that an application responds is more precise than simply verifying that a VM is up and running. Regional (multiple zone) coverage. Regional MIGs let you spread app load across multiple zones. This replication protects against zonal failures. If that happens, your app can continue serving traffic from instances running in the remaining available zones in the same region. Load balancing. MIGs work with load balancing services to distribute traffic across all of the instances in the group. Scalability. When your apps require additional compute resources, autoscaled MIGs can automatically grow the number of instances in the group to meet demand. If demand drops, autoscaled MIGs can automatically shrink to reduce your costs. Automated updates. The MIG automatic updater lets you safely deploy new versions of software to instances in your MIG and supports a flexible range of rollout scenarios, such as rolling updates and canary updates. You can control the speed and scope of deployment as well as the level of disruption to your service. Support for stateful workloads. You can use MIGs for building highly available deployments and automating operation of applications with stateful data or configuration, such as databases, DNS servers, legacy monolith applications, or long-running batch computations with checkpointing. Stateful MIGs preserve each instance's unique state (instance name, attached persistent disks, and metadata) on machine restart, recreation, auto-healing, and update events. Create GPU VMs all at once. When you have a batch job, such as an AI or ML training, that requires an exact number of GPU VMs, then creating a resize request in a MIG can help you to create the VMs all at once. You can specify the duration for which you want the VMs to run for, thereby improving the obtainability of highly-demanded resources such as GPUs.
Overview of MIG capabilities and common workloads
Managed Instance Groups
