google_compute_region_instance_group

A google_compute_region_instance_group_manager runs a fleet of identical VMs spread across multiple zones in a region, the regional variant of a managed instance group, providing zonal resilience. Like any MIG, the manager itself is free; it bills as the Compute Engine instances it runs: target_size × the instance template's machine-type rate. Three e2-medium instances (~$0.0335/hour each) is ~$73.37/month, plus boot disks.

The regional aspect doesn't change the per-instance price, it distributes the same instances across zones for availability. So the cost mechanics match a zonal MIG: you pay for the VMs, and the autoscaler varies target_size with demand. The benefit of regional is that a single-zone outage doesn't take down the whole group.

The levers are the standard VM-fleet ones: attach an autoscaler so target_size tracks demand rather than a fixed peak, use Spot VMs in the template for fault-tolerant workers (60-91% off), right-size the machine type, and apply committed-use discounts to the steady baseline.

c3x prices the regional MIG from the template's machine type and target_size, so the fleet cost is visible before deployment.

Terraform example

A minimal but realistic configuration that C3X can estimate.

resource "google_compute_region_instance_group_manager" "workers" {
  name               = "regional-worker-mig"
  base_instance_name = "worker"
  region             = "us-central1"
  target_size        = 3

  version {
    instance_template = google_compute_instance_template.worker.id
  }

  distribution_policy_zones = ["us-central1-a", "us-central1-b", "us-central1-c"]
}

Pricing dimensions

What you actually pay for when you provision google_compute_region_instance_group_manager.

Dimension	Unit	What's being charged
Instances	per instance-hour	target_size × the instance template's machine-type rate, spread across zones, billed continuously. An autoscaler varies target_size. $0.0335/instance-hour for e2-medium → 3 instances ≈ $73.37/month
Boot disks	per GB-month	Each instance's boot disk bills separately.

Sample C3X output

Three e2-medium instances across zones (fixed target_size), 24/7:

google_compute_region_instance_group_manager.workers
└─ Instances (e2-medium × 3)   2190 instance-hours   $73.37
                               Monthly               $73.37

Optimization tips

Common ways to reduce google_compute_region_instance_group_manager cost without changing the workload.

Attach an autoscaler

Often 30 to 50% on variable load

A regional MIG pinned at a fixed target_size pays for that capacity 24/7. A regional autoscaler grows/shrinks the fleet with demand, so you pay for instances only when load needs them.

Use Spot VMs in the template for fault-tolerant workers

Up to ~91% on Spot instances

Set the instance template to Spot for stateless workers, 60-91% below on-demand. Regional distribution plus Spot gives both zonal resilience and deep savings for interruptible work.

Right-size machine type and apply CUDs

37 to 55% on the baseline

Match the template's machine type to the workload, and cover the steady baseline with committed-use discounts (1-3 year) for 37-55% off; sustained-use discounts apply automatically on top.

FAQ

How is a regional MIG billed?

As the Compute Engine instances it runs, target_size × the template's machine-type rate, plus boot disks, spread across zones. The manager is free. Three e2-medium instances is ~$73/month. The regional aspect adds zonal resilience, not per-instance cost.

Does regional cost more than a zonal MIG?

Not per instance, the same VMs at the same rate, just distributed across zones for availability. You pay for target_size instances either way; regional protects against a single-zone outage.

How does c3x estimate the cost?

From the instance template's machine type and target_size, pricing instance-hours. Autoscaling means actual cost tracks the running count; the estimate reflects the configured target size.

Related resources

Google Cloud

google_compute_instance_group_manager

The zonal MIG variant; same per-instance pricing

`google_compute_region_instance_group_manager` cost estimation