Reduce latency by using compact placement policies

This document describes how to reduce network latency among your virtual machine (VM) instances by creating and applying compact placement policies to them.

A compact placement policy specifies that your VMs should be physically placed closer to each other. This can help improve performance and reduce network latency among your VMs when, for example, you run high performance computing (HPC), machine learning (ML), or database server workloads.

Before you begin

If you haven't already, set up authentication. Authentication is the process by which your identity is verified for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine as follows.

Select the tab for how you plan to use the samples on this page:
gcloud
1. Install the Google Cloud CLI, then initialize it by running the following command:
  gcloud init
  Note: If you installed the gcloud CLI previously, make sure you have the latest version by running gcloud components update.
2. Set a default region and zone.
REST

To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.
For more information, see Authenticate for using REST in the Google Cloud authentication documentation.

Required roles

To get the permissions that you need to create and apply a compact placement policy to VMs, ask your administrator to grant you the following IAM roles on your project:

Compute Instance Admin (v1) (roles/compute.instanceAdmin.v1)
To create a reservation: Compute Admin (roles/compute.admin)

For more information about granting roles, see Manage access to projects, folders, and organizations.

These predefined roles contain the permissions required to create and apply a compact placement policy to VMs. To see the exact permissions that are required, expand the Required permissions section:

Required permissions

The following permissions are required to create and apply a compact placement policy to VMs:

To create placement policies: compute.resourcePolicies.create on the project
To apply a placement policy to existing VMs: compute.instances.addResourcePolicies on the project
To create VMs:
- compute.instances.create on the project
- To use a custom image to create the VM: compute.images.useReadOnly on the image
- To use a snapshot to create the VM: compute.snapshots.useReadOnly on the snapshot
- To use an instance template to create the VM: compute.instanceTemplates.useReadOnly on the instance template
- To assign a legacy network to the VM: compute.networks.use on the project
- To specify a static IP address for the VM: compute.addresses.use on the project
- To assign an external IP address to the VM when using a legacy network: compute.networks.useExternalIp on the project
- To specify a subnet for the VM: compute.subnetworks.use on the project or on the chosen subnet
- To assign an external IP address to the VM when using a VPC network: compute.subnetworks.useExternalIp on the project or on the chosen subnet
- To set VM instance metadata for the VM: compute.instances.setMetadata on the project
- To set tags for the VM: compute.instances.setTags on the VM
- To set labels for the VM: compute.instances.setLabels on the VM
- To set a service account for the VM to use: compute.instances.setServiceAccount on the VM
- To create a new disk for the VM: compute.disks.create on the project
- To attach an existing disk in read-only or read-write mode: compute.disks.use on the disk
- To attach an existing disk in read-only mode: compute.disks.useReadOnly on the disk
To create a reservation: compute.reservations.create on the project
To create an instance template: compute.instanceTemplates.create on the project
To create a managed instance group (MIG): compute.instanceGroupManagers.create on the project
To view the details of a VM: compute.instances.get on the project

You might also be able to get these permissions with custom roles or other predefined roles.

Create a compact placement policy

Unless you want to apply a compact placement policy to N2 or N2D VMs, Google Cloud recommends specifying a maximum distance value when creating the policy. For more information, see How compact placement policies work.

To create a compact placement policy, select one of the following options:

gcloud

To apply the compact placement policy to N2 or N2D VMs, create the policy using the gcloud compute resource-policies create group-placement command with the --collocation=collocated flag.
```
gcloud compute resource-policies create group-placement POLICY_NAME \
    --collocation=collocated \
    --region=REGION
```
Replace the following:
- POLICY_NAME: the name of the compact placement policy.
- REGION: the region in which to create the placement policy.
To apply the compact placement policy to any other supported VMs, create the policy using the gcloud beta compute resource-policies create group-placement command with the --collocation=collocated and --max-distance flags.

Preview — The --max-distance flag

This feature is subject to the "Pre-GA Offerings Terms" in the General Service Terms section of the Service Specific Terms. Pre-GA features are available "as is" and might have limited support. For more information, see the launch stage descriptions.
```
gcloud beta compute resource-policies create group-placement POLICY_NAME \
    --collocation=collocated \
    --max-distance=MAX_DISTANCE \
    --region=REGION
```
Replace the following:
- POLICY_NAME: the name of the compact placement policy.
- MAX_DISTANCE: the maximum distance configuration for your VMs. The value must be between 1, which specifies to place your VMs in the same rack for the lowest network latency possible, and 3, which specifies to place your VMs in adjacent clusters. If you want to apply the compact placement policy to a reservation, then you can't specify a value of 1.
- REGION: the region in which to create the placement policy.

REST

To apply the compact placement policy to N2 or N2D VMs, create the policy by making a POST request to the resourcePolicies.insert method. In the request body, include the collocation field and set it to COLLOCATED.
```
POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/regions/REGION/resourcePolicies

{
  "name": "POLICY_NAME",
  "groupPlacementPolicy": {
    "collocation": "COLLOCATED"
  }
}
```
Replace the following:
- PROJECT_ID: the ID of the project where you want to create the placement policy.
- REGION: the region in which to create the placement policy.
- POLICY_NAME: the name of the compact placement policy.
To apply the compact placement policy to any other supported VMs, create the policy by making a POST request to the beta.resourcePolicies.insert method. In the request body, include the following:
- The collocation field set to COLLOCATED.
- The maxDistance field.
Preview — The maxDistance field

This feature is subject to the "Pre-GA Offerings Terms" in the General Service Terms section of the Service Specific Terms. Pre-GA features are available "as is" and might have limited support. For more information, see the launch stage descriptions.
```
POST https://compute.googleapis.com/compute/beta/projects/PROJECT_ID/regions/REGION/resourcePolicies

{
  "name": "POLICY_NAME",
  "groupPlacementPolicy": {
    "collocation": "COLLOCATED",
    "maxDistance": "MAX_DISTANCE"
  }
}
```
Replace the following:
- PROJECT_ID: the ID of the project where you want to create the placement policy.
- REGION: the region in which to create the placement policy.
- POLICY_NAME: the name of the compact placement policy.
- MAX_DISTANCE: the maximum distance configuration for your VMs. The value must be between 1, which specifies to place your VMs in the same rack for the lowest network latency possible, and 3, which specifies to place your VMs in adjacent clusters. If you want to apply the compact placement policy to a reservation, then you can't specify a value of 1.

Apply a compact placement policy

You can apply a compact placement policy to an existing VM or MIG, or when creating VMs, instance templates, MIGs, or reservations of VMs.

To apply a compact placement policy to a Compute Engine resource, select one of the following methods:

Apply the policy to an existing VM.
Apply the policy while creating a VM.
Apply the policy while creating VMs in bulk.
Apply the policy while creating a reservation.
Apply the policy while creating an instance template.
Apply the policy to VMs in a MIG.

After you apply a compact placement policy to a VM, you can verify the physical location of the VM in relation to other VMs that specify the same placement policy.

Apply the policy to an existing VM

Before applying a compact placement policy to an existing VM, make sure of the following:

The VM and the compact placement policy must be located in the same region. For example, if the placement policy is located in region us-central1, then the VM must be located in a zone in us-central1. If you need to migrate a VM to another region, then see Move a VM between zones or regions.
The VM must use a supported machine series and host maintenance policy. If you need to make changes to the VM, then do one or both of the following:
- Change the machine type of the VM.
- Update the host maintenance policy of the VM.

Otherwise, applying the compact placement policy to the VM fails. If the VM already specifies a placement policy and you want to replace it, then see Replace a placement policy in a VM instead.

To apply a compact placement policy to an existing VM, select one of the following options:

gcloud

Stop the VM.
To apply a compact placement policy to an existing VM, use the gcloud compute instances add-resource-policies command.
```
gcloud compute instances add-resource-policies VM_NAME \
    --resource-policies=POLICY_NAME \
    --zone=ZONE
```
Replace the following:
- VM_NAME: the name of an existing VM.
- POLICY_NAME: the name of an existing compact placement policy.
- ZONE: the zone where the VM is located.
Restart the VM.

REST

Stop the VM.
To apply a compact placement policy to an existing VM, make a POST request to the instances.addResourcePolicies method.
```
POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/VM_NAME/addResourcePolicies

{
  "resourcePolicies": [
    "projects/PROJECT_ID/regions/REGION/resourcePolicies/POLICY_NAME"
  ]
}
```
Replace the following:
- PROJECT_ID: the ID of the project where the compact placement policy and the VM are located.
- ZONE: the zone where the VM is located.
- VM_NAME: the name of an existing VM.
- REGION: the region where the compact placement policy is located.
- POLICY_NAME: the name of an existing compact placement policy.
Restart the VM.

Apply the policy while creating a VM

You can only create a VM that specifies a compact placement policy in the same region as the placement policy.

To create a VM that specifies a compact placement policy, select one of the following options:

gcloud

To create a VM that specifies a compact placement policy, use the gcloud compute instances create command with the --maintenance-policy and --resource-policies flags.

gcloud compute instances create VM_NAME \
    --machine-type=MACHINE_TYPE \
    --maintenance-policy=MAINTENANCE_POLICY \
    --resource-policies=POLICY_NAME \
    --zone=ZONE

Replace the following:

VM_NAME: the name of the VM to create.
MACHINE_TYPE: a supported machine type for compact placement policies.
MAINTENANCE_POLICY: the host maintenance policy of the VM. If the compact placement policy you specify uses a maximum distance value of 1 or 2, then you can only specify TERMINATE. Otherwise, you can specify either MIGRATE or TERMINATE.
POLICY_NAME: the name of an existing compact placement policy.
ZONE: the zone in which to create the VM.

REST

To create a VM that specifies a compact placement policy, make a POST request to the instances.insert method. In the request body, include the onHostMaintenance and resourcePolicies fields.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances

{
  "name": "VM_NAME",
  "machineType": "zones/ZONE/machineTypes/MACHINE_TYPE",
  "disks": [
    {
      "boot": true,
      "initializeParams": {
        "sourceImage": "projects/IMAGE_PROJECT/global/images/IMAGE"
      }
    }
  ],
  "networkInterfaces": [
    {
      "network": "global/networks/default"
    }
  ],
  "resourcePolicies": [
    "projects/PROJECT_ID/regions/REGION/resourcePolicies/POLICY_NAME"
  ],
  "scheduling": {
    "onHostMaintenance": "MAINTENANCE_POLICY"
  }
}

Replace the following:

PROJECT_ID: the ID of the project where the compact placement policy is located.
ZONE: the zone where to create the VM in and where the machine type is located. You can only specify a zone within the region of the compact placement policy.
VM_NAME: the name of the VM to create.
MACHINE_TYPE: a supported machine type for compact placement policies.
IMAGE_PROJECT: the image project that contains the image—for example, debian-cloud. For more information about the supported image projects, see Public images.
IMAGE: specify one of the following:
- A specific version of the OS image—for example, debian-12-bookworm-v20240617.
- An image family, which must be formatted as family/IMAGE_FAMILY. This specifies the most recent, non-deprecated OS image. For example, if you specify family/debian-12, the latest version in the Debian 12 image family is used. For more information about using image families, see Image families best practices.
REGION: the region where the compact placement policy is located.
POLICY_NAME: the name of an existing compact placement policy.
MAINTENANCE_POLICY: the host maintenance policy of the VM. If the compact placement policy you specify uses a maximum distance value of 1 or 2, you can only specify TERMINATE. Otherwise, you can specify either MIGRATE or TERMINATE.

For more information about the configuration options to create a VM, see Create and start a VM instance.

Apply the policy while creating VMs in bulk

You can only create VMs in bulk with a compact placement policy in the same region as the placement policy.

To create VMs in bulk that specify a compact placement policy, select one of the following options:

gcloud

To create VMs in bulk that specify a compact placement policy, use the gcloud compute instances bulk create command with the --maintenance-policy and --resource-policies flags.

For example, to create VMs in bulk in a single zone and specify a name pattern for the VMs, run the following command:

gcloud compute instances bulk create \
    --count=COUNT \
    --machine-type=MACHINE_TYPE \
    --maintenance-policy=MAINTENANCE_POLICY \
    --name-pattern=NAME_PATTERN \
    --resource-policies=POLICY_NAME \
    --zone=ZONE

Replace the following:

COUNT: the number of VMs to create, which can't be higher than the supported maximum number of VMs of the specified compact placement policy.
MACHINE_TYPE: a supported machine type for compact placement policies.
MAINTENANCE_POLICY: the host maintenance policy of the VM. If the compact placement policy you specify uses a maximum distance value of 1 or 2, then you can only specify TERMINATE. Otherwise, you can specify either MIGRATE or TERMINATE.
NAME_PATTERN: the name pattern for the VMs. To replace a sequence of numbers in a VM name, use a sequence of hash (#) characters. For example, using vm-# for the name pattern generates VMs with names starting with vm-1, vm-2, and continuing up to the number of VMs specified by COUNT.
POLICY_NAME: the name of an existing compact placement policy.
ZONE: the zone in which to create the VMs in bulk.

REST

To create VMs in bulk that specify a compact placement policy, make a POST request to the instances.bulkInsert method. In the request body, include the onHostMaintenance and resourcePolicies fields.

For example, to create VMs in bulk in a single zone and specify a name pattern for the VMs, make a POST request as follows:

POST https://www.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/bulkInsert

{
  "count": "COUNT",
  "namePattern": "NAME_PATTERN",
  "instanceProperties": {
    "machineType": "MACHINE_TYPE",
    "disks": [
      {
        "boot": true,
        "initializeParams": {
          "sourceImage": "projects/IMAGE_PROJECT/global/images/IMAGE"
        }
      }
    ],
    "networkInterfaces": [
      {
        "network": "global/networks/default"
      }
    ],
    "resourcePolicies": [
      "projects/PROJECT_ID/regions/REGION/resourcePolicies/POLICY_NAME"
    ],
    "scheduling": {
      "onHostMaintenance": "MAINTENANCE_POLICY"
    }
  }
}

Replace the following:

PROJECT_ID: the ID of the project where the compact placement policy is located.
ZONE: the zone in which to create the VMs in bulk.
COUNT: the number of VMs to create, which can't be higher than the supported maximum number of VMs of the specified compact placement policy.
NAME_PATTERN: the name pattern for the VMs. To replace a sequence of numbers in a VM name, use a sequence of hash (#) characters. For example, using vm-# for the name pattern generates VMs with names starting with vm-1, vm-2, and continuing up to the number of VMs specified by COUNT.
```
    with names starting with `vm-1`, `vm-2`, and continuing up to the number
```
of VMs specified by COUNT.
MACHINE_TYPE: a supported machine type for compact placement policies.
IMAGE_PROJECT: the image project that contains the image—for example, debian-cloud. For more information about the supported image projects, see Public images.
IMAGE: specify one of the following:
- A specific version of the OS image—for example, debian-12-bookworm-v20240617.
- An image family, which must be formatted as family/IMAGE_FAMILY. This specifies the most recent, non-deprecated OS image. For example, if you specify family/debian-12, the latest version in the Debian 12 image family is used. For more information about using image families, see Image families best practices.
REGION: the region where the compact placement policy is located.
POLICY_NAME: the name of an existing compact placement policy.
MAINTENANCE_POLICY: the host maintenance policy of the VM. If the compact placement policy you specify uses a maximum distance value of 1 or 2, you can only specify TERMINATE. Otherwise, you can specify either MIGRATE or TERMINATE.

For more information about the configuration options to create VMs in bulk, see Create VMs in bulk.

Apply the policy while creating a reservation

If you want to create an on-demand, single-project reservation that specifies a compact placement policy, then you must create a specifically targeted reservation. When you create VMs to consume the reservation, make sure of the following:

The VMs must specify the same compact placement policy applied to the reservation.
The VMs must specifically target the reservation to consume it. For more information, see Consume VMs from a specific reservation.

To create a single-project reservation with a compact placement policy, select one of the following methods:

Create the reservation by specifying properties directly as described in this section.
Apply the policy while creating an instance template as described in this document, and then create a single-project reservation by specifying the newly created instance template.

To create a single-project reservation with a compact placement policy by specifying properties directly, select one of the following options:

gcloud

To create a single-project reservation with a compact placement policy by specifying properties directly, use the gcloud compute reservations create command with the --require-specific-reservation and --resource-policies=policy flags.

gcloud compute reservations create RESERVATION_NAME \
    --machine-type=MACHINE_TYPE \
    --require-specific-reservation \
    --resource-policies=policy=POLICY_NAME \
    --vm-count=NUMBER_OF_VMS \
    --zone=ZONE

Replace the following:

RESERVATION_NAME: the name of the reservation.
MACHINE_TYPE: a supported machine type for compact placement policies.
POLICY_NAME: the name of an existing compact placement policy.
NUMBER_OF_VMS: the number of VMs to reserve, which can't be higher than the supported maximum number of VMs of the specified compact placement policy.
ZONE: the zone in which to reserve VMs. You can only reserve VMs in a zone within the region of the specified compact placement policy.

REST

To create a single-project reservation with a compact placement policy by specifying properties directly, make a POST request to the reservations.insert method. In the request body, include the resourcePolicies field, and the specificReservationRequired field set to true.

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/reservations

{
  "name": "RESERVATION_NAME",
  "resourcePolicies": {
    "policy" : "projects/PROJECT_ID/regions/REGION/resourcePolicies/POLICY_NAME"
  },
  "specificReservation": {
    "count": "NUMBER_OF_VMS",
    "instanceProperties": {
      "machineType": "MACHINE_TYPE",
    }
  },
  "specificReservationRequired": true
}

Replace the following:

PROJECT_ID: the ID of the project where the compact placement policy is located.
ZONE: the zone in which to reserve VMs. You can only reserve VMs in a zone within the region of the specified compact placement policy.
RESERVATION_NAME: the name of the reservation.
REGION: the region where the compact placement policy is located.
POLICY_NAME: the name of an existing compact placement policy.
NUMBER_OF_VMS: the number of VMs to reserve, which can't be higher than the supported maximum number of VMs of the specified compact placement policy.
MACHINE_TYPE: a supported machine type for compact placement policies.

For more information about the configuration options to create single-project reservations, see Create a reservation for a single project.

Apply the policy while creating an instance template

If you want to create a regional instance template, then you must create the template in the same region as the compact placement policy. Otherwise, creating the instance template fails.

After creating an instance template that specifies a compact placement policy, you can use the template to do the following:

To create an instance template that specifies a compact placement policy, select one of the following options:

gcloud

To create an instance template that specifies a compact placement policy, use the gcloud compute instance-templates create command with the --maintenance-policy and --resource-policies flags.

For example, to create a global instance template that specifies a compact placement policy, run the following command:

gcloud compute instance-templates create INSTANCE_TEMPLATE_NAME \
    --machine-type=MACHINE_TYPE \
    --maintenance-policy=MAINTENANCE_POLICY \
    --resource-policies=POLICY_NAME

Replace the following:

INSTANCE_TEMPLATE_NAME: the name of the instance template.
MACHINE_TYPE: a supported machine type for compact placement policies.
MAINTENANCE_POLICY: the host maintenance policy of the VM. If the compact placement policy you specify uses a maximum distance value of 1 or 2, then you can only specify TERMINATE. Otherwise, you can specify either MIGRATE or TERMINATE.
POLICY_NAME: the name of an existing compact placement policy.

REST

To create an instance template that specifies a compact placement policy, make a POST request to one of the following methods:

To create a global instance template: instanceTemplates.insert method.
To create a regional instance template: regionInstanceTemplates.insert method.

In the request body, include the onHostMaintenance and resourcePolicies fields.

For example, to create a global instance template that specifies a compact placement policy, make a POST request as follows:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/global/instanceTemplates

{
  "name": "INSTANCE_TEMPLATE_NAME",
  "properties": {
    "disks": [
      {
        "boot": true,
        "initializeParams": {
          "sourceImage": "projects/IMAGE_PROJECT/global/images/IMAGE"
        }
      }
    ],
    "machineType": "MACHINE_TYPE",
    "networkInterfaces": [
      {
        "network": "global/networks/default"
      }
    ],
    "resourcePolicies": [
      "POLICY_NAME"
    ],
    "scheduling": {
      "onHostMaintenance": "MAINTENANCE_POLICY"
    }
  }
}

Replace the following:

PROJECT_ID: the ID of the project where the compact placement policy is located.
INSTANCE_TEMPLATE_NAME: the name of the instance template.
IMAGE_PROJECT: the image project that contains the image—for example, debian-cloud. For more information about the supported image projects, see Public images.
IMAGE: specify one of the following:
- A specific version of the OS image—for example, debian-12-bookworm-v20240617.
- An image family, which must be formatted as family/IMAGE_FAMILY. This specifies the most recent, non-deprecated OS image. For example, if you specify family/debian-12, the latest version in the Debian 12 image family is used. For more information about using image families, see Image families best practices.
MACHINE_TYPE: a supported machine type for compact placement policies.
POLICY_NAME: the name of an existing compact placement policy.
MAINTENANCE_POLICY: the host maintenance policy of the VM. If the compact placement policy you specify uses a maximum distance value of 1 or 2, then you can only specify TERMINATE. Otherwise, you can specify either MIGRATE or TERMINATE.

For more information about the configuration options to create an instance template, see Create instance templates.

Apply the policy to VMs in a MIG

After you create an instance template that specifies a compact placement policy, you can use the template to do the following:

Apply the policy while creating a MIG.
Apply the policy to an existing MIG.

Apply the policy while creating a MIG

You can only create VMs that specify a compact placement policy if the VMs are located in the same region as the placement policy.

To create a MIG using an instance template that specifies a compact placement policy, select one of the following options:

gcloud

To create a MIG using an instance template that specifies a compact placement policy, use the gcloud compute instance-groups managed create command.

For example, to create a zonal MIG using a global instance template that specifies a compact placement policy, run the following command:

gcloud compute instance-groups managed create INSTANCE_GROUP_NAME \
    --size=SIZE \
    --template=INSTANCE_TEMPLATE_NAME \
    --zone=ZONE

Replace the following:

INSTANCE_GROUP_NAME: the name of the MIG to create.
SIZE: the size of the MIG.
INSTANCE_TEMPLATE_NAME: the name of an existing global instance template that specifies a compact placement policy.
ZONE: the zone in which to create the MIG, which must be within the region where the compact placement policy is located.

REST

To create a MIG using an instance template that specifies a compact placement policy, make a POST request to one of the following methods:

To create a zonal MIG: instanceGroupManagers.insert method.
To create a regional MIG: regionInstanceGroupManagers.insert method.

For example, to create a zonal MIG using a global instance template that specifies a compact placement policy, make a POST request as follows:

POST https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instanceGroupManagers

{
  "name": "INSTANCE_GROUP_NAME",
  "targetSize": SIZE,
  "versions": [
    {
      "instanceTemplate": "global/instanceTemplates/INSTANCE_TEMPLATE_NAME"
    }
  ]
}

Replace the following:

PROJECT_ID: the ID of the project where the compact placement policy and the instance template that specifies the placement policy are located.
ZONE: the zone in which to create the MIG, which must be within the region where the compact placement policy is located.
INSTANCE_GROUP_NAME: the name of the MIG to create.
INSTANCE_TEMPLATE_NAME: the name of an existing global instance template that specifies a compact placement policy.
SIZE: the size of the MIG.

For more information about the configuration options to create MIGs, see Basic scenarios for creating MIGs.

Apply the policy to an existing MIG

You can only apply a compact placement policy to an existing MIG if the MIG is located in the same region as the placement policy or, for zonal MIGs, in a zone within the same region as the placement policy.

To update a MIG to use an instance template that specifies a compact placement policy, select one of the following options:

gcloud

To update a MIG to use an instance template that specifies a compact placement policy, use the gcloud compute instance-groups managed rolling-action start-update command.

For example, to update a zonal MIG to use an instance template that specifies a compact placement policy, and replace the existing VMs from the MIG with new VMs that specify the template's properties, run the following command:

gcloud compute instance-groups managed rolling-action start-update MIG_NAME \
    --version=template=INSTANCE_TEMPLATE_NAME \
    --zone=ZONE

Replace the following:

MIG_NAME: the name of an existing MIG.
INSTANCE_TEMPLATE_NAME: the name of an existing global instance template that specifies a compact placement policy.
ZONE: the zone where the MIG is located. You can only apply the compact placement policy to a MIG located within the same region as the placement policy.

REST

To update a MIG to use an instance template that specifies a compact placement policy, and automatically apply the properties of the template and the placement policy to existing VMs in the MIG, make a PATCH request to one of the following methods:

To update a zonal MIG: instanceGroupManagers.insert method.
To update a regional MIG: regionInstanceGroupManagers.insert method.

For example, to update a zonal MIG to use a global instance template that specifies a compact placement policy, and replace the existing VMs from the MIG with new VMs that specify the template's properties, make the following PATCH request:

PATCH https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instanceGroupManagers/MIG_NAME

{
  "instanceTemplate": "global/instanceTemplates/INSTANCE_TEMPLATE_NAME"
}

Replace the following:

PROJECT_ID: the ID of the project where the MIG, the compact placement policy, and the instance template that specifies the placement policy are located.
ZONE: the zone where the MIG is located. You can only apply the compact placement policy to a MIG located within the same region as the placement policy.
MIG_NAME: the name of an existing MIG.
INSTANCE_TEMPLATE_NAME: the name of an existing global instance template that specifies a compact placement policy.

For more information about the configuration options to update the VMs in a MIG, see Update and apply new configurations to VMs in a MIG.

Verify the physical location of a VM

After you apply a compact placement policy to a VM, you can view how the compact placement policy affected its physical location in relation to other VMs that specify the same policy. This helps you determine if the compact placement policy was correctly applied to a VM and map which VMs are the closest to each other.

To verify the physical location of a VM that specifies a placement policy in relation to other VMs, select one of the following options:

gcloud

To view the physical location of a VM that specifies a compact placement policy, use the gcloud compute instances describe command with the --format flag.

gcloud compute instances describe VM_NAME \
    --format="table[box,title=VM-Position](resourcePolicies.scope():sort=1,resourceStatus.physicalHost:label=location)" \
    --zone=ZONE

Replace the following:

VM_NAME: the name of an existing VM.
ZONE: the zone where the VM is located.

The output is similar to the following:

VM-Position

RESOURCE_POLICIES: us-central1/resourcePolicies/example-policy']
PHYSICAL_HOST: /CCCCCCC/BBBBBB/AAAA

The value for the PHYSICAL_HOST field is composed by three parts. These parts each represent the cluster, rack, and host where the VM is located.

When comparing the position of two VMs that specify the same compact placement policy, the more parts in the PHYSICAL_HOST field the VMs share, the closer they are located to each other. For example, if two VMs both specify one of the following sample values for the PHYSICAL_HOST field:

/CCCCCCC/xxxxxx/xxxx: the two VMs are placed in the same cluster, which equals a maximum distance value of 2. VMs placed in the same cluster experience low network latency.
/CCCCCCC/BBBBBB/xxxx: the two VMs are placed in the same rack, which equals a maximum distance value of 1. VMs placed in the same rack experience lower network latency than VMs placed in the same cluster.
/CCCCCCC/BBBBBB/AAAA: the two VMs share the same host. VMs placed in the same host minimize network latency as much as possible.

REST

To view the physical location of a VM that specifies a compact placement policy, make a GET request to the instances.get method.

GET https://compute.googleapis.com/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/VM_NAME

Replace the following:

PROJECT_ID: the ID of the project where the VM is located.
ZONE: the zone where the VM is located.
VM_NAME: the name of an existing VM that specifies a placement policy.

The output is similar to the following:

{
  ...
  "resourcePolicies": [
    "https://www.googleapis.com/compute/v1/projects/example-project/regions/us-central1/resourcePolicies/example-policy"
  ],
  "resourceStatus": {
    "physicalHost": "/xxxxxxxx/xxxxxx/xxxxx"
  },
  ...
}

The value for the physicalHost field is composed by three parts. These parts each represent the cluster, rack, and host where the VM is located.

When comparing the position of two VMs that specify the same compact placement policy, the more parts in the physicalHost field the VMs share, the closer they are located to each other. For example, if two VMs both specify one of the following sample values for the physicalHost field:

/CCCCCCC/xxxxxx/xxxx: the two VMs are placed in the same cluster, which equals a maximum distance value of 2. VMs placed in the same cluster experience low network latency.
/CCCCCCC/BBBBBB/xxxx: the two VMs are placed in the same rack, which equals a maximum distance value of 1. VMs placed in the same rack experience lower network latency than VMs placed in the same cluster.
/CCCCCCC/BBBBBB/AAAA: the two VMs share the same host. VMs placed in the same host minimize network latency as much as possible.

What's next?

Learn how to view placement policies.
Learn how to replace, remove, or delete placement policies.
Learn how to do the following with a VM that specifies a placement policy:
- View the status of the VM.
- Connect to the VM.