Reduce latency by using compact placement policies

This document describes how to reduce network latency among your Compute Engine instances by creating and applying compact placement policies to them. To learn more about placement policies, including their supported machine series, restrictions, and pricing, see Placement policies overview.

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

Before you begin

  • If you haven't already, then set up authentication. Authentication is the process by which your identity is verified for access to Trusted Cloud by S3NS services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:

    Select the tab for how you plan to use the samples on this page:

    gcloud

    1. Install the Google Cloud CLI, and then sign in to the gcloud CLI with your federated identity. After signing in, initialize the Google Cloud CLI by running the following command: 

      gcloud init
    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.

      Install the Google Cloud CLI, and then sign in to the gcloud CLI with your federated identity. After signing in, initialize the Google Cloud CLI by running the following command: 

      gcloud init

    For more information, see Authenticate for using REST in the Trusted Cloud authentication documentation.

Required roles

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

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 compute instances. 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 compute instances:

  • To create placement policies: compute.resourcePolicies.create on the project
  • To apply a placement policy to existing instances: compute.instances.addResourcePolicies on the project
  • To create instances:
    • 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 instance: 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

Before you create a compact placement policy, consider the following:

  • If you want to apply a compact placement policy to a compute instance other than N2 or N2D, then we recommend that you specify a maximum distance value.

  • You can only apply compact placement policies to A4 or A3 Ultra instances that are deployed using the features provided by Cluster Director. For more information, see Cluster Director in the AI Hypercomputer documentation.

  • By default, you can't apply compact placement policies with a max distance value to A3 Mega, A3 High, or A3 Edge instances. To request access to this feature, contact your assigned Technical Account Manager (TAM) or the Sales team.

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

gcloud

  • To apply the compact placement policy to N2 or N2D instances, 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 instances, create the policy using the gcloud beta compute resource-policies create group-placement command with the --collocation=collocated and --max-distance flags.

    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 instances. The value must be between 1, which specifies to place your instances in the same rack for the lowest network latency possible, and 3, which specifies to place your instances in adjacent clusters. If you want to apply the compact placement policy to a reservation, or to an A4 or A3 Ultra instance, 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 instances, 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.s3nsapis.fr/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 instances, 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.

    POST https://compute.s3nsapis.fr/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 instances. The value must be between 1, which specifies to place your instances in the same rack for the lowest network latency possible, and 3, which specifies to place your instances in adjacent clusters. If you want to apply the compact placement policy to a reservation, or to an A4 or A3 Ultra instance, then you can't specify a value of 1.

Apply a compact placement policy

You can apply a compact placement policy to an existing compute instance or managed instance group (MIG), or when creating instances, instance templates, MIGs, or reservations of instances.

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

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

Apply the policy to an existing instance

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

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

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

gcloud

  1. Stop the instance.

  2. To apply a compact placement policy to an existing instance, use the gcloud compute instances add-resource-policies command.

    gcloud compute instances add-resource-policies INSTANCE_NAME \
    --resource-policies=POLICY_NAME \
    --zone=ZONE

    Replace the following:

    • INSTANCE_NAME: the name of an existing instance.

    • POLICY_NAME: the name of an existing compact placement policy.

    • ZONE: the zone where the instance is located.

  3. Restart the instance.

REST

  1. Stop the instance.

  2. To apply a compact placement policy to an existing instance, make a POST request to the instances.addResourcePolicies method.

    POST https://compute.s3nsapis.fr/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/INSTANCE_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 instance are located.

    • ZONE: the zone where the instance is located.

    • INSTANCE_NAME: the name of an existing instance.

    • REGION: the region where the compact placement policy is located.

    • POLICY_NAME: the name of an existing compact placement policy.

  3. Restart the instance.

Apply the policy while creating a instance

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

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

gcloud

To create a instance 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 INSTANCE_NAME \
    --machine-type=MACHINE_TYPE \
    --maintenance-policy=MAINTENANCE_POLICY \
    --resource-policies=POLICY_NAME \
    --zone=ZONE

Replace the following:

  • INSTANCE_NAME: the name of the instance to create.

  • MACHINE_TYPE: a supported machine type for compact placement policies.

  • MAINTENANCE_POLICY: the host maintenance policy of the instance. If the compact placement policy you specify uses a maximum distance value of 1 or 2, or your chosen machine type doesn't support live migration, then you can only specify TERMINATE. Otherwise, you can specify MIGRATE or TERMINATE.

  • POLICY_NAME: the name of an existing compact placement policy.

  • ZONE: the zone in which to create the instance.

REST

To create an instance 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.s3nsapis.fr/compute/v1/projects/PROJECT_ID/zones/ZONE/instances

{
  "name": "INSTANCE_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 instance in and where the machine type is located. You can only specify a zone in the region of the compact placement policy.

  • INSTANCE_NAME: the name of the instance 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 instance. If the compact placement policy you specify uses a maximum distance value of 1 or 2, or your chosen machine type doesn't support live migration, then you can only specify TERMINATE. Otherwise, you can specify MIGRATE or TERMINATE.

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

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 instances to consume the reservation, make sure of the following:

  • The instances must specify the same compact placement policy applied to the reservation.

  • The instances must specifically target the reservation to consume it. For more information, see Consume instances from a specific reservation.

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

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_INSTANCES \
    --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_INSTANCES: the number of instances to reserve, which can't be higher than the supported maximum number of instances of the specified compact placement policy.

  • ZONE: the zone in which to reserve instances. You can only reserve instances in a zone in 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.s3nsapis.fr/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_INSTANCES",
    "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 instances. You can only reserve instances in a zone in 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_INSTANCES: the number of instances to reserve, which can't be higher than the supported maximum number of instances 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 instance. If the compact placement policy you specify uses a maximum distance value of 1 or 2, or your chosen machine type doesn't support live migration, then you can only specify TERMINATE. Otherwise, you can specify 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:

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.s3nsapis.fr/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 instance. If the compact placement policy you specify uses a maximum distance value of 1 or 2, or your chosen machine type doesn't support live migration, then you can only specify TERMINATE. Otherwise, you can specify MIGRATE or TERMINATE.

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

Apply the policy to instances 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

You can only create compute instances that specify a compact placement policy if the instances 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 in 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:

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.s3nsapis.fr/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 in 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 in 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 instances from the MIG with new instances 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 in 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 instances in the MIG, make a PATCH request to one of the following methods:

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

PATCH https://compute.s3nsapis.fr/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 in 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 instances in a MIG, see Update and apply new configurations to instances in a MIG.

Verify the physical location of an instance

After applying a compact placement policy to a compute instance, you can view the instance's physical location in relation to other instances. This comparison is limited to instances located in your project and that specify the same compact placement policy. Viewing the physical location of an instance helps you to do the following:

  • Confirm that the policy was successfully applied.

  • Identify which instances are closest to each other.

To view the physical location of an instance in relation to other instances that specify the same compact placement policy, select one of the following options:

gcloud

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

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

Replace the following:

  • INSTANCE_NAME: the name of an existing instance that specifies a compact placement policy.

  • ZONE: the zone where the instance 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 instance is located.

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

  • /CCCCCCC/xxxxxx/xxxx: the two instances are placed in the same cluster, which equals a maximum distance value of 2. Instances placed in the same cluster experience low network latency.

  • /CCCCCCC/BBBBBB/xxxx: the two instances are placed in the same rack, which equals a maximum distance value of 1. Instances placed in the same rack experience lower network latency than instances placed in the same cluster.

  • /CCCCCCC/BBBBBB/AAAA: the two instances share the same host. Instances placed in the same host minimize network latency as much as possible.

REST

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

GET https://compute.s3nsapis.fr/compute/v1/projects/PROJECT_ID/zones/ZONE/instances/INSTANCE_NAME

Replace the following:

  • PROJECT_ID: the ID of the project where the instance is located.

  • ZONE: the zone where the instance is located.

  • INSTANCE_NAME: the name of an existing instance that specifies a compact placement policy.

The output is similar to the following:

{
  ...
  "resourcePolicies": [
    "https://www.s3nsapis.fr/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 instance is located.

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

  • /CCCCCCC/xxxxxx/xxxx: the two instances are placed in the same cluster, which equals a maximum distance value of 2. Instances placed in the same cluster experience low network latency.

  • /CCCCCCC/BBBBBB/xxxx: the two instances are placed in the same rack, which equals a maximum distance value of 1. Instances placed in the same rack experience lower network latency than instances placed in the same cluster.

  • /CCCCCCC/BBBBBB/AAAA: the two instances share the same host. Instances placed in the same host minimize network latency as much as possible.

What's next?