AWS Placement Group

The AWS placement group customization allows the user to specify placement groups for control-plane and worker machines to control their placement strategy within AWS.

This customization will be available when the provider-specific cluster configuration patch is included in the ClusterClass.

What are Placement Groups?

AWS placement groups are logical groupings of instances within a single Availability Zone that influence how instances are placed on underlying hardware. They are useful for:

• Cluster Placement Groups: For applications that benefit from low network latency, high network throughput, or both
• Partition Placement Groups: For large distributed and replicated workloads, such as HDFS, HBase, and Cassandra
• Spread Placement Groups: For applications that have a small number of critical instances that should be kept separate

Configuration

The placement group configuration supports the following field:

Examples

Control Plane and Worker Placement Groups

To specify placement groups for both control plane and worker machines:

apiVersion: cluster.x-k8s.io/v1beta1
kind: Cluster
metadata:
  name: <NAME>
spec:
  topology:
    variables:
      - name: clusterConfig
        value:
          controlPlane:
            aws:
              placementGroup:
                name: "control-plane-pg"
      - name: workerConfig
        value:
          aws:
            placementGroup:
              name: "worker-pg"

Control Plane Only

To specify placement group only for control plane machines:

apiVersion: cluster.x-k8s.io/v1beta1
kind: Cluster
metadata:
  name: <NAME>
spec:
  topology:
    variables:
      - name: clusterConfig
        value:
          controlPlane:
            aws:
              placementGroup:
                name: "control-plane-pg"

MachineDeployment Overrides

You can customize individual MachineDeployments by using the overrides field:

spec:
  topology:
    # ...
    workers:
      machineDeployments:
        - class: default-worker
          name: md-0
          variables:
            overrides:
              - name: workerConfig
                value:
                  aws:
                    placementGroup:
                      name: "special-worker-pg"

Resulting CAPA Configuration

Applying the placement group configuration will result in the following value being set:

• control-plane AWSMachineTemplate:

  • spec:
      template:
        spec:
          placementGroupName: control-plane-pg
    

• worker AWSMachineTemplate:

  • spec:
      template:
        spec:
          placementGroupName: worker-pg
    

Best Practices

1. Placement Group Types: Choose the appropriate placement group type based on your workload:

   • Cluster: For applications requiring low latency and high throughput
   • Partition: For large distributed workloads that need fault isolation
   • Spread: For critical instances that need maximum availability

2. Naming Convention: Use descriptive names that indicate the purpose and type of the placement group

3. Availability Zone: Placement groups are constrained to a single Availability Zone, so plan your cluster topology accordingly

4. Instance Types: Some instance types have restrictions on placement groups (e.g., some bare metal instances)

5. Capacity Planning: Consider the placement group capacity limits when designing your cluster

Important Notes

• Placement groups must be created in AWS before they can be referenced
• Placement groups are constrained to a single Availability Zone
• You cannot move an existing instance into a placement group
• Some instance types cannot be launched in placement groups
• Placement groups have capacity limits that vary by type and instance family