Create and use VolumePlacementStrategies

This topic explains how to create and apply a VolumePlacementStrategy custom resource (CR) in your cluster. You can use this strategy to influence the placement of volumes created by Portworx for specific workloads.
For more information on Volume Placement Strategies, see Volume Placement Strategies.

Create a VolumePlacementStrategy custom resource

1. Create a YAML file containing the following common fields. All VolumePlacementStrategy CRDs use these fields:

   • apiVersion as portworx.io/v1beta2
   • kind as VolumePlacementStrategy
   • metadata.name with the name of your strategy

   Add any of the following affinity or antiaffinity sections to the spec:

   • replicaAffinity
   • replicaAntiAffinity
   • volumeAffinity
   • volumeAntiAffinity

   The following example adds a volumeAffinity rule to colocate Postgres volumes for performance:

   apiVersion: portworx.io/v1beta2
   kind: VolumePlacementStrategy
   metadata:
     name: postgres-volume-affinity
   spec:
     volumeAffinity:
       - matchExpressions:
         - key: app
           operator: In
           values:
             - postgres

2. Save and apply your spec with the kubectl apply command:

   kubectl apply -f yourVolumePlacementStrategy.yaml

Use the strategy in storage configurations

After you create your VolumePlacementStrategy, you can use it with your StorageClass or reference it directly in a PersistentVolumeClaim (PVC).

Use with a StorageClass

You can associate your VolumePlacementStrategy with a StorageClass and then reference that StorageClass in your PVC.

1. Create a StorageClass named storageclass_volumestrategy.yaml.
   This must include a reference to the VolumePlacementStrategy you created in the Create a VolumePlacementStrategy custom resource step above by using the placement_strategy parameter and specifying the name of your VolumePlacementStrategy:

   apiVersion: storage.k8s.io/v1
   kind: StorageClass
   metadata:
     name: postgres-storage-class
   provisioner: pxd.portworx.com
   parameters:
     placement_strategy: "postgres-volume-affinity"

2. Save and apply your StorageClass:

   kubectl apply -f storageclass_volumestrategy.yaml

3. Create a PVC that uses the storageClass:

   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
      name: postgres-pvc
   spec:
      storageClassName: postgres-storage-class
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 2Gi

4. Save and apply your PVC:

   kubectl apply -f yourPVC.yaml

Reference directly in a PVC

You can also reference your VolumePlacementStrategy directly in the PVC using an annotation.

1. Create a PVC which references the VolumePlacementStrategy you created in the Create a VolumePlacementStrategy custom resource step above by specifying placement_strategy as an annotation with the name of your VolumePlacementStrategy:

   kind: PersistentVolumeClaim
   apiVersion: v1
   metadata:
     annotations: 
       placement_strategy: "postgres-volume-affinity"
     name: postgres-pvc
   spec:
     storageClassName: postgres-storage-class
     accessModes:
       - ReadWriteOnce
     resources:
       requests:
         storage: 2Gi

2. Save and apply your PVC:

   kubectl apply -f yourPVC.yaml

After applying the VolumePlacementStrategy, StorageClass, and PVC, Portworx places the volumes according to the rules defined in the strategy. These rules are also followed during volume restores.

For information on the CRD Reference for VolumePlacementStrategies, see VolumePlacementStrategy CRD reference.

KubeVirt VMs and CSI clone

Starting with Portworx Enterprise 3.5.0, KubeVirt RWX Block VMs with only a single cloned root disk provisioned using cloneStrategy: csi-clone and no additional non-cloned data disks do not honor user-defined VPS rules at volume creation time. In this configuration, Portworx applies clone co-location behavior, placing the cloned volume replicas on the same nodes as the source volume.

To allow VPS rules to be honored, use one of the following approaches:

• Switch to copy-based cloning: Configure the StorageClass or StorageProfile to use copy-based cloning instead of CSI clone.

  Annotate the StorageClass:

  oc annotate sc <storageClassName> cdi.kubevirt.io/clone-strategy=copy --overwrite

  Or patch the StorageProfile:

  oc patch storageprofile <storage-profile-name> --type=merge -p '{"spec":{"cloneStrategy":"copy"}}'

• Add a blank data disk: Add at least one blank non-cloned data disk to the VM using the same StorageClass. With a non-cloned volume present, Portworx applies VPS rules during provisioning. Add the following entry to spec.dataVolumeTemplates in the VM spec:

  - metadata:
      name: <data-disk-name>
      annotations:
        cdi.kubevirt.io/storage.usePopulator: "false"
    spec:
      source:
        blank: {}
      storage:
        accessModes:
          - ReadWriteMany
        resources:
          requests:
            storage: <size>Gi
        storageClassName: <storageClassName>
        volumeMode: Block

For more details, see Manage Shared Block Device (RWX Block) for KubeVirt VMs.