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Version: 3.2

Automatically expand Portworx storage pools in Tanzu

Summary and Key concepts

Summary:​

This article explains how to use Portworx Autopilot to automatically expand storage pools when they begin running out of space. Autopilot monitors storage pool metrics (e.g., via Prometheus) and triggers resizing actions when high usage conditions are detected. The example provided demonstrates how to create an Autopilot rule that resizes a storage pool by 50% when its available capacity drops below 50%, up to a maximum of 400GiB. The article includes YAML specs for creating a PostgreSQL application with persistent volumes, configuring storage pools, and applying the Autopilot rule. It also provides monitoring instructions for tracking the rule's execution using Kubernetes events.

Kubernetes Concepts:​

  • PersistentVolumeClaim (PVC): A request for storage in Kubernetes. The example includes a PostgreSQL application with PVCs to demonstrate Autopilot's pool expansion feature.
  • StorageClass: Specifies how storage is provisioned in Kubernetes. The article includes a Portworx storage class definition for PVC expansion.

Portworx Concepts:​

  • Autopilot: A feature that automates the expansion of storage pools and PVCs based on predefined rules and metrics.
  • Storage Pool: A Portworx construct representing a collection of storage resources, which Autopilot can scale or rebalance.

You can use Autopilot to expand Portworx storage pools automatically when they begin to run out of space. Autopilot monitors the metrics in your cluster (e.g., via Prometheus) and detects high usage conditions. Once high usage conditions occur, Autopilot communicates with Portworx to resize the pool.

Autopilot uses Portworx APIs to expand storage pools, and these APIs support the VMware vSphere cloud provider.

Prerequisites​

  • Portworx cloud drives: Your Portworx installation must use one of the supported cloud drives where Portworx provisions the backing drives using the cloud provider
  • Autopilot version: 1.2.13 and above

Example spec​

You can use the auto scale type to automatically expand the Portworx storage pool. You can also specify the add-drive or resize-drive scale type based on your specific use case.

The following example Autopilot rules use the different scale types supported to resize all Portworx storage pools in the cluster until each pool exceeds 400 GiB. For more information about scale types, refer to openstorage.io.action.storagepool/expand.

apiVersion: autopilot.libopenstorage.org/v1alpha1
kind: AutopilotRule
metadata:
  name: pool-expand
spec:
  enforcement: required
  ##### conditions are the symptoms to evaluate. All conditions are AND'ed.
  conditions:
    expressions:
    # Pool available capacity is less than 50%
    - key: "100 * (px_pool_stats_available_bytes / px_pool_stats_total_bytes)"
      operator: Lt
      values:
        - "50"
    # Total pool capacity should not exceed 400 GiB
    - key: "px_pool_stats_total_bytes / (1024 * 1024 * 1024)"
      operator: Lt
      values:
        - "400"
  ##### action to perform when conditions are true
  actions:
    - name: "openstorage.io.action.storagepool/expand"
      params:
        # Auto-scale the pool by a percentage of its current size
        scalepercentage: "50"
        # When scaling, use auto-scaling logic
        scaletype: "auto"

Key Sections in the Spec

  • The conditions section establishes threshold criteria dictating when the rule must perform its action. In this example, that criteria contains two formulas:

    • 100 * (px_pool_stats_available_bytes / px_pool_stats_total_bytes):
      • This calculates the percentage of available capacity in the pool.
      • The Lt (less than) operator sets a condition that the pool’s available capacity percentage must be less than 50%.
    • px_pool_stats_total_bytes / (1024 * 1024 * 1024):
      • This calculates the total pool capacity in GiB.
      • The Lt operator limits the pool size to a maximum of 400 GiB.

    These conditions are combined using logical operator AND, meaning all conditions must be true for the rule to trigger.

  • The actions section specifies the operation that Portworx performs when the conditions are met. Action parameters control the behavior of the action, and different actions include different parameters. In this example, the actions section directs Portworx to:

    • Increase the pool size by 50% of its current size (scalepercentage: "50").
    • The auto scale type is used, allowing Autopilot to either add new drives or resize existing ones automatically, based on available resources and configuration.

note

When you expand your storage pool using the add-drive scale type, Autopilot increases your pool storage capacity by adding new drives to the pool based on the scale percentage. The new drives will match the capacity of the existing ones because the storage pool consists of drives of equal size. For example, if your current pool consists of 100 GiB drive, with add-drive scale type, a 100 GiB drive is added to your pool, thus expanding it by 100%. In such cases, scale percentage represents the minimum percentage by which Portworx will scale up the pool.

Define and add Autopilot rule​

Perform the following steps to deploy the above example.

Create application and PVC specs​

note

The specs below create an application that writes 300 GiB of data to a 400 GiB volume. If your Storage pools are larger than that, you must change these numbers to ensure the capacity condition triggers.

First, create the storage and application spec files:

  1. Create postgres-sc.yaml and place the following content inside it.

    ##### Portworx storage class
    apiVersion: storage.k8s.io/v1
    kind: StorageClass
    metadata:
      name: postgres-pgbench-sc
    provisioner: pxd.portworx.com
    parameters:
      repl: "2"
    allowVolumeExpansion: true

  2. Create postgres-vol.yaml and place the following content inside it.

    kind: PersistentVolumeClaim
    apiVersion: v1
    metadata:
      name: pgbench-data
    spec:
      storageClassName: postgres-pgbench-sc
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 400Gi
    ---
    kind: PersistentVolumeClaim
    apiVersion: v1
    metadata:
      name: pgbench-state
    spec:
      storageClassName: postgres-pgbench-sc
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 1Gi

  3. Create postgres-app.yaml and place the following content inside it.

    The application in this example is a PostgreSQL database with a pgbench sidecar. The SIZE environment variable in this spec instructs pgbench to write 300GiB of data to the volume. Since the volume is 400GiB in size, Autopilot will resize the storage pool when the conditions threshold is crossed.

    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: pgbench
      labels:
        app: pgbench
    spec:
      selector:
        matchLabels:
          app: pgbench
      strategy:
        rollingUpdate:
          maxSurge: 1
          maxUnavailable: 1
        type: RollingUpdate
      replicas: 1
      template:
        metadata:
          labels:
            app: pgbench
        spec:
          schedulerName: stork
          containers:
            - image: postgres:9.5
              name: postgres
              ports:
              - containerPort: 5432
              env:
              - name: POSTGRES_USER
                value: pgbench
              - name: POSTGRES_PASSWORD
                value: superpostgres
              - name: PGBENCH_PASSWORD
                value: superpostgres
              - name: PGDATA
                value: /var/lib/postgresql/data/pgdata
              volumeMounts:
              - mountPath: /var/lib/postgresql/data
                name: pgbenchdb
            - name: pgbench
              image: portworx/torpedo-pgbench:latest
              imagePullPolicy: "Always"
              env:
                - name: PG_HOST
                  value: 127.0.0.1
                - name: PG_USER
                  value: pgbench
                - name: SIZE
                  value: "300"
              volumeMounts:
              - mountPath: /var/lib/postgresql/data
                name: pgbenchdb
              - mountPath: /pgbench
                name: pgbenchstate
          volumes:
          - name: pgbenchdb
            persistentVolumeClaim:
              claimName: pgbench-data
          - name: pgbenchstate
            persistentVolumeClaim:
              claimName: pgbench-state

AutopilotRule spec​

Once you've created your storage and application specs, you can create an AutopilotRule that controls them.

Use the example spec and create a YAML spec for the autopilot rule named autopilotrule-pool-expand-example.yaml.

Apply specs​

Once you've designed your specs, deploy them.

kubectl apply -f autopilotrule-pool-expand-example.yaml
kubectl apply -f postgres-sc.yaml
kubectl apply -f postgres-vol.yaml
kubectl apply -f postgres-app.yaml

Monitor​

Observe how the pgbench pod starts filling up the pgbench-data PVCs and, by extension, the underlying Portworx storage pools. As the pool usage exceeds 50%, Autopilot resizes the storage pools.

You can enter the following command to retrieve all the events generated for the pool-expand rule:

kubectl get events --field-selector involvedObject.kind=AutopilotRule,involvedObject.name=pool-expand --all-namespaces --sort-by .lastTimestamp

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