OpenEBS Local PV Hostpath User Guide

This guide will help you to set up and use OpenEBS Local Persistent Volumes backed by Hostpath.

OpenEBS Dynamic Local PV provisioner can create Kubernetes Local Persistent Volumes using a unique Hostpath (directory) on the node to persist data, hereafter referred to as OpenEBS Local PV Hostpath volumes.

OpenEBS Local PV Hostpath volumes have the following advantages compared to native Kubernetes hostpath volumes.

  • OpenEBS Local PV Hostpath allows your applications to access hostpath via StorageClass, PVC, and PV. This provides you the flexibility to change the PV providers without having to redesign your Application YAML.
  • Data protection using the Velero Backup and Restore.
  • Protect against hostpath security vulnerabilities by masking the hostpath completely from the application YAML and pod.

OpenEBS Local PV uses volume topology aware pod scheduling enhancements introduced by Kubernetes Local Volumes

Local PV Hostpath - 图1

QUICKSTART

OpenEBS Local PV Hostpath volumes will be created under /var/openebs/local directory. You can customize the location by configuring install parameters or by creating new StorageClass.

If you have OpenEBS already installed, you can create an example pod that persists data to OpenEBS Local PV Hostpath with following kubectl commands.

  1. kubectl apply -f https://openebs.github.io/charts/examples/local-hostpath/local-hostpath-pvc.yaml
  2. kubectl apply -f https://openebs.github.io/charts/examples/local-hostpath/local-hostpath-pod.yaml

Verify using below kubectl commands that example pod is running and is using a OpenEBS Local PV Hostpath.

  1. kubectl get pod hello-local-hostpath-pod
  2. kubectl get pvc local-hostpath-pvc

For a more detailed walkthrough of the setup, follow along the rest of this document.

Minimum Versions

  • Kubernetes 1.12 or higher is required
  • OpenEBS 1.0 or higher is required.

Prerequisites

Setup the directory on the nodes where Local PV Hostpaths will be created. This directory will be referred to as BasePath. The default location is /var/openebs/local.

BasePath can be any of the following:

  • A directory on root disk (or os disk). (Example: /var/openebs/local).
  • In the case of bare-metal Kubernetes nodes, a mounted directory using the additional drive or SSD. (Example: An SSD available at /dev/sdb, can be formatted with Ext4 and mounted as /mnt/openebs-local)
  • In the case of cloud or virtual instances, a mounted directory created from attaching an external cloud volume or virtual disk. (Example, in GKE, a Local SSD can be used which will be available at /mnt/disk/ssd1.)

Local PV Hostpath - 图2

air-gapped environment

If you are running your Kubernetes cluster in an air-gapped environment, make sure the following container images are available in your local repository.

  • quay.io/openebs/localpv-provisioner
  • quay.io/openebs/linux-utils

Local PV Hostpath - 图3

Rancher RKE cluster

If you are using the Rancher RKE cluster, you must configure kubelet service with extra_binds for BasePath. If your BasePath is the default directory /var/openebs/local, then extra_binds section should have the following details:

  1. services:
  2.   kubelet:
  3.     extra_binds:
  4.       - /var/openebs/local:/var/openebs/local

Install

You can skip this section if you have already installed OpenEBS.

  1. Prepare to install OpenEBS by providing custom values for configurable parameters.

    OpenEBS Dynamic Local Provisioner offers some configurable parameters that can be applied during the OpenEBS Installation. Some key configurable parameters available for OpenEBS Dynamic Local Provisioner are:

    • The location of the OpenEBS Dynamic Local PV provisioner container image.

      Default value: quay.io/openebs/provisioner-localpv YAML specification: spec.image on Deployment(localpv-provisioner) Helm key: localprovisioner.image

    • The location of the Provisioner Helper container image. OpenEBS Dynamic Local Provisioner create a Provisioner Helper pod to create and delete hostpath directories on the nodes.

      Default value: quay.io/openebs/linux-utils YAML specification: Environment Variable (OPENEBS_IO_HELPER_IMAGE) on Deployment(localpv-provisioner) Helm key: helper.image

    • The absolute path on the node where the Hostpath directory of a Local PV Volume will be created.

      Default value: /var/openebs/local YAML specification: Environment Variable (OPENEBS_IO_LOCALPV_HOSTPATH_DIR) on Deployment(maya-apiserver) Helm key: localprovisioner.basePath

  2. You can proceed to install OpenEBS either using kubectl or helm using the steps below.

    • Install using kubectl

      If you would like to change the default values for any of the configurable parameters mentioned in the previous step, download the openebs-operator.yaml and make the necessary changes before applying.

      1. kubectl apply -f https://openebs.github.io/charts/openebs-operator.yaml

    • Install using helm stable charts

      If you would like to change the default values for any of the configurable parameters mentioned in the previous step, specify each parameter using the --set key=value[,key=value] argument to helm install.

      1. helm repo update
      2. helm install --namespace openebs --name openebs stable/openebs

Create StorageClass

You can skip this section if you would like to use default OpenEBS Local PV Hostpath StorageClass created by OpenEBS.

The default Storage Class is called openebs-hostpath and its BasePath is configured as /var/openebs/local.

  1. To create your own StorageClass with custom BasePath, save the following StorageClass definition as local-hostpath-sc.yaml

    1. apiVersion: storage.k8s.io/v1
    2. kind: StorageClass
    3. metadata:
    4.   name: local-hostpath
    5.   annotations:
    6.     openebs.io/cas-type: local
    7.     cas.openebs.io/config: |
    8.       - name: StorageType
    9.         value: hostpath
    10.       - name: BasePath
    11.         value: /var/local-hostpath
    12. provisioner: openebs.io/local
    13. reclaimPolicy: Delete
    14. volumeBindingMode: WaitForFirstConsumer

    Local PV Hostpath - 图4

    note

    The volumeBindingMode MUST ALWAYS be set to WaitForFirstConsumer. volumeBindingMode: WaitForFirstConsumer instructs Kubernetes to initiate the creation of PV only after Pod using PVC is scheduled to the node.

  2. Edit local-hostpath-sc.yaml and update with your desired values for metadata.name and cas.openebs.io/config.BasePath.

    Local PV Hostpath - 图5

    note

    If the BasePath does not exist on the node, OpenEBS Dynamic Local PV Provisioner will attempt to create the directory, when the first Local Volume is scheduled on to that node. You MUST ensure that the value provided for BasePath is a valid absolute path.

  3. Create OpenEBS Local PV Hostpath Storage Class.

    1. kubectl apply -f local-hostpath-sc.yaml

  4. Verify that the StorageClass is successfully created.

    1. kubectl get sc local-hostpath -o yaml

Install verification

Once you have installed OpenEBS, verify that OpenEBS Local PV provisioner is running and Hostpath StorageClass is created.

  1. To verify OpenEBS Local PV provisioner is running, execute the following command. Replace -n openebs with the namespace where you installed OpenEBS.

    1. kubectl get pods -n openebs -l openebs.io/component-name=openebs-localpv-provisioner

    The output should indicate openebs-localpv-provisioner pod is running.

    NAME READY STATUS RESTARTS AGE openebs-localpv-provisioner-5ff697f967-nb7f4 1/1 Running 0 2m49s

  2. To verify OpenEBS Local PV Hostpath Storageclass is created, execute the following command.

    1. kubectl get sc

    The output should indicate either the default StorageClass openebs-hostpath and/or custom StorageClass local-hostpath are displayed.

    NAME PROVISIONER AGE local-hostpath openebs.io/local 5h26m openebs-hostpath openebs.io/local 6h4m

Create a PersistentVolumeClaim

The next step is to create a PersistentVolumeClaim. Pods will use PersistentVolumeClaims to request Hostpath Local PV from OpenEBS Dynamic Local PV provisioner.

  1. Here is the configuration file for the PersistentVolumeClaim. Save the following PersistentVolumeClaim definition as local-hostpath-pvc.yaml

    1. kind: PersistentVolumeClaim
    2. apiVersion: v1
    3. metadata:
    4.   name: local-hostpath-pvc
    5. spec:
    6.   storageClassName: openebs-hostpath
    7.   accessModes:
    8.     - ReadWriteOnce
    9.   resources:
    10.     requests:
    11.       storage: 5G

  2. Create the PersistentVolumeClaim

    1. kubectl apply -f local-hostpath-pvc.yaml

  3. Look at the PersistentVolumeClaim:

    1. kubectl get pvc local-hostpath-pvc

    The output shows that the STATUS is Pending. This means PVC has not yet been used by an application pod. The next step is to create a Pod that uses your PersistentVolumeClaim as a volume.

    NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE local-hostpath-pvc Pending openebs-hostpath 3m7s

Create Pod to consume OpenEBS Local PV Hospath Storage

  1. Here is the configuration file for the Pod that uses Local PV. Save the following Pod definition to local-hostpath-pod.yaml.

    1. apiVersion: v1
    2. kind: Pod
    3. metadata:
    4.   name: hello-local-hostpath-pod
    5. spec:
    6.   volumes:
    7.   - name: local-storage
    8.     persistentVolumeClaim:
    9.       claimName: local-hostpath-pvc
    10.   containers:
    11.   - name: hello-container
    12.     image: busybox
    13.     command:
    14.        - sh
    15.        - -c
    16.        - 'while true; do echo "`date` [`hostname`] Hello from OpenEBS Local PV." >> /mnt/store/greet.txt; sleep $(($RANDOM % 5 + 300)); done'
    17.     volumeMounts:
    18.     - mountPath: /mnt/store
    19.       name: local-storage

    Local PV Hostpath - 图6

    note

    As the Local PV storage classes use waitForFirstConsumer, do not use nodeName in the Pod spec to specify node affinity. If nodeName is used in the Pod spec, then PVC will remain in pending state. For more details refer https://github.com/openebs/openebs/issues/2915.

  2. Create the Pod:

    1. kubectl apply -f local-hostpath-pod.yaml

  3. Verify that the container in the Pod is running.

    1. kubectl get pod hello-local-hostpath-pod

  4. Verify that the data is being written to the volume.

    1. kubectl exec hello-local-hostpath-pod -- cat /mnt/store/greet.txt

  5. Verify that the container is using the Local PV Hostpath.

    1. kubectl describe pod hello-local-hostpath-pod

    The output shows that the Pod is running on Node: gke-kmova-helm-default-pool-3a63aff5-1tmf and using the peristent volume provided by local-hostpath-pvc.

    Name: hello-local-hostpath-pod Namespace: default Priority: 0 Node: gke-kmova-helm-default-pool-3a63aff5-1tmf/10.128.0.28 Start Time: Thu, 16 Apr 2020 17:56:04 +0000 … Volumes: local-storage: Type: PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace) ClaimName: local-hostpath-pvc ReadOnly: false …

  6. Look at the PersistentVolumeClaim again to see the details about the dynamically provisioned Local PersistentVolume

    1. kubectl get pvc local-hostpath-pvc

    The output shows that the STATUS is Bound. A new Persistent Volume pvc-864a5ac8-dd3f-416b-9f4b-ffd7d285b425 has been created.

    NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE local-hostpath-pvc Bound pvc-864a5ac8-dd3f-416b-9f4b-ffd7d285b425 5G RWO openebs-hostpath 28m

  7. Look at the PersistentVolume details to see where the data is stored. Replace the PVC name with the one that was displayed in the previous step.

    1. kubectl get pv pvc-864a5ac8-dd3f-416b-9f4b-ffd7d285b425 -o yaml

    The output shows that the PV was provisioned in response to PVC request spec.claimRef.name: local-hostpath-pvc.

    apiVersion: v1 kind: PersistentVolume metadata: name: pvc-864a5ac8-dd3f-416b-9f4b-ffd7d285b425 annotations: pv.kubernetes.io/provisioned-by: openebs.io/local … spec: accessModes: - ReadWriteOnce capacity: storage: 5G claimRef: apiVersion: v1 kind: PersistentVolumeClaim name: local-hostpath-pvc namespace: default resourceVersion: “291148” uid: 864a5ac8-dd3f-416b-9f4b-ffd7d285b425 … … local: fsType: “” path: /var/openebs/local/pvc-864a5ac8-dd3f-416b-9f4b-ffd7d285b425 nodeAffinity: required: nodeSelectorTerms: - matchExpressions: - key: kubernetes.io/hostname operator: In values: - gke-kmova-helm-default-pool-3a63aff5-1tmf persistentVolumeReclaimPolicy: Delete storageClassName: openebs-hostpath volumeMode: Filesystem status: phase: Bound

Local PV Hostpath - 图7

note

A few important characteristics of a OpenEBS Local PV can be seen from the above output:

  • spec.nodeAffinity specifies the Kubernetes node where the Pod using the Hostpath volume is scheduled.
  • spec.local.path specifies the unique subdirectory under the BasePath (/var/local/openebs) defined in corresponding StorageClass.

Cleanup

Delete the Pod, the PersistentVolumeClaim and StorageClass that you might have created.

  1. kubectl delete pod hello-local-hostpath-pod
  2. kubectl delete pvc local-hostpath-pvc
  3. kubectl delete sc local-hostpath

Verify that the PV that was dynamically created is also deleted.

  1. kubectl get pv

Backup and Restore

OpenEBS Local Volumes can be backed up and restored along with the application using Velero.

Local PV Hostpath - 图8

note

The following steps assume that you already have Velero with Restic integration is configured. If not, please follow the Velero Documentation to proceed with install and setup of Velero. If you encounter any issues or have questions, talk to us on the #openebs channel on the Kubernetes Slack server.

Backup

The following steps will help you to prepare and backup the data from the volume created for the example pod (hello-local-hostpath-pod), with the volume mount (local-storage).

  1. Prepare the application pod for backup. Velero uses Kubernetes labels to select the pods that need to be backed up. Velero uses annotation on the pods to determine which volumes need to be backed up. For the example pod launched in this guide, you can inform velero to backup by specifing the following label and annotation.

    1. kubectl label pod hello-local-hostpath-pod app=test-velero-backup
    2. kubectl annotate pod hello-local-hostpath-pod backup.velero.io/backup-volumes=local-storage

  2. Create a Backup using velero.

    1. velero backup create bbb-01 -l app=test-velero-backup

  3. Verify that backup is successful.

    1. velero backup describe bbb-01 --details

    On successful completion of the backup, the output of the backup describe command will show the following:

    … Restic Backups: Completed: default/hello-local-hostpath-pod: local-storage

Restore

  1. Install and Setup Velero, with the same provider where backups were saved. Verify that backups are accessible.

    1. velero backup get

    The output of should display the backups that were taken successfully.

    NAME STATUS CREATED EXPIRES STORAGE LOCATION SELECTOR bbb-01 Completed 2020-04-25 15:49:46 +0000 UTC 29d default app=test-velero-backup

  2. Restore the application.

    Local PV Hostpath - 图9

    note

    Local PVs are created with node affinity. As the node names will change when a new cluster is created, create the required PVC(s) prior to proceeding with restore.

    Replace the path to the PVC yaml in the below commands, with the PVC that you have created.

    1. kubectl apply -f https://openebs.github.io/charts/examples/local-hostpath/local-hostpath-pvc.yaml
    2. velero restore create rbb-01 --from-backup bbb-01 -l app=test-velero-backup

  3. Verify that application is restored.

    1. velero restore describe rbb-01

    Depending on the data, it may take a while to initialize the volume. On successful restore, the output of the above command should show:

    … Restic Restores (specify —details for more information): Completed: 1

  4. Verify that data has been restored. The application pod used in this example, write periodic messages (greetings) to the volume.

    1. kubectl exec hello-local-hostpath-pod -- cat /mnt/store/greet.txt

    The output will show that backed up data as well as new greetings that started appearing after application pod was restored.

    Sat Apr 25 15:41:30 UTC 2020 [hello-local-hostpath-pod] Hello from OpenEBS Local PV. Sat Apr 25 15:46:30 UTC 2020 [hello-local-hostpath-pod] Hello from OpenEBS Local PV. Sat Apr 25 16:11:25 UTC 2020 [hello-local-hostpath-pod] Hello from OpenEBS Local PV.

Troubleshooting

Review the logs of the OpenEBS Local PV provisioner. OpenEBS Dynamic Local Provisioner logs can be fetched using.

  1. kubectl logs -n openebs -l openebs.io/component-name=openebs-localpv-provisioner

Support

If you encounter issues or have a question, file an Github issue, or talk to us on the #openebs channel on the Kubernetes Slack server.

See Also:

Understand OpenEBS Local PVs

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