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Chapter 5. Creating Persistent Volumes

OpenShift Container Platform clusters can be provisioned with persistent storage using GlusterFS.
Persistent volumes (PVs) and persistent volume claims (PVCs) can share volumes across a single project. While the GlusterFS-specific information contained in a PV definition could also be defined directly in a pod definition, doing so does not create the volume as a distinct cluster resource, making the volume more susceptible to conflicts.
Binding PVs by Labels and Selectors

Labels are an OpenShift Container Platform feature that support user-defined tags (key-value pairs) as part of an object’s specification. Their primary purpose is to enable the arbitrary grouping of objects by defining identical labels among them. These labels can then be targeted by selectors to match all objects with specified label values. It is this functionality we will take advantage of to enable our PVC to bind to our PV.

You can use labels to identify common attributes or characteristics shared among volumes. For example, you can define the gluster volume to have a custom attribute (key) named storage-tier with a value of gold assigned. A claim will be able to select a PV with storage-tier=gold to match this PV.
You can provision volumes either statically or dynamically. In static provisioning of volumes a persistent volume claim has to be created which the administrator uses to create a persistent volume. More details about static provisioning of volumes is provided in Section 5.1, “Static Provisioning of Volumes”.
From Container Native Storage 3.4 release onwards dynamic provisioning of volumes is introduced. With dynamic provisioning no administrator intervention is required to create a persistent volume. The volume will be created dynamically and provisioned to the application containers. More details about dynamic provisioning of volumes is provided in Section 5.2, “Dynamic Provisioning of Volumes”.

5.1. Static Provisioning of Volumes
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To enable persistent volume support in OpenShift and Kubernetes, few endpoints and a service must be created:

The sample glusterfs endpoint file (sample-gluster-endpoints.yaml) and the sample glusterfs service file (sample-gluster-service.yaml) are available at /usr/share/heketi/templates/ directory.
  1. To specify the endpoints you want to create, update the sample-gluster-endpoints.yaml file with the endpoints to be created based on the environment. Each Red Hat Gluster Storage trusted storage pool requires its own endpoint with the IP of the nodes in the trusted storage pool. 
    # cat sample-gluster-endpoints.yaml
apiVersion: v1
kind: Endpoints
metadata:
  name: glusterfs-cluster
subsets:
- addresses:
  - ip: 192.168.10.100
  ports:
  - port: 1
- addresses:
  - ip: 192.168.10.101
  ports:
  - port: 1
- addresses:
  - ip: 192.168.10.102
  ports:
  - port: 1
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    name: is the name of the endpoint
    ip: is the ip address of the Red Hat Gluster Storage nodes.
  2. Execute the following command to create the endpoints: 
    # oc create -f <name_of_endpoint_file>
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    For example: 
    # oc create -f sample-gluster-endpoints.yaml
endpoints "glusterfs-cluster" created
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  3. To verify that the endpoints are created, execute the following command: 
    # oc get endpoints
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    For example: 
    # oc get endpoints
NAME                       ENDPOINTS                                                     AGE
storage-project-router     192.168.121.233:80,192.168.121.233:443,192.168.121.233:1936   2d
glusterfs-cluster          192.168.121.168:1,192.168.121.172:1,192.168.121.233:1         3s
heketi                     10.1.1.3:8080                                                 2m
heketi-storage-endpoints   192.168.121.168:1,192.168.121.172:1,192.168.121.233:1         3m
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  4. Execute the following command to create a gluster service: 
    # oc create -f <name_of_service_file>
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    For example: 
    # oc create -f sample-gluster-service.yaml
service "glusterfs-cluster" created
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    # cat sample-gluster-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: glusterfs-cluster
spec:
  ports:
  - port: 1
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  5. To verify that the service is created, execute the following command: 
    # oc get service
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    For example: 
    # oc get service
NAME                       CLUSTER-IP      EXTERNAL-IP   PORT(S)                   AGE
storage-project-router     172.30.94.109   <none>        80/TCP,443/TCP,1936/TCP   2d
glusterfs-cluster          172.30.212.6    <none>        1/TCP                     5s
heketi                     172.30.175.7    <none>        8080/TCP                  2m
heketi-storage-endpoints   172.30.18.24    <none>        1/TCP                     3m
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    Note

    The endpoints and the services must be created for each project that requires a persistent storage.
  6. Create a 100G persistent volume with Replica 3 from GlusterFS and output a persistent volume specification describing this volume to the file pv001.json: 
    $ heketi-cli volume create --size=100 --persistent-volume-file=pv001.json
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    cat pv001.json 
{
  "kind": "PersistentVolume",
  "apiVersion": "v1",
  "metadata": {
    "name": "glusterfs-f8c612ee",
    "creationTimestamp": null
  },
  "spec": {
    "capacity": {
      "storage": "100Gi"
    },
    "glusterfs": {
      "endpoints": "TYPE ENDPOINT HERE",
      "path": "vol_f8c612eea57556197511f6b8c54b6070"
    },
    "accessModes": [
      "ReadWriteMany"
    ],
    "persistentVolumeReclaimPolicy": "Retain"
  },
  "status": {}
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    Important

    You must manually add the Labels information to the .json file.
    Following is the example YAML file for reference: 
    apiVersion: v1
kind: PersistentVolume
metadata:
 name: pv-storage-project-glusterfs1
 labels:
  storage-tier: gold
spec:
 capacity:
   storage: 12Gi
 accessModes:
   - ReadWriteMany
 persistentVolumeReclaimPolicy: Retain
 glusterfs:
   endpoints: TYPE END POINTS NAME HERE,
   path: vol_e6b77204ff54c779c042f570a71b1407
}
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    name: The name of the volume.
    storage: The amount of storage allocated to this volume
    glusterfs: The volume type being used, in this case the glusterfs plug-in
    endpoints: The endpoints name that defines the trusted storage pool created
    path: The Red Hat Gluster Storage volume that will be accessed from the Trusted Storage Pool.
    accessModes: accessModes are used as labels to match a PV and a PVC. They currently do not define any form of access control.
    lables: Use labels to identify common attributes or characteristics shared among volumes. In this case, we have defined the gluster volume to have a custom attribute (key) named storage-tier with a value of gold assigned. A claim will be able to select a PV with storage-tier=gold to match this PV.

    Note

    • heketi-cli also accepts the endpoint name on the command line (--persistent-volume-endpoint=”TYPE ENDPOINT HERE”). This can then be piped to oc create -f - to create the persistent volume immediately.
    • If there are multiple Red Hat Gluster Storage trusted storage pools in your environment, you can check on which trusted storage pool the volume is created using the heketi-cli volume list command. This command lists the cluster name. You can then update the endpoint information in the pv001.json file accordingly.
    • When creating a Heketi volume with only two nodes with the replica count set to the default value of three (replica 3), an error "No space" is displayed by Heketi as there is no space to create a replica set of three disks on three different nodes.
    • If all the heketi-cli write operations (ex: volume create, cluster create..etc) fails and the read operations ( ex: topology info, volume info ..etc) are successful, then the possibility is that the gluster volume is operating in read-only mode.
  7. Edit the pv001.json file and enter the name of the endpoint in the endpoint's section: 
    cat pv001.json
{
  "kind": "PersistentVolume",
  "apiVersion": "v1",
  "metadata": {
    "name": "glusterfs-f8c612ee",
    "creationTimestamp": null,
    "labels": {
      "storage-tier": "gold"
    }
  },
  "spec": {
    "capacity": {
      "storage": "12Gi"
    },
    "glusterfs": {
      "endpoints": "glusterfs-cluster",
      "path": "vol_f8c612eea57556197511f6b8c54b6070"
    },
    "accessModes": [
      "ReadWriteMany"
    ],
    "persistentVolumeReclaimPolicy": "Retain"
  },
  "status": {}
}
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  8. Create a persistent volume by executing the following command: 
    # oc create -f pv001.json
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    For example: 
    # oc create -f pv001.json
persistentvolume "glusterfs-4fc22ff9" created
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  9. To verify that the persistent volume is created, execute the following command: 
    # oc get pv
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    For example: 
    # oc get pv

NAME                 CAPACITY   ACCESSMODES   STATUS      CLAIM     REASON    AGE
glusterfs-4fc22ff9   100Gi      RWX           Available                       4s
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  10. Create a persistent volume claim file. For example: 
    # cat pvc.yaml
      
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: glusterfs-claim
spec:
  accessModes:
  - ReadWriteMany
  resources:
    requests:
      storage: 100Gi
    selector:
      matchLabels:
        storage-tier: gold
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  11. Bind the persistent volume to the persistent volume claim by executing the following command: 
    # oc create -f pvc.yaml
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    For example: 
    # oc create -f pvc.yaml
persistentvolumeclaim"glusterfs-claim" created
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  12. To verify that the persistent volume and the persistent volume claim is bound, execute the following commands: 
    # oc get pv
# oc get pvc
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    For example: 
    # oc get pv

NAME                 CAPACITY   ACCESSMODES   STATUS    CLAIM                  REASON    AGE
glusterfs-4fc22ff9   100Gi      RWX           Bound     storage-project/glusterfs-claim             1m
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    # oc get pvc

NAME              STATUS    VOLUME               CAPACITY   ACCESSMODES   AGE
glusterfs-claim   Bound     glusterfs-4fc22ff9   100Gi      RWX           11s
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  13. The claim can now be used in the application:
    For example: 
    # cat app.yaml

apiVersion: v1
kind: Pod
metadata:
  name: busybox
spec:
  containers:
    - image: busybox
      command:
        - sleep
        - "3600"
      name: busybox
      volumeMounts:
        - mountPath: /usr/share/busybox
          name: mypvc
  volumes:
    - name: mypvc
      persistentVolumeClaim:
        claimName: glusterfs-claim
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    # oc create -f app.yaml
pod "busybox" created
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    For more information about using the glusterfs claim in the application see, https://access.redhat.com/documentation/en/openshift-container-platform/3.5/single/installation-and-configuration/#install-config-storage-examples-gluster-example.
  14. To verify that the pod is created, execute the following command: 
    # oc get pods
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  15. To verify that the persistent volume is mounted inside the container, execute the following command: 
    # oc rsh busybox
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    / $ df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/mapper/docker-253:0-1310998-81732b5fd87c197f627a24bcd2777f12eec4ee937cc2660656908b2fa6359129
                      100.0G     34.1M     99.9G   0% /
tmpfs                     1.5G         0      1.5G   0% /dev
tmpfs                     1.5G         0      1.5G   0% /sys/fs/cgroup
192.168.121.168:vol_4fc22ff934e531dec3830cfbcad1eeae
                       99.9G     66.1M     99.9G   0% /usr/share/busybox
tmpfs                     1.5G         0      1.5G   0% /run/secrets
/dev/mapper/vg_vagrant-lv_root
                       37.7G      3.8G     32.0G  11% /dev/termination-log
tmpfs                     1.5G     12.0K      1.5G   0% /var/run/secretgit s/kubernetes.io/serviceaccount
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Note

If you encounter a permission denied error on the mount point, then refer to section Gluster Volume Security at: https://access.redhat.com/documentation/en/openshift-container-platform/3.5/single/installation-and-configuration/#gluster-volume-security.
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