Complete Example Using GlusterFS - Persistent Storage Examples | Configuring Clusters

Overview
Prerequisites
Static Provisioning
Using the Storage

Overview

This topic provides an end-to-end example of how to use an existing converged mode, independent mode, or standalone Red Hat Gluster Storage cluster as persistent storage for OpenShift Container Platform. It is assumed that a working Red Hat Gluster Storage cluster is already set up. For help installing converged mode or independent mode, see Persistent Storage Using Red Hat Gluster Storage. For standalone Red Hat Gluster Storage, consult the Red Hat Gluster Storage Administration Guide.

For an end-to-end example of how to dynamically provision GlusterFS volumes, see Complete Example Using GlusterFS for Dynamic Provisioning.

All oc commands are executed on the OpenShift Container Platform master host.

Prerequisites

To access GlusterFS volumes, the mount.glusterfs command must be available on all schedulable nodes. For RPM-based systems, the glusterfs-fuse package must be installed:

# yum install glusterfs-fuse

This package comes installed on every RHEL system. However, it is recommended to update to the latest available version from Red Hat Gluster Storage if your servers use x86_64 architecture. To do this, the following RPM repository must be enabled:

# subscription-manager repos --enable=rh-gluster-3-client-for-rhel-7-server-rpms

If glusterfs-fuse is already installed on the nodes, ensure that the latest version is installed:

# yum update glusterfs-fuse

By default, SELinux does not allow writing from a pod to a remote Red Hat Gluster Storage server. To enable writing to Red Hat Gluster Storage volumes with SELinux on, run the following on each node running GlusterFS:

$ sudo setsebool -P virt_sandbox_use_fusefs on (1)
$ sudo setsebool -P virt_use_fusefs on

1	The `-P` option makes the boolean persistent between reboots.

The virt_sandbox_use_fusefs boolean is defined by the docker-selinux package. If you get an error saying it is not defined, ensure that this package is installed.

If you use Atomic Host, the SELinux booleans are cleared when you upgrade Atomic Host. When you upgrade Atomic Host, you must set these boolean values again.

Static Provisioning

To enable static provisioning, first create a GlusterFS volume. See the Red Hat Gluster Storage Administration Guide for information on how to do this using the gluster command-line interface or the heketi project site for information on how to do this using heketi-cli. For this example, the volume will be named myVol1.

Define the following Service and Endpoints in gluster-endpoints.yaml:

---
apiVersion: v1
kind: Service
metadata:
  name: glusterfs-cluster (1)
spec:
  ports:
  - port: 1
---
apiVersion: v1
kind: Endpoints
metadata:
  name: glusterfs-cluster (1)
subsets:
  - addresses:
      - ip: 192.168.122.221 (2)
    ports:
      - port: 1 (3)
  - addresses:
      - ip: 192.168.122.222 (2)
    ports:
      - port: 1 (3)
  - addresses:
      - ip: 192.168.122.223 (2)
    ports:
      - port: 1 (3)

1	These names must match.
2	The `ip` values must be the actual IP addresses of a Red Hat Gluster Storage server, not hostnames.
3	The port number is ignored.

From the OpenShift Container Platform master host, create the Service and Endpoints:

$ oc create -f gluster-endpoints.yaml
service "glusterfs-cluster" created
endpoints "glusterfs-cluster" created

Verify that the Service and Endpoints were created:

$ oc get services
NAME                       CLUSTER_IP       EXTERNAL_IP   PORT(S)    SELECTOR        AGE
glusterfs-cluster          172.30.205.34    <none>        1/TCP      <none>          44s

$ oc get endpoints
NAME                ENDPOINTS                                               AGE
docker-registry     10.1.0.3:5000                                           4h
glusterfs-cluster   192.168.122.221:1,192.168.122.222:1,192.168.122.223:1   11s
kubernetes          172.16.35.3:8443                                        4d

Endpoints are unique per project. Each project accessing the GlusterFS volume needs its own Endpoints.

In order to access the volume, the container must run with either a user ID (UID) or group ID (GID) that has access to the file system on the volume. This information can be discovered in the following manner:
```
$ mkdir -p /mnt/glusterfs/myVol1

$ mount -t glusterfs 192.168.122.221:/myVol1 /mnt/glusterfs/myVol1

$ ls -lnZ /mnt/glusterfs/
drwxrwx---. 592 590 system_u:object_r:fusefs_t:s0    myVol1  (1) (2)
```
1 The UID is 592.

2 The GID is 590.

Define the following PersistentVolume (PV) in gluster-pv.yaml:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: gluster-default-volume (1)
  annotations:
    pv.beta.kubernetes.io/gid: "590" (2)
spec:
  capacity:
    storage: 2Gi (3)
  accessModes: (4)
    - ReadWriteMany
  glusterfs:
    endpoints: glusterfs-cluster (5)
    path: myVol1 (6)
    readOnly: false
  persistentVolumeReclaimPolicy: Retain

1	The name of the volume.
2	The GID on the root of the GlusterFS volume.
3	The amount of storage allocated to this volume.
4	`accessModes` are used as labels to match a PV and a PVC. They currently do not define any form of access control.
5	The Endpoints resource previously created.
6	The GlusterFS volume that will be accessed.

From the OpenShift Container Platform master host, create the PV:
```
$ oc create -f gluster-pv.yaml
```

Verify that the PV was created:

$ oc get pv
NAME                     LABELS    CAPACITY     ACCESSMODES   STATUS      CLAIM     REASON    AGE
gluster-default-volume   <none>    2147483648   RWX           Available                       2s

Create a PersistentVolumeClaim (PVC) that will bind to the new PV in gluster-claim.yaml:
```
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: gluster-claim  (1)
spec:
  accessModes:
  - ReadWriteMany      (2)
  resources:
     requests:
       storage: 1Gi    (3)
```
1 The claim name is referenced by the pod under its volumes section.

2 Must match the accessModes of the PV.

3 This claim will look for PVs offering 1Gi or greater capacity.
From the OpenShift Container Platform master host, create the PVC:
```
$ oc create -f gluster-claim.yaml
```

Verify that the PV and PVC are bound:

$ oc get pv
NAME         LABELS    CAPACITY   ACCESSMODES   STATUS      CLAIM          REASON    AGE
gluster-pv   <none>    1Gi        RWX           Available   gluster-claim            37s

$ oc get pvc
NAME            LABELS    STATUS    VOLUME       CAPACITY   ACCESSMODES   AGE
gluster-claim   <none>    Bound     gluster-pv   1Gi        RWX           24s

PVCs are unique per project. Each project accessing the GlusterFS volume needs its own PVC. PVs are not bound to a single project, so PVCs across multiple projects may refer to the same PV.

Using the Storage

At this point, you have a dynamically created GlusterFS volume bound to a PVC. You can now utilize this PVC in a pod.

Create the pod object definition:

apiVersion: v1
kind: Pod
metadata:
  name: hello-openshift-pod
  labels:
    name: hello-openshift-pod
spec:
  containers:
  - name: hello-openshift-pod
    image: openshift/hello-openshift
    ports:
    - name: web
      containerPort: 80
    volumeMounts:
    - name: gluster-vol1
      mountPath: /usr/share/nginx/html
      readOnly: false
  volumes:
  - name: gluster-vol1
    persistentVolumeClaim:
      claimName: gluster1 (1)

1	The name of the PVC created in the previous step.

From the OpenShift Container Platform master host, create the pod:

# oc create -f hello-openshift-pod.yaml
pod "hello-openshift-pod" created

View the pod. Give it a few minutes, as it might need to download the image if it does not already exist:

# oc get pods -o wide
NAME                               READY     STATUS    RESTARTS   AGE       IP               NODE
hello-openshift-pod                          1/1       Running   0          9m        10.38.0.0        node1

oc exec into the container and create an index.html file in the mountPath definition of the pod:

$ oc exec -ti hello-openshift-pod /bin/sh
$ cd /usr/share/nginx/html
$ echo 'Hello OpenShift!!!' > index.html
$ ls
index.html
$ exit

Now curl the URL of the pod:

# curl http://10.38.0.0
Hello OpenShift!!!

Delete the pod, recreate it, and wait for it to come up:

# oc delete pod hello-openshift-pod
pod "hello-openshift-pod" deleted
# oc create -f hello-openshift-pod.yaml
pod "hello-openshift-pod" created
# oc get pods -o wide
NAME                               READY     STATUS    RESTARTS   AGE       IP               NODE
hello-openshift-pod                          1/1       Running   0          9m        10.37.0.0        node1

Now curl the pod again and it should still have the same data as before. Note that its IP address may have changed:
```
# curl http://10.37.0.0
Hello OpenShift!!!
```

Check that the index.html file was written to GlusterFS storage by doing the following on any of the nodes:

$ mount | grep heketi
/dev/mapper/VolGroup00-LogVol00 on /var/lib/heketi type xfs (rw,relatime,seclabel,attr2,inode64,noquota)
/dev/mapper/vg_f92e09091f6b20ab12b02a2513e4ed90-brick_1e730a5462c352835055018e1874e578 on /var/lib/heketi/mounts/vg_f92e09091f6b20ab12b02a2513e4ed90/brick_1e730a5462c352835055018e1874e578 type xfs (rw,noatime,seclabel,nouuid,attr2,inode64,logbsize=256k,sunit=512,swidth=512,noquota)
/dev/mapper/vg_f92e09091f6b20ab12b02a2513e4ed90-brick_d8c06e606ff4cc29ccb9d018c73ee292 on /var/lib/heketi/mounts/vg_f92e09091f6b20ab12b02a2513e4ed90/brick_d8c06e606ff4cc29ccb9d018c73ee292 type xfs (rw,noatime,seclabel,nouuid,attr2,inode64,logbsize=256k,sunit=512,swidth=512,noquota)

$ cd /var/lib/heketi/mounts/vg_f92e09091f6b20ab12b02a2513e4ed90/brick_d8c06e606ff4cc29ccb9d018c73ee292/brick
$ ls
index.html
$ cat index.html
Hello OpenShift!!!

1	The claim name is referenced by the pod under its `volumes` section.
2	Must match the `accessModes` of the PV.
3	This claim will look for PVs offering 1Gi or greater capacity.

1	The UID is 592.
2	The GID is 590.