Shared File System

A shared file system can be mounted with read/write permission from multiple pods. This may be useful for applications which can be clustered using a shared filesystem.

This example runs a shared file system for the kube-registry.

Prerequisites

This guide assumes you have created a Rook cluster as explained in the main Kubernetes guide

Multiple File Systems Not Supported

By default only one shared file system can be created with Rook. Multiple file system support in Ceph is still considered experimental and can be enabled with the environment variable ROOK_ALLOW_MULTIPLE_FILESYSTEMS defined in operator.yaml.

Please refer to cephfs experimental features page for more information.

Create the File System

Create the file system by specifying the desired settings for the metadata pool, data pools, and metadata server in the CephFilesystem CRD. In this example we create the metadata pool with replication of three and a single data pool with replication of three. For more options, see the documentation on creating shared file systems.

Save this shared file system definition as filesystem.yaml:

apiVersion: ceph.rook.io/v1
kind: CephFilesystem
metadata:
  name: myfs
  namespace: rook-ceph
spec:
  metadataPool:
    replicated:
      size: 3
  dataPools:
    - replicated:
        size: 3
  metadataServer:
    activeCount: 1
    activeStandby: true

The Rook operator will create all the pools and other resources necessary to start the service. This may take a minute to complete.

# Create the file system
$ kubectl create -f filesystem.yaml
# To confirm the file system is configured, wait for the mds pods to start
$ kubectl -n rook-ceph get pod -l app=rook-ceph-mds
NAME                                      READY     STATUS    RESTARTS   AGE
rook-ceph-mds-myfs-7d59fdfcf4-h8kw9       1/1       Running   0          12s
rook-ceph-mds-myfs-7d59fdfcf4-kgkjp       1/1       Running   0          12s

To see detailed status of the file system, start and connect to the Rook toolbox. A new line will be shown with ceph status for the mds service. In this example, there is one active instance of MDS which is up, with one MDS instance in standby-replay mode in case of failover.

$ ceph status
  ...
  services:
    mds: myfs-1/1/1 up {[myfs:0]=mzw58b=up:active}, 1 up:standby-replay

Provision Storage

Before Rook can start provisioning storage, a StorageClass needs to be created based on the filesystem. This is needed for Kubernetes to interoperate with the CSI driver to create persistent volumes.

NOTE This example uses the CSI driver, which is the preferred driver going forward for K8s 1.13 and newer. Examples are found in the CSI CephFS directory. For an example of a volume using the flex driver (required for K8s 1.12 and earlier), see the Flex Driver section below.

Save this storage class definition as storageclass.yaml:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: rook-cephfs
# Change "rook-ceph" provisioner prefix to match the operator namespace if needed
provisioner: rook-ceph.cephfs.csi.ceph.com
parameters:
  # clusterID is the namespace where operator is deployed.
  clusterID: rook-ceph
  # CephFS filesystem name into which the volume shall be created
  fsName: myfs
  # Ceph pool into which the volume shall be created
  # Required for provisionVolume: "true"
  pool: myfs-data0
  # Root path of an existing CephFS volume
  # Required for provisionVolume: "false"
  # rootPath: /absolute/path
  # The secrets contain Ceph admin credentials. These are generated automatically by the operator
  # in the same namespace as the cluster.
  csi.storage.k8s.io/provisioner-secret-name: rook-csi-cephfs-provisioner
  csi.storage.k8s.io/provisioner-secret-namespace: rook-ceph
  csi.storage.k8s.io/node-stage-secret-name: rook-csi-cephfs-node
  csi.storage.k8s.io/node-stage-secret-namespace: rook-ceph
reclaimPolicy: Delete

If you’ve deployed the Rook operator in a namespace other than “rook-ceph” as is common change the prefix in the provisioner to match the namespace you used. For example, if the Rook operator is running in “rook-op” the provisioner value should be “rook-op.rbd.csi.ceph.com”.

Create the storage class.

kubectl create -f cluster/examples/kubernetes/ceph/csi/cephfs/storageclass.yaml

Consume the Shared File System: K8s Registry Sample

As an example, we will start the kube-registry pod with the shared file system as the backing store. Save the following spec as kube-registry.yaml:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: cephfs-pvc
spec:
  accessModes:
  - ReadWriteMany
  resources:
    requests:
      storage: 1Gi
  storageClassName: csi-cephfs
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: kube-registry
  namespace: kube-system
  labels:
    k8s-app: kube-registry
    kubernetes.io/cluster-service: "true"
spec:
  replicas: 3
  selector:
    matchLabels:
      k8s-app: kube-registry
  template:
    metadata:
      labels:
        k8s-app: kube-registry
        kubernetes.io/cluster-service: "true"
    spec:
      containers:
      - name: registry
        image: registry:2
        imagePullPolicy: Always
        resources:
          limits:
            cpu: 100m
            memory: 100Mi
        env:
        # Configuration reference: https://docs.docker.com/registry/configuration/
        - name: REGISTRY_HTTP_ADDR
          value: :5000
        - name: REGISTRY_HTTP_SECRET
          value: "Ple4seCh4ngeThisN0tAVerySecretV4lue"
        - name: REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY
          value: /var/lib/registry
        volumeMounts:
        - name: image-store
          mountPath: /var/lib/registry
        ports:
        - containerPort: 5000
          name: registry
          protocol: TCP
        livenessProbe:
          httpGet:
            path: /
            port: registry
        readinessProbe:
          httpGet:
            path: /
            port: registry
      volumes:
      - name: image-store
        persistentVolumeClaim:
          claimName: cephfs-pvc
          readOnly: false

Create the Kube registry deployment:

kubectl create -f cluster/examples/kubernetes/ceph/csi/cephfs/kube-registry.yaml

You now have a docker registry which is HA with persistent storage.

Kernel Version Requirement

If the Rook cluster has more than one filesystem and the application pod is scheduled to a node with kernel version older than 4.7, inconsistent results may arise since kernels older than 4.7 do not support specifying filesystem namespaces.

Consume the Shared File System: Toolbox

Once you have pushed an image to the registry (see the instructions to expose and use the kube-registry), verify that kube-registry is using the filesystem that was configured above by mounting the shared file system in the toolbox pod. See the Direct Filesystem topic for more details.

Teardown

To clean up all the artifacts created by the file system demo:

kubectl delete -f kube-registry.yaml

To delete the filesystem components and backing data, delete the Filesystem CRD. Warning: Data will be deleted

kubectl -n rook-ceph delete cephfilesystem myfs

Flex Driver

To create a volume based on the flex driver instead of the CSI driver, see the kube-registry.yaml example manifest or refer to the complete flow in the Rook v1.0 Shared File System documentation.

Advanced Example: Erasure Coded Filesystem

The Ceph filesystem example can be found here: Ceph Shared File System - Samples - Erasure Coded.