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Filesystem Storage Overview

A filesystem storage (also named shared filesystem) 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 filesystem for the kube-registry.

Prerequisites

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

Create the Filesystem

Create the filesystem 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 filesystems.

Save this shared filesystem definition as filesystem.yaml:

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

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# Create the filesystem
kubectl create -f filesystem.yaml
[...]

To confirm the filesystem is configured, wait for the mds pods to start:

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$ 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 filesystem, 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.

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$ 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.

Save this storage class definition as storageclass.yaml:

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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 the rook cluster is running
  # If you change this namespace, also change the namespace below where the secret namespaces are defined
  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-replicated

  # 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/controller-expand-secret-name: rook-csi-cephfs-provisioner
  csi.storage.k8s.io/controller-expand-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.

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kubectl create -f deploy/examples/csi/cephfs/storageclass.yaml

Quotas

Attention

The CephFS CSI driver uses quotas to enforce the PVC size requested.

Only newer kernels support CephFS quotas (kernel version of at least 4.17). If you require quotas to be enforced and the kernel driver does not support it, you can disable the kernel driver and use the FUSE client. This can be done by setting CSI_FORCE_CEPHFS_KERNEL_CLIENT: false in the operator deployment (operator.yaml). However, it is important to know that when the FUSE client is enabled, there is an issue that during upgrade the application pods will be disconnected from the mount and will need to be restarted. See the upgrade guide for more details.

Consume the Shared Filesystem: K8s Registry Sample

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

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apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: cephfs-pvc
  namespace: kube-system
spec:
  accessModes:
  - ReadWriteMany
  resources:
    requests:
      storage: 1Gi
  storageClassName: rook-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:
            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:

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kubectl create -f deploy/examples/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 Filesystem: 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 filesystem in the toolbox pod. See the Direct Filesystem topic for more details.

Consume the Shared Filesystem across namespaces

A PVC that you create using the rook-cephfs storageClass can be shared between different Pods simultaneously, either read-write or read-only, but is restricted to a single namespace (a PVC is a namespace-scoped resource, so you cannot use it in another one).

However there are some use cases where you want to share the content from a CephFS-based PVC among different Pods in different namespaces, for a shared library for example, or a collaboration workspace between applications running in different namespaces.

You can do that using the following recipe.

Shared volume creation

  • In the rook namespace, create a copy of the secret rook-csi-cephfs-node, name it rook-csi-cephfs-node-user .
  • Edit your new secret, changing the name of the keys (keep the value as it is):
    • adminID -> userID
    • adminKey -> userKey
  • Create the PVC you want to share, for example:
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kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: base-pvc
  namespace: first-namespace
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 100Gi
  storageClassName: rook-cephfs
  volumeMode: Filesystem
  • The corresponding PV that is created will have all the necessary info to connect to the CephFS volume (all non-necessary information are removed here):
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kind: PersistentVolume
apiVersion: v1
metadata:
  name: pvc-a02dd277-cb26-4c1e-9434-478ebc321e22
  annotations:
    pv.kubernetes.io/provisioned-by: rook.cephfs.csi.ceph.com
  finalizers:
    - kubernetes.io/pv-protection
spec:
  capacity:
    storage: 100Gi
  csi:
    driver: rook.cephfs.csi.ceph.com
    volumeHandle: >-
      0001-0011-rook-0000000000000001-8a528de0-e274-11ec-b069-0a580a800213
    volumeAttributes:
      clusterID: rook
      fsName: rook-cephfilesystem
      storage.kubernetes.io/csiProvisionerIdentity: 1654174264855-8081-rook.cephfs.csi.ceph.com
      subvolumeName: csi-vol-8a528de0-e274-11ec-b069-0a580a800213
      subvolumePath: >-
        /volumes/csi/csi-vol-8a528de0-e274-11ec-b069-0a580a800213/da98fb83-fff3-485a-a0a9-57c227cb67ec
    nodeStageSecretRef:
      name: rook-csi-cephfs-node
      namespace: rook
    controllerExpandSecretRef:
      name: rook-csi-cephfs-provisioner
      namespace: rook
  accessModes:
    - ReadWriteMany
  claimRef:
    kind: PersistentVolumeClaim
    namespace: first-namespace
    name: base-pvc
    apiVersion: v1
    resourceVersion: '49728'
  persistentVolumeReclaimPolicy: Retain
  storageClassName: rook-cephfs
  volumeMode: Filesystem

  • On this PV, change the persistentVolumeReclaimPolicy parameter to Retain to avoid it from being deleted when you will delete PVCs. Don't forget to change it back to Delete when you want to remove the shared volume (see full procedure in the next section).

  • Copy the YAML content of the PV, and create a new static PV with the same information and some modifications. From the original YAML, you must:

    • Modify the original name. To keep track, the best solution is to append to the original name the namespace name where you want your new PV. In this example newnamespace.
    • Modify the volumeHandle. Again append the targeted namespace.
    • Add the staticVolume: "true" entry to the volumeAttributes.
    • Add the rootPath entry to the volumeAttributes, with the same content as subvolumePath.
    • In the nodeStageSecretRef section, change the name to point to the secret you created earlier, rook-csi-cephfs-node-user.
    • Remove the unnecessary information before applying the YAML (claimRef, managedFields,...):

Your YAML should look like this:

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kind: PersistentVolume
apiVersion: v1
metadata:
  name: pvc-a02dd277-cb26-4c1e-9434-478ebc321e22-newnamespace
spec:
  capacity:
    storage: 100Gi
  csi:
    driver: rook.cephfs.csi.ceph.com
    volumeHandle: >-
      0001-0011-rook-0000000000000001-8a528de0-e274-11ec-b069-0a580a800213-newnamespace
    volumeAttributes:
      clusterID: rook
      fsName: rook-cephfilesystem
      storage.kubernetes.io/csiProvisionerIdentity: 1654174264855-8081-rook.cephfs.csi.ceph.com
      subvolumeName: csi-vol-8a528de0-e274-11ec-b069-0a580a800213
      subvolumePath: >-
        /volumes/csi/csi-vol-8a528de0-e274-11ec-b069-0a580a800213/da98fb83-fff3-485a-a0a9-57c227cb67ec
      rootPath: >-
        /volumes/csi/csi-vol-8a528de0-e274-11ec-b069-0a580a800213/da98fb83-fff3-485a-a0a9-57c227cb67ec
      staticVolume: "true"
    nodeStageSecretRef:
      name: rook-csi-cephfs-node
      namespace: rook
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  storageClassName: rook-cephfs
  volumeMode: Filesystem
  • In a new or other namespace, create a new PVC that will use this new PV you created. You simply have to point to it in the volumeName parameter. Make sure you enter the same size as the original PVC!:
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kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: second-pvc
  namespace: newnamespace
  finalizers:
    - kubernetes.io/pvc-protection
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 100Gi
  volumeName: pvc-a02dd277-cb26-4c1e-9434-478ebc321e22-newnamespace
  storageClassName: rook-cephfs
  volumeMode: Filesystem

You have now access to the same CephFS subvolume from different PVCs in different namespaces. Redo the previous steps (copy PV with a new name, create a PVC pointing to it) in each namespace you want to use this subvolume.

Note: the new PVCs/PVs we have created are static. Therefore CephCSI does not support snapshots, clones, resizing or delete operations for them. If those operations are required, you must make them on the original PVC.

Shared volume removal

As the same CephFS volume is used by different PVCs/PVs, you must proceed very orderly to remove it properly.

  • Delete the static PVCs in the different namespaces, but keep the original one!
  • Delete the corresponding static PVs that should now have been marked as "Released". Again, don't delete the original one yet!
  • Edit the original PV, changing back the persistentVolumeReclaimPolicy from Retain to Delete.
  • Delete the original PVC. It will now properly delete the original PV, as well as the subvolume in CephFS.

Pending Issue

Due to this bug, the global mount for a Volume that is mounted multiple times on the same node will not be unmounted. This does not result in any particular problem, apart from polluting the logs with unmount error messages, or having many different mounts hanging if you create and delete many shared PVCs, or you don't really use them.

Until this issue is solved, either on the Rook or Kubelet side, you can always manually unmount the unwanted hanging global mounts on the nodes:

  • Log onto each node where the volume has been mounted.
  • Check for hanging mounts using their volumeHandle.
  • Unmount the unwanted volumes.

Teardown

To clean up all the artifacts created by the filesystem demo:

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kubectl delete -f kube-registry.yaml

To delete the filesystem components and backing data, delete the Filesystem CRD.

Warning

Data will be deleted if preserveFilesystemOnDelete=false.

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kubectl -n rook-ceph delete cephfilesystem myfs

Note: If the "preserveFilesystemOnDelete" filesystem attribute is set to true, the above command won't delete the filesystem. Recreating the same CRD will reuse the existing filesystem.

Advanced Example: Erasure Coded Filesystem

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