Documentation

    PLEASE NOTE: This document applies to v0.7 version and not to the latest stable release v1.1

    Documentation for other releases can be found by using the version selector in the left bottom of any doc page.

    Shared File System

    A shared file system can be mounted read-write 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

    Create the File System

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

    Save this shared file system definition as rook-filesystem.yaml:

    apiVersion: rook.io/v1alpha1
    kind: Filesystem
    metadata:
      name: myfs
      namespace: rook
    spec:
      metadataPool:
        replicated:
          size: 3
      dataPools:
        - erasureCoded:
           dataChunks: 2
           codingChunks: 1
      metadataServer:
        activeCount: 1
        activeStandby: true
    

    Now let’s create the file system. 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 rook-filesystem.yaml
    
    # To confirm the file system is configured, wait for the mds pods to start
    kubectl -n rook get pod -l app=rook-ceph-mds
    

    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
    

    Consume the file system

    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: ReplicationController
    metadata:
      name: kube-registry-v0
      namespace: kube-system
      labels:
        k8s-app: kube-registry
        version: v0
        kubernetes.io/cluster-service: "true"
    spec:
      replicas: 3
      selector:
        k8s-app: kube-registry
        version: v0
      template:
        metadata:
          labels:
            k8s-app: kube-registry
            version: v0
            kubernetes.io/cluster-service: "true"
        spec:
          containers:
          - name: registry
            image: registry:2
            resources:
              limits:
                cpu: 100m
                memory: 100Mi
            env:
            - name: REGISTRY_HTTP_ADDR
              value: :5000
            - name: REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY
              value: /var/lib/registry
            volumeMounts:
            - name: image-store
              mountPath: /var/lib/registry
            ports:
            - containerPort: 5000
              name: registry
              protocol: TCP
          volumes:
          - name: image-store
            flexVolume:
              driver: rook.io/rook
              fsType: ceph
              options:
                fsName: myfs # name of the filesystem specified in the filesystem CRD.
                clusterName: rook # namespace where the Rook cluster is deployed
                # by default the path is /, but you can override and mount a specific path of the filesystem by using the path attribute
                # path: /some/path/inside/cephfs
    

    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.

    Test the storage

    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.

    Start and connect to the Rook toolbox.

    # Mount the same filesystem that the kube-registry is using
    mkdir /tmp/registry
    rookctl filesystem mount --name myfs --path /tmp/registry
    
    # If you have pushed images to the registry you will see a directory called docker
    ls /tmp/registry
    
    # Cleanup the filesystem mount
    rookctl filesystem unmount --path /tmp/registry
    rmdir /tmp/registry
    

    Teardown

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

    kubectl -n kube-system delete secret rook-admin
    kubectl delete -f kube-registry.yaml