Shared File System Quickstart

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