Direct Tools

Rook is designed with Kubernetes design principles from the ground up. This topic is going to escape the bounds of Kubernetes storage and show you how to use block and file storage directly from a pod without any of the Kubernetes magic. The purpose of this topic is to help you quickly test a new configuration, although it is not meant to be used in production. All of the benefits of Kubernetes storage including failover, detach, and attach will not be available. If your pod dies, your mount will die with it.

Start the Direct Mount Pod

To test mounting your Ceph volumes, start a pod with the necessary mounts. An example is provided in the examples test directory:

kubectl create -f cluster/examples/kubernetes/ceph/direct-mount.yaml

After the pod is started, connect to it like this:

kubectl -n rook-ceph get pod -l app=rook-direct-mount
$ kubectl -n rook-ceph exec -it <pod> bash

Block Storage Tools

After you have created a pool as described in the Block Storage topic, you can create a block image and mount it directly in a pod. This example will show how the Ceph rbd volume can be mounted in the direct mount pod.

Create the Direct Mount Pod.

Create a volume image (10MB):

rbd create replicapool/test --size 10
rbd info replicapool/test

# Disable the rbd features that are not in the kernel module
rbd feature disable replicapool/test fast-diff deep-flatten object-map

Map the block volume and format it and mount it:

# Map the rbd device. If the Direct Mount Pod was started with "hostNetwork: false" this hangs and you have to stop it with Ctrl-C,
# however the command still succeeds; see https://github.com/rook/rook/issues/2021
rbd map replicapool/test

# Find the device name, such as rbd0
lsblk | grep rbd

# Format the volume (only do this the first time or you will lose data)
mkfs.ext4 -m0 /dev/rbd0

# Mount the block device
mkdir /tmp/rook-volume
mount /dev/rbd0 /tmp/rook-volume

Write and read a file:

echo "Hello Rook" > /tmp/rook-volume/hello
cat /tmp/rook-volume/hello

Unmount the Block device

Unmount the volume and unmap the kernel device:

umount /tmp/rook-volume
rbd unmap /dev/rbd0

Shared Filesystem Tools

After you have created a filesystem as described in the Shared Filesystem topic, you can mount the filesystem from multiple pods. The the other topic you may have mounted the filesystem already in the registry pod. Now we will mount the same filesystem in the Direct Mount pod. This is just a simple way to validate the Ceph filesystem and is not recommended for production Kubernetes pods.

Follow Direct Mount Pod to start a pod with the necessary mounts and then proceed with the following commands after connecting to the pod.

# Create the directory
mkdir /tmp/registry

# Detect the mon endpoints and the user secret for the connection
mon_endpoints=$(grep mon_host /etc/ceph/ceph.conf | awk '{print $3}')
my_secret=$(grep key /etc/ceph/keyring | awk '{print $3}')

# Mount the filesystem
mount -t ceph -o mds_namespace=myfs,name=admin,secret=$my_secret $mon_endpoints:/ /tmp/registry

# See your mounted filesystem
df -h

Now you should have a mounted filesystem. If you have pushed images to the registry you will see a directory called docker.

ls /tmp/registry

Try writing and reading a file to the shared filesystem.

echo "Hello Rook" > /tmp/registry/hello
cat /tmp/registry/hello

# delete the file when you're done
rm -f /tmp/registry/hello

Unmount the Filesystem

To unmount the shared filesystem from the Direct Mount Pod:

umount /tmp/registry
rmdir /tmp/registry

No data will be deleted by unmounting the filesystem.