Map a RBD device inside a Docker container

People have been having trouble to map a RBD device in a container. Quick tip on how to map a Rados Block Device into a container.

Bootstrap a Ceph demo container:

$ docker run -d \
--net=host \
-v /var/lib/ceph:/var/lib/ceph \
-v /etc/ceph:/etc/ceph \
-e MON_IP=192.168.0.1 \
-e CEPH_NETWORK=192.168.0.0/24 \
ceph/demo

Enable the Kernel module and create the image:

$ sudo modprobe rbd
$ sudo rbd create foo -s 1024

Then bootstrap a container, map the container and put a filesystem on top of it:

$ sudo docker run -ti -v /dev:/dev -v /sys:/sys --net=host --privileged=true -v /etc/ceph:/etc/ceph ceph/base bash
[email protected]:/# rbd map foo
/dev/rbd0

[email protected]:/# rbd showmapped
id pool image snap device
0 rbd foo - /dev/rbd0

[email protected]:/# mkfs.ext4 /dev/rbd0
...
...

[email protected]:/# mount /dev/rbd0 /mnt/

[email protected]:/# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/dm-5 10G 483M 9.6G 5% /
shm 1001M 8.0K 1001M 1% /dev/shm
tmpfs 1001M 12K 1001M 1% /run
tmpfs 1001M 0 1001M 0% /tmp
devtmpfs 986M 0 986M 0% /dev
tmpfs 1001M 8.0K 1001M 1% /dev/shm
/dev/mapper/atomicos-root 11G 1.9G 9.1G 18% /etc/ceph
tmpfs 1001M 0 1001M 0% /sys/fs/cgroup
/dev/rbd0 976M 1.3M 908M 1% /mnt


Et voilà !

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