Docker Volume Driver for vSphere

OK, that’s all the constituent parts installed on both the hypervizor and VM. Let’s now see it in action.

4. Create volume for use by containers

In this example, I will create a 20GB VMDK called MyVolume, and use it as a persistent volume for a container running Ubuntu first, and then a container running Debian. First I must create the volume.

root@photon-machine [ ~ ]# docker volume create --driver=vmdk \
--name=MyVolume -o size=20gb
MyVolume

root@photon-machine [ ~ ]# docker volume ls
DRIVER              VOLUME NAME
vmdk                MyVolume
root@photon-machine [ ~ ]#

root@photon-machine [ ~ ]# docker volume inspect MyVolume
[
    {
        "Name": "MyVolume",
        "Driver": "vmdk",
        "Mountpoint": "/mnt/vmdk/MyVolume",
        "Labels": {}
    }
]
root@photon-machine [ ~ ]#

In this next step, I will run a container with an Ubuntu image, and pass the volume MyVolume to it for persistent storage. It should appear in the path /MyVolume in the container. Note: Do not provide the full mountpoint, just the name is required:

root@photon-machine [ ~ ]# docker run -it -v MyVolume:/MyVolume ubuntu bash
root@bd9410fb4c1d:/# ls
Myvolume  bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  \
root  run  sbin  srv  sys  tmp  usr  var
root@fe8c21d003fa:/# df
Filesystem                                      1K-blocks    Used Available Use% Mounted on
overlay                                           8122788 6095776   1591356  80% /
tmpfs                                             4085412       0   4085412   0% /dev
tmpfs                                             4085412       0   4085412   0% /sys/fs/cgroup
/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:0:0:0  20642428   44992  19548860   1% /MyVolume
/dev/root                                         8122788 6095776   1591356  80% /etc/hosts
shm                                                 65536       0     65536   0% /dev/shm
root@fe8c21d003fa:/#
root@bd9410fb4c1d:/# cd Myvolume/
root@bd9410fb4c1d:/Myvolume# ls
root@bd9410fb4c1d:/Myvolume#

At the moment the volume is empty. Let’s put some content in it.

root@bd9410fb4c1d:/Myvolume# mkdir Cormac
root@bd9410fb4c1d:/Myvolume# cd Cormac
root@bd9410fb4c1d:/Myvolume/Cormac# echo "Very important file that must \
persist" >> important
root@bd9410fb4c1d:/Myvolume/Cormac# ls
important
root@bd9410fb4c1d:/Myvolume/Cormac# cat important
Very important file that must persist
root@bd9410fb4c1d:/Myvolume/Cormac# exit
exit
root@photon-machine [ ~ ]#

We’ve added a little bit of content now, but we have also stopped the container. Just to show that the content persists, lets run another container and pass it the same volume, this time with a Debian image, and see if we can access the previously created content.

root@photon-machine [ ~ ]# docker run -it -v MyVolume:/MyVolume debian bash
Unable to find image 'debian:latest' locally
latest: Pulling from library/debian
51f5c6a04d83: Pull complete
a3ed95caeb02: Pull complete
Digest: sha256:978927d00fdd51a21dab7148aa8bbc704a69b518fa6a12aa8f45be3f03495860
Status: Downloaded newer image for debian:latest
root@348fd34de643:/# ls
Myvolume  bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  \
root  run  sbin  srv  sys  tmp  usr  var
root@348fd34de643:/# df
Filesystem                                      1K-blocks    Used Available Use% Mounted on
overlay                                           8122788 6095920   1591212  80% /
tmpfs                                             4085412       0   4085412   0% /dev
tmpfs                                             4085412       0   4085412   0% /sys/fs/cgroup
/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:0:0:0  20642428   44992  19548860   1% /MyVolume
/dev/root                                         8122788 6095920   1591212  80% /etc/hosts
shm                                                 65536       0     65536   0% /dev/shm
root@348fd34de643:/#
root@348fd34de643:/# cd Myvolume/ 
root@348fd34de643:/Myvolume# ls Cormac 
root@348fd34de643:/Myvolume# cd Cormac/ 
root@348fd34de643:/Myvolume/Cormac# ls 
important 
root@348fd34de643:/Myvolume/Cormac# cat important 
Very important file that must persist 
root@348fd34de643:/Myvolume/Cormac#

And there we have it. Containers using VMDKs on vSphere datastores to persist data. If you wanted to see what is created on the actual datastore at the ESXi host level, you can navigate to it as normal from the ESXi host. They are stored in a folder called dockvols:

[root@esxi-hp-08:/vmfs/volumes/562f4eef-04977492-d303-a0369f56ddc0/dockvols] ls -l
total 506880
-rw-------    1 root     root           173 Jun  3 06:50 MyVolume-6c182e87765678fb.vmfd
-rw-------    1 root     root     21474836480 Jun  3 06:51 MyVolume-flat.vmdk
-rw-------    1 root     root           564 Jun  3 06:50 MyVolume.vmdk
[root@esxi-hp-08:/vmfs/volumes/562f4eef-04977492-d303-a0369f56ddc0/dockvols]

Although this example only shows a local VMFS datastore being used for persistent storage, the docker volume driver for vSphere also works with shared VMFS, NFS and VSAN. I’ll try to revisit the VSAN implementation in a future post to see how it works with policies, etc.