CVMFS is a software distribution service, it is used by High Energy Physics experiments at CERN to synchronize software environments across the whole collaborations.

In the context of a Kubernetes + JupyterHub deployment on Jetstream, for example deployed using Magnum following my tutorial, it is useful to use CVMFS to make the software tools of a collaboration to all the users connected to JupyterHub, so that we can keep the base Docker image simpler and smaller.

Alternatives

A already existing solution is the CVMFS CSI driver, however it doesn’t have much documentation, so I haven’t tested it. It would be useful for larger deployments, but we are designing for a 5 (possibly up to 10) nodes Kubernetes cluster.

Architecture

We have a pod running in Kubernetes (running as a privileged Docker container) which runs the CVMFS client and caches locally (on a dedicated Openstack volume) some pre-defined CVMFS repositories (at the moment we do not support automounting).

Currently we are using the DIRECT connection for the CVMFS client, due to having just a single client which accesses a small amount of data. Using a proxy is required instead for heavier usage, and it could also be deployed inside Kubernetes.

The same pod also runs a NFS server and exposes it internally into the Kubernetes cluster, over the local Jetstream network, to any other pod which can use a NFS volume and mount it to the /cvmfs folder inside the container. We also activate the CVMFS configuration options for NFS support, following the documentation.

Deployment

The repositories used in this deployment are:

First we need to checkout the jupyterhub-deploy-kubernetes-jetstream repository:

git clone https://github.com/zonca/jupyterhub-deploy-kubernetes-jetstream.git
cd jupyterhub-deploy-kubernetes-jetstream/cvmfs

Then configure the CVMFS pod with the required repositories, see the CVMFS_REPOSITORIES variable in pod_cvmfs_nfs.yaml.

Then deploy the pod with:

kubectl create -f pod_cvmfs_nfs.yaml

This creates 2 Openstack volumes, a 20 GB volume for the CVMFS cache, and a 1 GB volume which is just necessary as the /cvmfs root folder of the NFS server. It also creates the nfs-service Service, with a fixed IP, so that we can use it in the pod using this.

Finally we can create a pod using mounting the folder via NFS:

kubectl create -f test_nfs_mount.yaml

Then get a terminal in the pod with:

bash ../terminal_pod.sh test-nfs-mount

This creates a volume which mounts the /cvmfs folder shared with NFS, this automatically also shares also all the subfolders.

Finally we can check the content of the /cvmfs folder.