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CVMFS DaemonSet for Kubernetes

CVMFS provides a scalable, global, read-only filesystem that is developed at CERN and used at many computing centers to distribute software. This repository contains manifests that can be used by a Kubernetes administrator to make CVMFS mounts available to pods running inside the cluster.

There are two pieces required to add support:

  1. A CVMFS DaemonSet, a set of pods that runs on every host in the cluster. The CVMFS processes are run inside these pods and the FUSE filesystem mount is bind-mounted into the host filesystem.
  2. A set of PersistentVolumes that permit bind-mounting the read-only host filesystem into user's pods. This must be setup once per namespace.

Both items require significant administrator privileges to setup as they require the ability to view the host filesystem inside the container.

An arbitrary number of pods in the same namespace can mount a persistent volume. Accordingly, step 2 must be performed once for each namespace where CVMFS is used.

CVMFS DaemonSet

The CVMFS DaemonSet is provided by the cvmfs-daemonset directory in this repository. It can be loaded with the following command:

kubectl apply -k cvmfs-daemonset

If you are using Kustomize at your site already, you can add incorporate these lines to your kustomization.yaml

bases:
- github.com/opensciencegrid/osg-k8s-cvmfs/cvmfs-daemonset?ref=main

Note this additionally starts a Squid deployment to handle the caching of HTTP requests to the wider system.

Persistent Volumes

The persistent volumes can be installed into the CVMFS namespace with the following command:

kubectl apply -k cvmfs-pvcs

However, this only installs persistent volumes and the corresponding claims into the cvmfs namespace. You can utilize kustomize overlays to create these claims across many namespaces.

Setup a directory with a kustomization.yaml for each namespace where you want CVMFS:

/
  /namespace1/
    /namespace1/kustomization.yaml
  /namespace2/
    /namespace2/kustomization.yaml

The kustomization.yaml file for namespace1 will look like this:

namespace: namespace1

namePrefix: namespace1-

bases:
- github.com/opensciencegrid/osg-k8s-cvmfs/cvmfs-pvcs?ref=main

Then, CVMFS can be added to the namespace with the following command:

kubectl apply -k namespace1

Deployment Notes for Rancher

This solution requires the kubelet process to have access to a specific directory on the host (so the CVMFS pod can mount the FUSE filesystem as read-only and the other pods can mount this filesystem). Some distributions of Kubernetes, like Rancher, launch kubelet itself inside a Docker container, breaking the underlying assumption.

To make /var/lib/cvmfs-k8s available to Rancher, from Rancher's web UI, add the following kubelet configuration:

kubelet:
    image: ""
    extra_args: {}
    extra_binds:
      - "/var/lib/cvmfs-k8s:/var/lib/cvmfs-k8s:rshared"

Original Author

This code was originally authored by Igor Sfiligoi for the Pacific Research Platform.