Live Git Flexvolume for Kubernetes

Flexvolume driver for Git repos that should track updates to the mounted repo.

Installing

This Flexvolume driver is a bash script that makes use of binaries installed on the Kubernetes nodes.

Installing the script itself is done simply as;

VOLUME_PLUGIN_DIR="/usr/libexec/kubernetes/kubelet-plugins/volume/exec"
mkdir -p "$VOLUME_PLUGIN_DIR/ananace~git-live"
cd "$VOLUME_PLUGIN_DIR/ananace~git-live"
curl -L -O https://raw.githubusercontent.com/ananace/flexvolume-git-live/master/git-live
chmod 755 git-live

The git-live script requires a couple of tools to be installed on all the nodes where it's to be used, additionally it currently requires systemd for launching the background updates;

• awk
• base64
• git
• grep
• jq
• realpath
• sha256sum

Running

Once the Flexvolume plugin has been installed on all relevant nodes, running it is as simple as creating a Kubernetes pod that will use it for a volume;

apiVersion: v1
kind: Pod
metadata:
  name: git-example
spec:
  containers:
  - name: busybox
    image: busybox
    command:
      - sh
      - -c
      - |
        ls -l /data
        tail -f /data/README.md
    volumeMounts:
    - name: data
      mountPath: /data
  volumes:
  - name: data
    flexVolume:
      driver: ananace/git-live
      options:
        repo: https://github.com/ananace/flexvolume-git-live
        interval: 5d
      readOnly: true

This example pod will check out the flexvolume sources and then actively print any new lines as they are added to the README file and pushed.

The interval argument is handled in the same manner as systemd.time timespans. The default interval - if not specified - can be set in the git-live script as DEFAULT_INTERVAL_SEC, and is by default set to 15 minutes.

Caveats

Due to the fact that checkouts are done as root on the underlying system, the git index has been moved away from the repository itself. This unfortunately means that tools inside the running pod will not be able to retrieve any data from the index of the git mount.

Currently, there's no way to differentiate read-only and read-write, the background updates will always override any user changes on every interval.

If you only require a static git checkout that doesn't follow any new commits, the Kubernetes documentation provides a better route.