Qlustar

The stationary CompFlu infrastructure (HPC cluster nodes, workstations) is using Qlustar as an operating system with central management for distributed functionality (user accout management, package management/updates, queueing, networking, …). Qlustar is developed and maintained by the company Q-Leap, contact: Roland Fehrenbacher.

Qlustar is a relatively shallow spin-off of Ubuntu LTS (22.04 as of 2023-06). It is using most of Ubuntu for everyday tasks, and adds on top a distributed mangagement layer, QluMan, that takes care of keeping machines in sync with their intended state.

Filesystem design & quirks

Qlustar is designed around the aim of a streamlined provisioning of OSes to diskless clients, with good scaling and optimized network load, rather than being configurable in a transparent and logical manner.

The bottom-most layer of the OS is packaged as images, that is, the root filesystem is cut into chunks of squashfs archives and sent to clients early in the boot process. Images are located on the head node at /var/lib/qlustar/images/ and are being taken care of by Q-Leap.

This means, however, that management of packages and configuration is not independent from external interaction. On clients, the root file system is assembled from the following layers:

  • Image, loaded into RAM at boot time. If updates are needed, they have to be arranged with Q-Leap
  • NFS root (chroot), a file system overlay with low priority (changes are overwritten by the image). apt is in a functional state there, go there to install extra packages. Multiple chroots are present, to enter the chroot $CHROOT, the head node provides the shortcut chroot-$CHROOT.
  • Overwriting files in the images happens by root FS overlays. These are selected in QluMan, and are located on the head node at /var/lib/qlustar/root-fs/
  • Since root FS overlays happen rather late in the boot process, there is the need for boot-time customizations. These are shell scripts that are executed prior to starting systemd units, necessary for patching existing configuration files. Find these at /etc/qlustar/common/rc.boot/.

See also https://docs.qlustar.com/Qlustar/13/ClusterOS/administration-manual/node-manage/customize.html

  • compflu/backstage/qlustar.txt
  • Last modified: 2023-05-30 12:12
  • by j.hielscher