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xCAT, the Bare-Metal Provisioner

xCAT is complete solution for bare metal provisioning for High-Performance Computing clusters.

Architecture​

The architecture is the following:

Xcat-arch

xCAT Management Node is deployed as a container and runs multiple network services responsible for the provisioning of bare-metal systems.

xCAT is also able to have "slaves" named Service Node.

The Service Processor (SP) controls the hardware and is used to perform out-of-band hardware control (e.g. Integrated Management Module (IMM), Flexible Service Processor (FSP), Baseboard Management Controller (BMC), etc).

The Service Processor is connected to xCAT via the Service Network.

The Management Network is used for OS provisioning (via xNBA or PXE).

Why xCAT ?​

Our main criteria for choosing a bare metal provisioning solution is:

  • Operating system image management: provisioning methods, supported operating systems, ease of use.
  • BMC configuration (IPMI, HMC, FSP, OpenBMC)
  • Configuration management (Declarative, post-boot scripts, backups, ...)

While a lot of solutions exist for bare-metal provisioning like OpenStack Ironic or MAAS, only a few are able to do disk-less provisioning.

Disk-less (or Stateless) provisioning is based on an OverlayFS root, with the OS being loaded from a SquashFS image. The OverlayFS is mounted as a tmpfs, that is, in the RAM.

upper-lower

Since the root is mounted in RAM, restarting a node will "clean it up", similar to a Docker container.

With OverlayFS, we follow a proper DevOps practice where the architecture is immutable and mutable data is stored on disks.

Moreover, we are not only looking for a well-maintained open-source project, but also an easy-to-use solution.

We were interested in Grendel because it promises to be better than xCAT, but it is still too young and its documentation is not yet perfect. xCAT is 23 years old, is still maintained by iBM and has every functionality for bare metal provisioning.

While xCAT is not friendly to GitOps or Kubernetes, we plan to develop a way to configure xCAT declaratively from Kubernetes (probably by developing a Kubernetes Operator, or by applying the stanza file at the boot of container).

For now, the only way to use xCAT is to connect via SSH to your server.