6.15. MicroKernel image

RackHD utilizes RancherOS booted in RAM and a customized docker image run in RancherOS to perform various operations such as node discovery and firmware management.

The on-imagebuilder repository contains a set of scripts that uses Docker to build docker images that run in RancherOS, primarily for use with the on-taskgraph workflow engine.

6.15.1. Requirements

  • Docker

6.15.2. Bootstrap Process

The images produced by these scripts are intended to be netbooted and run in RAM. The typical flow for how these images are used/booted is this:

  • Netboot RacherOS (kernel and initrd) via PXE/iPXE
  • The custom cloud-config file requests a rackhd/micro docker image from the boot server.
  • It then starts a container with full container capabilities using the rackhd/micro docker image.

6.15.3. Building Images

Instructions for building images, can be found in the on-imagebuilder README.

6.15.4. How To Login Microkernel

By default, RackHD has a workflow to let users login RancherOS based microkernel to debug. The workflow name is Graph.BootstrapRancher.

curl -X POST -H 'Content-Type: application/json' <server>/api/current/nodes/<identifier>/workflows?name=Graph.BootstrapRancher

When this workflow is running, it will set node to PXE boot, then reboot the node. The node will boot into microkernel, finally you could SSH login node’s microkernel from the RackHD server. The node’s IP address could be retrieved from ‘GET /lookups’ API like below, the SSH username:password is rancher:monorail.

curl <server>/api/current/lookups?q=<identifier>