Reference:

http://rackhd.readthedocs.io/en/latest/devguide/debugging_guide.html#discovery-with-a-default-workflow

• Customize user-class in ipxe: https://github.com/RackHD/on-imagebuilder/blob/a5cf04d918244693b98d76fa48e34163fdb51a41/roles/ipxe/files/default.ipxe
• Two steps DHCP request, firstly get 'monorail-undionly.ipxe', then the ipxe will be boot and the /profiles API request https://github.com/RackHD/on-dhcp-proxy/blob/master/lib/message-handler.js#L176
• The entry point of /profiles API: https://github.com/RackHD/on-http/blob/master/lib/api/2.0/profiles.js#L34
  • First it will call /profiles without mac address, RackHD will send redirect.ipxe.
  • Secondaly, it will call /profiles with macAddress, the returned profiles is defined in bootstrap microkernel task: https://github.com/RackHD/on-tasks/blob/master/lib/task-data/tasks/bootstrap-ubuntu.js#L18
• The microkernel stuff are specified in linux.ipxe: https://github.com/RackHD/on-http/blob/master/data/profiles/linux.ipxe
• The microkernel will run bootstrap.js automatically: https://github.com/RackHD/on-imagebuilder/blob/a5cf04d918244693b98d76fa48e34163fdb51a41/common/files/rc.local#L46
• all discoveries task are defined in: https://github.com/RackHD/on-taskgraph/blob/master/lib/graphs/discovery-sku-graph.js
• Run sku specified graph: https://github.com/RackHD/on-taskgraph/blob/master/lib/graphs/discovery-sku-graph.js#L174