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Revision as of 23:18, 24 March 2014 by Jim Rollenhagen (talk | contribs)


At the moment, Ironic uses exactly the same deployment ramdisk as the Nova baremetal driver does. The current deploy model exposes a hard drive via iSCSI. The conductor driver then mounts this volume and writes an OS image to it.

We believe that a deployment ramdisk should be able to do more than just expose an iSCSI volume. This ramdisk should have direct access to the hardware, and be able to:

  • Erase disks
  • Partition disks
  • Install bootloaders
  • Install an OS image
  • Update firmware
  • Configure RAID
  • And more...

Ironic-python-agent allows this functionality to be exposed to Ironic.

What is it?

  • The agent is a small python application that is meant to be embedded in a ramdisk.
  • The target machine boots this ramdisk, which starts the agent process.
  • The agent then exposes a REST API that Ironic uses to interact with the agent.
  • The API calls pluggable backends to interact with the machine.


The REST API will expose a set of fine-grained commands, such as "wipe disk" and "write image". The REST API will also expose an endpoint to send a list of commands to be run asynchronously. The agent will register as being on a given node, and get that node's UUID, on startup, by POSTing to the Ironic API The agent will heartbeat to Ironic on a given interval. All functionality, with the exception of the heartbeater and API, should be fully pluggable.

Sequence diagram of the agent mechanism (draw.io editable version)

Full Ironic system architecture when using the agent.

Pluggable Backends

Preliminary list of backends available:

  • Hardware (can handle both inventory and manipulation)
  • Provisioning (bootloader/imaging/configdrive)
  • This could maybe be split into separate drivers, but is not yet necessary.
  • Workflows - there are two pieces to this:
  • "Canned" workflows: A single endpoint that runs multiple tasks, defined by the driver. Example: a "deploy" endpoint.
  • Arbitrary workflows: A single endpoint that runs an arbitrary list of multiple tasks.

Agent driver

The Ironic conductor will run a driver corresponding to this agent. This driver will live in the Ironic tree as an official driver. This driver may eventually be merged into Ironic's PXE driver - it will depend how much is common between the two.