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Taikun OCP Guide

Table of Contents

Booting a Ramdisk or an ISO

Ironic supports booting a user provided ramdisk or an ISO image
(starting with the Victoria release) instead of deploying a node. Most
commonly this is performed when an instance is booted via PXE, iPXE or
Virtual Media, with the only local storage contents being those in
memory. It is suported by pxe, ipxe,
redfish-virtual-media and ilo-virtual-media
boot interfaces.


Ramdisk/ISO boot requires using the ramdisk deploy
interface. It is enabled by default starting with the Zed release cycle.
On an earlier release, it must be enabled explicitly:

enabled_deploy_interfaces = direct,ramdisk

Once enabled and the conductor(s) have been restarted, the interface
can be set upon creation of a new node:

baremetal node create --driver ipmi \
    --deploy-interface ramdisk \
    --boot-interface ipxe

or update an existing node:

baremetal node set <NODE> --deploy-interface ramdisk

You can also use it with redfish virtual media
instead of iPXE.

Creating a ramdisk

A ramdisk can be created using the ironic-ramdisk-base
element from ironic-python-agent-builder,
e.g. with Debian:

export ELEMENTS_PATH=/opt/stack/ironic-python-agent-builder/dib
disk-image-create -o /output/ramdisk \
    debian-minimal ironic-ramdisk-base openssh-server dhcp-all-interfaces

You should consider using the following elements:

The resulting files (/output/ramdisk.kernel and
/output/ramdisk.initramfs in this case) can then be used
when Booting a ramdisk.

Booting a ramdisk

Pass the kernel and ramdisk as normally, also providing the ramdisk
as an image source, for example,

baremetal node set <NODE> \
    --instance-info kernel=http://path/to/ramdisk.kernel \
    --instance-info ramdisk=http://path/to/ramdisk.initramfs
baremetal node deploy <NODE>


Before the Xena release, the image_source field was also

--instance-info image_source=http://path/to/ramdisk.initramfs

Booting an ISO

The ramdisk deploy interface can also be used to boot an
ISO image. For example,

baremetal node set <NODE> \
    --instance-info boot_iso=http://path/to/boot.iso
baremetal node deploy <NODE>


This feature, when utilized with the ipxe
boot_interface, will only allow a kernel and ramdisk to be
booted from the supplied ISO file. Any additional contents, such as
additional ramdisk contents or installer package files will be
unavailable after the boot of the Operating System. Operators wishing to
leverage this functionality for actions such as OS installation should
explore use of the standard ramdisk
deploy_interface along with the
instance_info/kernel_append_params setting to pass
arbitrary settings such as a mirror URL for the initial ramdisk to load
data from. This is a limitation of iPXE and the overall boot process of
the operating system where memory allocated by iPXE is released.

By default the Bare Metal service will cache the ISO locally and
serve from its HTTP server. If you want to avoid that, set the

baremetal node set <NODE> \
    --instance-info ramdisk_image_download_source=http

ISO images are also cached across deployments, similarly to how it is
done for normal instance images. The URL together with the last modified
response header are used to determine if an image needs updating.


The intended use case is for advanced scientific and ephemeral
workloads where the step of writing an image to the local storage is not
required or desired. As such, this interface does come with several

  • Configuration drives are not supported with network boot, only with
    Redfish virtual media.
  • Disk image contents are not written to the bare metal node.
  • Users and Operators who intend to leverage this interface should
    expect to leverage a metadata service, custom ramdisk images, or the
    instance_info/ramdisk_kernel_arguments parameter to add
    options to the kernel boot command line.
  • When using PXE/iPXE boot, bare metal nodes must continue to have
    network access to PXE and iPXE network resources. This is contrary to
    most tenant networking enabled configurations where this access is
    restricted to the provisioning and cleaning networks
  • As with all deployment interfaces, automatic cleaning of the node
    will still occur with the contents of any local storage being wiped
    between deployments.

Common options

persistent boot device for ramdisk iso boot

For iso boot, Ironic sets the boot target to continuously boot from
the iso attached over virtual media. This behaviour may not always be
desired e.g. if the vmedia is installing to hard drive and then
rebooting. In order to instead set the virtual media to be one time boot
Ironic provides the force_persistent_boot_device flag in
the node’s driver_info. Which can be set to

$ openstack baremetal node set --driver-info force_persistent_boot_device='Never' <node>