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.

Configuration

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:

[DEFAULT]
...
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
<redfish-virtual-media-ramdisk> 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:

• openssh-server
  to install the SSH server since it’s not provided by default by some
  minimal images.
• devuser
  or dynamic-login
  to provide SSH access.
• dhcp-all-interfaces
  or simple-init
  to configure networking.

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>

--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>

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
following:

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.

Limitations

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
caveats:

• 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

Disable
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
Never:

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