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
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:
[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 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.
The resulting files (
/output/ramdisk.initramfs in this case) can then be used when Booting a
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 required:
Booting an ISO¶
ramdisk deploy interface can also be used to boot an ISO image.
baremetal node set <NODE> \ --instance-info boot_iso=http://path/to/boot.iso baremetal node deploy <NODE>
This feature, when utilized with the
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
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 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.
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_argumentsparameter 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.
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
driver_info. Which can be set to
$ openstack baremetal node set --driver-info force_persistent_boot_device='Never' <node>