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 supported 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 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>
Note
Before the Xena release, the image_source
field was also required:
--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>
Note
While this interface example utilizes a HTTP URL, as with all fields
referencing file artifacts in the instance_info
field, a user is
able to request a file path URL, or an HTTPS URL, or as a Glance Image
Service object UUID.
Warning
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 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>