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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.

Configuration

Ramdisk/ISO boot requires using the ramdisk deploy interface. As with most non-default interfaces, it must be enabled and set for a node to be utilized:

[DEFAULT]
...
enabled_deploy_interfaces = iscsi,direct,ramdisk
...

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

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

or update an existing node:

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

Using virtual media:

openstack baremetal node create --driver redfish \
    --deploy-interface ramdisk \
    --boot-interface redfish-virtual-media

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

Note

The requirement to pass image_source is artificial and will be fixed in a future version of the Bare Metal service.

Booting an ISO

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

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

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: