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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. It is enabled
by default starting with the Zed release cycle. On an earlier release, it must
be enabled explicitly:
.. code-block:: ini
[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:
.. code-block:: shell
baremetal node create --driver ipmi \
--deploy-interface ramdisk \
--boot-interface ipxe
or update an existing node:
.. code-block:: shell
baremetal node set <NODE> --deploy-interface ramdisk
You can also use it with :ref:`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:
.. code-block:: shell
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,
.. code-block:: shell
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,
.. code-block:: shell
baremetal node set <NODE> \
--instance-info boot_iso=http://path/to/boot.iso
baremetal node deploy <NODE>
.. 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:
.. code-block:: shell
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>
.. _ironic-python-agent-builder: https://opendev.org/openstack/ironic-python-agent-builder
.. _openssh-server: https://docs.openstack.org/diskimage-builder/latest/elements/openssh-server/README.html
.. _devuser: https://docs.openstack.org/diskimage-builder/latest/elements/devuser/README.html
.. _dynamic-login: https://docs.openstack.org/diskimage-builder/latest/elements/dynamic-login/README.html
.. _dhcp-all-interfaces: https://docs.openstack.org/diskimage-builder/latest/elements/dhcp-all-interfaces/README.html
.. _simple-init: https://docs.openstack.org/diskimage-builder/latest/elements/simple-init/README.html
|
