Override PXE options via Glance property
The proposal presents the work required to allow PXE boot an image using a specific kernel command line for that image. Change-Id: I9371394eb1fd90ed52bf8de82e6f53a9c135f244
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Lucas Alvares Gomes
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specs/liberty/override-pxe-options-via-glance-property.rst
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specs/liberty/override-pxe-options-via-glance-property.rst
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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========================================
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Override PXE options via Glance property
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========================================
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https://blueprints.launchpad.net/ironic/+spec/override-pxe-options-via-glance-property
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The proposal presents the work required to allow PXE boot an image using
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a specific kernel command line for that image.
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Problem description
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===================
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Some images requires having specific kernel command line to boot
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correctly. Currently, Ironic tries to determine things like the root
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filesystem the image is on ("root=" kernel command line) by getting the
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UUID of the image filesystem and setting as the root= parameter. This is
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not correct for all images because some may need to boot from a different
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root filesystem, e.g:
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* The device path of its LVM volume [root=/dev/mapper/vg-lv_root]
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* From one squashfs filesystem [root=live:<path>]
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* A btrfs subvolume [root=/dev/disk/by-uuid/<UUID of btrfs-root>]
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As a real example, the Fedora Atomic uses ``lvm`` and ``ostree``. It
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requires a kernel command line as the example below to boot properly::
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nofb nomodeset vga=normal console=tty1 no_timer_check
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rd.lvm.lv=atomicos/root root=/dev/mapper/atomicos-root
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ostree=/ostree/boot.0/fedora-atomic/a002a2c2e44240db614e09e82c/0
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Proposed change
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===============
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In the same way Ironic look at the Glance image properties to find out the
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Glance UUID for the image's kernel and ramdisk (kernel_id and ramdisk_id)
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and populate the node's ``instance_info`` field with the ``kernel`` and
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``ramdisk`` keys.
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This spec propose having a new image's property field called
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``kernel_cmdline`` that Ironic will look at, and if present, it will
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populate the node's ``instance_info`` field with a ``kernel_cmdline``
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key.
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If the ``instance_info.kernel_cmdline`` is populate Ironic will skip
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getting the root partition filesystem UUID and will use the command
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line from the ``instance_info`` field instead of the default one in
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the template. It's important to note that the values present at the
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``pxe_append_params`` configuration option will still be appended at
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the end of the image's custom kernel command line by Ironic.
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Setting the keys in the ``instance_info`` field is important because
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it also allows Ironic to operate in standalone mode without Glance.
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Alternatives
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------------
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Always use whole disk images when deploying images that requires a
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specific kernel command line
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Data model impact
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-----------------
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None
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State Machine Impact
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--------------------
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None
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REST API impact
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---------------
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None
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RPC API impact
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--------------
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None
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Driver API impact
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-----------------
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None
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Nova driver impact
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------------------
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None
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Security impact
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---------------
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None
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Other end user impact
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---------------------
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None
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Scalability impact
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------------------
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None
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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Deployers that wants to deploy an image with a specific kernel command
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line should know and set it in Glance image's property prior to trying
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to boot the image.
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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lucasagomes <lucasagomes@gmail.com>
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Other contributors:
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None
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Work Items
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----------
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* Make Ironic look at the ``kernel_cmdline`` image property in Glance
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and if present set it to the node's ``instance_info`` field
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* When preparing to boot the user's image, make Ironic check if the
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node's ``instance_info`` field contains a key called ``kernel_cmdline``
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(along with ``kernel_id`` and ``ramdisk_id``) and if so, use that kernel
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command line to boot the image.
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Dependencies
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============
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None
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Testing
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=======
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* Unit Tests
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Upgrades and Backwards Compatibility
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====================================
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None
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Documentation Impact
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====================
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The Ironic deploy documentation will be updated to reflect the changes
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made by this spec.
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References
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==========
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* `Kernel parameters <https://www.kernel.org/doc/Documentation/kernel-parameters.txt>`_
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* `Project atomic <http://www.projectatomic.io>`_
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