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ironic
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Merge "[doc-only] Add BFV basic flow and networking context"

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Zuul 2021-02-24 13:39:24 +00:00 committed by Gerrit Code Review
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doc/source/admin/boot-from-volume.rst
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@ -14,6 +14,60 @@ The boot from volume is supported on both legacy BIOS and
UEFI (iPXE binary for EFI booting) boot mode. We need to perform with
suitable images which will be created by diskimage-builder tool.
How this works - From Ironic's point of view
--------------------------------------------
In essence, ironic sets the stage for the process, by providing the required
information to the boot interface to facilitate the configuration of the
the node OR the iPXE boot templates such that the node CAN be booted.
.. seqdiag::
:scale: 80
diagram {
User; API; Conductor; Storage; Boot; Network; Deploy;
activation = none;
span_height = 1;
edge_length = 250;
default_note_color = white;
default_fontsize = 14;
User -> API [label = "User or intermediate service such as nova supplies volume target configuration."];
User -> API [label = "Sends deployment request."];
API -> Conductor [label = "API transmits the action to the conductor service"];
Conductor -> Storage [label = "Conductor calls the storage_interface to perform attachment of volume to node"];
Conductor -> Boot [label = "Conductor calls the boot interface signaling preparation of an instance"];
Conductor -> Network [label = "Conductor attaches the machine to network requested by the user VIF"];
Conductor -> Deploy [label = "Conductor starts deployment steps which just turn the power on."];
}
In this example, the boot interface does the heavy lifting. For drivers the
``irmc`` and ``ilo`` hardware types with hardware type specific boot
interfaces, they are able to signal via an out of band mechanism to the
baremetal node's BMC that the integrated iSCSI initiators are to connect
to the supplied volume target information.
In most hardware this would be the network cards of the machine.
In the case of the ``ipxe`` boot interface, templates are created on disk
which point to the iscsi target information that was either submitted
as part of the volume target, or when integrated with Nova, what was
requested as the baremetal's boot from volume disk upon requesting the
instance.
In terms of network access, both interface methods require connectivity
to the iscsi target. In the vendor driver specific path, additional network
configuration options may be available to allow separation of standard
network traffic and instance network traffic. In the iPXE case, this is
not possible as the OS userspace re-configures the iSCSI connection
after detection inside the OS ramdisk boot.
An iPXE user *may* be able to leverage multiple VIFs, one specifically
set to be set with ``pxe_enabled`` to handle the initial instance boot
and back-end storage traffic where as external facing network traffic
occurs on a different interface. This is a common pattern in iSCSI
based deployments in the physical realm.
Prerequisites
=============
Currently booting from a volume requires: