Boot interfaces

Boot interfaces

The boot interface manages booting of both the deploy ramdisk and the user instances on the bare metal node.

The PXE boot interface is generic and works with all hardware that supports booting from network. Alternatively, several vendors provide virtual media implementations of the boot interface. They work by pushing an ISO image to the node’s management controller, and do not require either PXE or iPXE. Check your driver documentation at Drivers, Hardware Types and Hardware Interfaces for details.

PXE boot

The pxe boot interface uses PXE or iPXE to deliver the target kernel/ramdisk pair. PXE uses relatively slow and unreliable TFTP protocol for transfer, while iPXE uses HTTP. The downside of iPXE is that it’s less common, and usually requires bootstrapping using PXE first.

The pxe boot interface works by preparing a PXE/iPXE environment for a node on the file system, then instructing the DHCP provider (for example, the Networking service) to boot the node from it. See Example 1: PXE Boot and iSCSI Deploy Process and Example 2: PXE Boot and Direct Deploy Process for a better understanding of the whole deployment process.


Both PXE and iPXE are configured differently, when UEFI boot is used instead of conventional BIOS boot. This is particularly important for CPU architectures that do not have BIOS support at all.

The pxe boot interface is used by default for many hardware types, including ipmi, and for all classic drivers with names starting with pxe_. Some hardware types, notably ilo and irmc have their specific implementations of the PXE boot interface.

Additional configuration is required for this boot interface - see Configuring PXE and iPXE for details.

Enable persistent boot device for deploy/clean operation

Ironic uses non-persistent boot for cleaning/deploying phases as default, in PXE interface. For some drivers, a persistent change is far more costly than a non-persistent one, so this can bring performance improvements.

Set the flag force_persistent_boot_device to True in the node’s driver_info:

$ openstack baremetal node set --driver-info force_persistent_boot_device=True <node>


It’s recommended to check if the node’s state has not changed as there is no way of locking the node between these commands.

Once the flag is present, the next cleaning and deploy steps will be done with persistent boot for that node.

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