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Customize OpenStack images for booting from ISCSI

When working with OpenStack Ironic and Tripleo, and using the boot from ISCSI feature, you may need to add some kernel parameters into the deployment image for that to work.
When using some specific hardware, you may need that the deployment image contains some specific kernel parameters on boot. For example, when trying to boot from ISCSI with IBFT nics, you need to add following kernel parameters:

rd.iscsi.ibft=1 rd.iscsi.firmware=1 

 The TripleO image that is generated by default doesn't contain those parameters, because they are very specific depending on the hardware you need. It is not also possible right now to send this parameters through Ironic.

The solution will be to customize the deployment image to add these kernel parameters. The overcloud-full.qcow2 image that comes by default with TripleO is a partition image. It means that the bootloader is not previously installed, but it is done through Ironic. So the way to add custom parameters, is modifying the /etc/default/grub file, adding those parameters.

So let's do it step by step:

1. On the undercloud, install libguestfs-tools: sudo yum install -y libguestfs-tools
2. On /home/stack, you will find overcloud-full.qcow2 image. Start customizing it:

export LIBGUESTFS_BACKEND=direct
guestfish -a overcloud-full.qcow2
<fs> run

<fs> list-filesystems
<fs> mount /dev/sda /
<fs> vi /etc/default/grub

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8 crashkernel=auto rhgb quiet"
GRUB_DISABLE_RECOVERY="true"

Edit GRUB_CMDLINE_LINUX and append the kernel parameters you need there. Exit the editor saving the file, and exit from guestfish

<fs> exit

Now is time to upload the modified image:

source /home/stack/stackrc
openstack overcloud image upload --existing

Now redeploy again, and the image will boot with the modified kernel parameters, allowing boot from ISCSI to work with your hardware.

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