extra dhcp options not exposed to pxe deploy ramdisk

[Adam Gandelman]

I'm attempting to deploy in an environment where I need to push out MTU settings to nodes via DHCP, but this is currently not possible. There is a documented solution for this on the Neutron side @ http://docs.openstack.org/admin-guide-cloud/content/openvswitch_plugin.html

Ironic's current pxe_config.template contains the "ipappend 3" kernel parameter for the deploy ramdisk. This causes pxelinux to append (among other things) ip=$ip:$boot_server:$gw:$netmask to the kernel parameters. The deploy-ironic ramdisk will use these settings to manually bring up networking rather than relying on DHCP. If no networking is passed via kernel params, it will instead use DHCP and any additional options, ie forced MTU, will be honored.** syslinux docs suggest, wrt 'ipappend 3':

Note: The use of option 1 is no substitute for running a DHCP client in the booted system and should instead only be used to seed the client for a request. Without regular renewals, the lease acquired by the PXE BIOS will expire, making the IP address available for reuse by the DHCP server.

IMO the pxe template should change to 'ipappend 2', which will cause pxelinux to not pass minimal networking info via kernel params, and allow the ramdisk to request DHCP from Neutron, where operators have the ability to push additional tweaks to clients. There may be some DIB work that needs to be done here, as well.

** There is a current diskimage-builder bug around the DHCP code path in its ramdisk, but it is expected to work: https://bugs.launchpad.net/diskimage-builder/+bug/1401289

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/141148

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/141148
Committed: https://git.openstack.org/cgit/openstack/ironic/commit/?id=cb82dabdca5c37d9ac54e4c207a896a32f18525b
Submitter: Jenkins
Branch: master

commit cb82dabdca5c37d9ac54e4c207a896a32f18525b
Author: Adam Gandelman <email address hidden>
Date: Thu Dec 11 11:31:19 2014 -0800

    Do not pass PXE net config from bootloader to ramdisk

    All PXE templates currently pass network configuration from the
    bootloader to the ramdisk via a kernel parameter,
    ip=$ip:$tftp-server:$gateway:$netmask. The current deploy-ironic
    ramdisks built by DIB uses this to bring up networking manually,
    but this behavior exists there for non-PXE deployments where DHCP
    is unavailable. We ideally want ramdisks to use DHCP to allow pushing
    more than just ip/gw/nm. This updates PXE templates to not pass net config,
    since DHCP is assumed to be functioning for all PXE env. Without the
    ip= parameter, the ramdisk has no easy way to resolve the boot server's
    address. To signal where to callback to, a boot_server parameter has
    been added that points back to the TFTP server address.

    Closes-bug: 1401298

    Change-Id: Icc04de7b8b7324ce685f930d2e8074b0c764fc0c

[Jim Rollenhagen (jim-rollenhagen)]

Re-opened, we had to revert this because it broke tripleo Fedora jobs: https://review.openstack.org/#/c/152129/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/152551

[OpenStack Infra (hudson-openstack)]

Change abandoned by Adam Gandelman (<email address hidden>) on branch: master
Review: https://review.openstack.org/152551

[John L. Villalovos (happycamp)]

Etherpad discussion:

https://etherpad.openstack.org/p/ironic-multi-node

[Michael Turek (mjturek)]

This wishlist bug has been open more than a year without any activity. I'm going to move it to "Opinion / Wishlist", which is an easily-obtainable queue of older requests that have come on. This bug can be reopened (set back to "New") if someone decides to work on this.