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On 3 February 2015 at 00:48, Kevin Benton <blak111 at gmail.com> wrote:
>>The only thing this discussion has convinced me of is that allowing users
>> to change the fixed IP address on a neutron port leads to a bad
>> user-experience.
...

>>Documenting a VM reboot is necessary, or even deprecating this (you won't
>> like that) are sounding better to me by the minute.
>
> If this is an approach you really want to go with, then we should at least
> be consistent and deprecate the extra dhcp options extension (or at least
> the ability to update ports' dhcp options). Updating subnet attributes like
> gateway_ip, dns_nameserves, and host_routes should be thrown out as well.
> All of these things depend on the DHCP server to deliver updated information
> and are hindered by renewal times. Why discriminate against IP updates on a
> port? A failure to receive many of those other types of changes could result
> in just as severe of a connection disruption.

So the reason we added the extra dhcp options extension was to support
PXE booting physical machines for Nova baremetal, and then Ironic. It
wasn't added for end users to use on the port, but as a generic way of
supporting the specific PXE options needed - and that was done that
way after discussing w/Neutron devs.

We update ports for two reasons. Primarily, Ironic is HA and will move
the TFTPd that boots are happening from if an Ironic node has failed.
Secondly, because a non uncommon operation on physical machines is to
replace broken NICs, and forcing a redeploy seemed unreasonable. The
former case doesn't affect running nodes since its only consulted on
reboot. The second case is by definition only possible when the NIC in
question is offline (whether hotplug hardware or not).

-Rob


-- 
Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Converged Cloud