[Pacemaker] Corosync over DHCP IP

[Dennis Jacobfeuerborn]

On 02/12/2013 03:15 AM, Andrew Beekhof wrote:
> On Tue, Feb 12, 2013 at 1:01 PM, Dennis Jacobfeuerborn
> <dennisml at conversis.de> wrote:
>> On 02/12/2013 02:38 AM, Andrew Beekhof wrote:
>>> On Tue, Feb 12, 2013 at 3:09 AM, Dennis Jacobfeuerborn
>>> <dennisml at conversis.de> wrote:
>>>> On 02/11/2013 11:30 AM, Andrew Beekhof wrote:
>>>>> On Mon, Feb 11, 2013 at 9:24 PM, Viacheslav Biriukov
>>>>> <v.v.biriukov at gmail.com> wrote:
>>>>>> It is VM in the OpenStack. So we can't use static IP.
>>>>>> Right now investigating why interface become down.
>>>>>
>>>>> Even if you solve that, dynamic IP addresses are fundamentally
>>>>> incompatible with cluster software.
>>>>> You're effectively trying to create a cluster out of nodes which
>>>>> change their name every time they boot.
>>>>
>>>> DHCP doesn't necessarily mean a dynamic IP.
>>>
>>> In most (if not all) openstack deployments, it does.
>>> Even better, the static IPs you can assign belong to the physical
>>> hosts and don't show up inside the guests - so corosync can't bind to
>>> them.
>>
>> You are probably talking about the floating IPs. The primary IPs (usually
>> in the 10.0.0.0/8 range) of the interfaces however should work fine for
>> this. There's no magic involved.
> 
> If they don't show up in 'ip addr', which they don't in openstack
> guests, then corosync can't use them.
> There is no way to say "Your address is w.x.y.z but you'll get
> messages on a.b.c.d".

They show up like like any other interface in 'ip addr'. There is no magic
involved in any of this.
The machine gets assigned a primary IP from the assigned network which is
stored in the dhcp leases database and usually (but not necessarily) it
gets assigned a floating ip that is reachable from the internet which is
NATed to the primary IP.
When the guest boots it discovers its primary IP via dhcp and assignes that
IP to eth0.
There is no reason why corosync shouldn't be able to use that IP to address
the cluster nodes.

Regards,
  Dennis