[Openstack-operators] Two regions and so two metadata servers sharing the same VLAN

Gilles Mocellin gilles.mocellin at nuagelibre.org
Thu Dec 3 23:56:10 UTC 2015

Hum, I don't think so. Things like hostname must be only known by the 
neutron instance of one region...

Le 03/12/2015 00:01, Kevin Benton a écrit :
> Are both metadata servers able to provide metadata for all instances 
> of both sides? If so, why not disable isolated metadata on one of the 
> sides so only one of the DHCP agents will respond?
> On Thu, Nov 26, 2015 at 6:49 AM, <gilles.mocellin at nuagelibre.org 
> <mailto:gilles.mocellin at nuagelibre.org>> wrote:
>     Hello stackers !
>     Sorry, I also cross-posted that question here
>     https://ask.openstack.org/en/question/85195/two-regions-and-so-two-metadata-servers-sharing-the-same-vlan/
>     But I think I can reach a wider audience here.
>     So here's my problem.
>     I'm facing an non-conventional situation. We're building a two
>     region Cloud to separate a VMware backend and a KVM one. But both
>     regions share the same 2 VLANs where we connect all our instances.
>     We don't use routers, private network, floating IPs... I've
>     enabled enable_isolated_metadata, so the metadata IP is inside the
>     dhcp namespace and there's a static route in the created instances
>     to it via the dhcp's IP. The two DHCPs could have been a problem
>     but we will use separate IP ranges, and as Neutron sets static
>     leases with the instances MAC address, they should not interfere.
>     The question I've been asked is whether we will have network
>     problems with the metadata server IP, that will
>     exist in 2 namepaces on 2 neutron nodes but on the same VLAN. So
>     they will send ARP packets with different MAC, and will perhaps
>     perturb access to the metadata URL form the instances.
>     Tcpdump shows nothing wrong, but I can't really test now because
>     we haven't got yet the two regions. What do you think ?
>     Of course, the question is not about why we choose to have two
>     regions. I would have chosen Host Agregates to separate VMware and
>     KVM, but cinder glance should have been configure the same way.
>     And with VMware, it's not so feasible.
>     Also, if we can, we will try to have separate networks for each
>     regions, but it involves a lot of bureaucracy here...
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> -- 
> Kevin Benton

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