[openstack-dev] [Neutron][dns]What the meaning of "dns_assignment" and "dns_name"?

Miguel Lavalle miguel at mlavalle.com
Wed Oct 14 03:22:24 UTC 2015

Zhi Chang,

Thank you for your questions. We are in the process of integrating Neutron
and Nova with an external DNS service, using Designate as the reference
implementation. This integration is being achieved in 3 steps. What you are
seeing is the result of only the first one. These steps are:

1) Internal DNS integration in Neutron, which merged recently:
https://review.openstack.org/#/c/200952/. As you may know, Neutron has an
internal DHCP / DNS service based on dnsmasq for each virtual network that
you create. Previously, whenever you created a port on a given network,
your port would get a default host name in dnsmasq of the form
'host-xx-xx-xx-xx.openstacklocal.", where xx-xx-xx-xx came from the port's
fixed ip address "xx.xx.xx.xx" and "openstacklocal" is the default domain
used by Neutron. This name was generated by the dhcp agent. In the above
mentioned patchset, we are moving the generation of these dns names to the
Neutron server, with the intent of allowing the user to specify it. In
order to do that, you need to enable it by defining in neutron.conf the
'dns_domain' parameter with a value different to the default
'openstacklocal'. Once you do that, you can create or update a port and
assign a value to its 'dns_name' attribute. Why is this useful? Please read

2) External DNS integration in Neutron. The patchset is being worked now:
https://review.openstack.org/#/c/212213/. The functionality implemented
here allows Neutron to publish the dns_name associated with a floating ip
under a domain in an external dns service. We are using Designate as the
reference implementation, but the idea is that in the future other DNS
services can be integrated.. Where does the dns name and domain of the
floating ip come from? It can come from 2 sources. Source number 1 is the
floating ip itself, because in this patchset we are adding a dns_name and a
dns_domain attributes to it. If the floating ip doesn't have a dns name and
domain associated with it, then they can come from source number 2: the
port that the floating ip is associated with (as explained in point 1,
ports now can have a dns_name attribute) and the port's network, since this
patchset adds dns_domain to networks.

3) Integration of Nova with Neutron's DNS. I have started the
implementation of this and over the next few days will push the code to
Gerrit for first review. When an instance is created, nova will request to
Neutron the creation of the corresponding port specifying the instance's
hostname in the port's 'dns_name' attribute (as explained in point 1). If
the network where that port lives has a dns_domain associated with it (as
explained in point 2) and you assign a floating ip to the port, your
instance's hostname will be published in the external dns service.

To make it clearer, here I walk you through an example that I executed in
my devstack: http://paste.openstack.org/show/476210/

As mentioned above, we also allow the dns_name and dns_domain to be
published in the external dns to be defined at the floating ip level. The
reason for this is that we envision a use case where the name and ip
address made public in the dns service are stable, regardless of the nova
instance associated with the floating ip.

If you are attending the upcoming Tokyo summit, you could attend the
following talk for further information:
Looking forward to see you there!

Hope this answers your questions

Best regards

Miguel Lavalle

On Tue, Oct 13, 2015 at 9:58 AM, Zhi Chang <changzhi at unitedstack.com> wrote:

> Hi, all
>     I install the latest devstack and create a vm by nova. I get the
> port's info which created by Neutron. I'm confused that what the meaning of
> column "dns_assignment" and column "dns_name".
>     First, column "dns_assignment" is a read-only attribute. What is it
> used for? I think that this column is useless except shows DNS infomation
> (include hostname, ip, fqdn). Does my thought right?
>     Second, I don't quite understand what the meaning of column
> "dns_name". I can update this column, but there is nothing happen when my operation
> was done. In other words, this column has no change when I run "neutron
> port-update xxx --dns_name=test". What the column "dns_name" use for?
> Thanks
> Zhi Chang
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