On Mon, Mar 23, 2020 at 3:37 PM Brian Haley <haleyb.dev@xxxxxxxxx
<mailto:haleyb.dev@xxxxxxxxx>> wrote:
On 3/23/20 10:48 AM, Ryan Harper wrote:
>
> On Mon, Mar 16, 2020 at 8:44 AM Slawek Kaplonski
<skaplons@xxxxxxxxxx <mailto:skaplons@xxxxxxxxxx>
> <mailto:skaplons@xxxxxxxxxx <mailto:skaplons@xxxxxxxxxx>>> wrote:
>
> Hi,
>
> > On 11 Mar 2020, at 20:13, Ryan Harper
<ryan.harper@xxxxxxxxxxxxx <mailto:ryan.harper@xxxxxxxxxxxxx>
> <mailto:ryan.harper@xxxxxxxxxxxxx
<mailto:ryan.harper@xxxxxxxxxxxxx>>> wrote:
> >
> >
> >
> > On Wed, Mar 11, 2020 at 4:39 AM Slawek Kaplonski
> <skaplons@xxxxxxxxxx <mailto:skaplons@xxxxxxxxxx>
<mailto:skaplons@xxxxxxxxxx <mailto:skaplons@xxxxxxxxxx>>> wrote:
> > Hi,
> >
> > Hi Slawek,
> >
> > Thanks for reaching out to the cloud-init community.
> >
> >
> > I’m OpenStack Neutron developer. Since some time we have
proposed
> spec [1] about Metadata over IPv6 in IPv6 only networks.
> > This spec proposes to use fe80::a9fe:a9fe IP address as it is
> equivalent of 169.254.169.254 in IPv6 link-local subnet.
> >
> > According to [2] I know already that cloud-init can be
configured
> to use any metadata urls with “metadata_urls” so we can use such
> IPv6 address (or any other) and can be configured to be used in
> cloud-init on guest vms.
> > But as cloud-init is one of the biggest users of Metadata
> service, I would like to ask cloud-init community what do You
think
> about it and if this will work for You.
> > Any feedback here or in the spec's review will be
appreciated :)
> >
> > Some initial thoughts and questions:
> >
> > - In what order should cloud-init try ipv6 and ipv4?
> > - cloud-init would prefer to know which one it should
use so
> we don't timeout on an endpoint that isn't there.
>
> I would say that it it could be checked what IP addresses are
> configured in the guest OS already and use correct one if
only one
> type of addresses is there. If there would be both IPv4 and
IPv6, it
> could try IPv4 first as it is like that now. What do You
think about
> such solution?
>
>
> cloud-init runs before networking comes up. In OpenStack,
cloud-init
> will to an Ephemeral DHCP to try to reach metadata service over
IPV4.
> Once metadata service is crawled, cloud-init will write out network
> configuration obtained from metadata service.
> Currently we will try a list of URLs/IPs as configured in the
> datasource. We can add the IPv6 metadata url to the list, my
question
> is where in the list should it go? If we put it first, then on
> deployments which lack IPv6 metadata service, all VMs will pay a
> boot speed cost of trying to fetch metadata from a non-existent
URL. If
> the v6 address is at the end, then IPv6-only deployments will
waste time
> trying to hit an IPv4 url which is not present. This is why I'm
> interested in being "told" in some way.
> This knowledge would need to come from a non-network area.
Typically
> this is done via DMI tables; however, DMI is not a complete
solution as
> this is not available on all architectures (s390x and ppc64le and
some
> arm64), which makes this
> sub-optimal.
I think in our Openstack case, there are three possibilities. Assuming
DHCP succeeds and assigns an IP to the interface, metadata should use
the following address based on what is configured:
- IPv4-only: IPv4 metadata address
- IPv6-only: IPv6 metadata address
- dual-stack: either should work, prefer IPv4
I get your idea, let's reword this a bit to confirm since we'll always
have ipv6 link-local
on our nic; the only variable is whether DHCPv4 will respond with an IP.
- DHCP response with v4 address -> prefer v4 metadata address
- NoDHCP response -> try IPv6 metadata url
> > -
> > - cloud-init's EphemeralDHCP code currently relies upon
dhclient
> and ipv4 ips/routes; this will need updating to work with v6;
what
> is needed use fe80::a9fe:a9fe ?
>
> As this is link local IP address it should be reachable
without any
> configuration if IPv6 is enabled on the interface in the guest.
>
>
> OK. That makes the v6 support simpler.
>
>
> > - is there a chance that Metadata is available over either
v4 or v6?
> > - would the data ever diverge?
>
> I don’t know if this data can diverge in the future.
>
>
> Reading the spec, it appeared to me that the metadata service has no
> changes, rather this was more about configuring which network ports
> expose the service.
> I would not expect there to be a different metadata service on v4
from
> v6 (the instance-id is the same either path);
>
>
> >
> >
> > Thanks,
> > Ryan Harper
> >
>
> —
> Slawek Kaplonski
> Senior software engineer
> Red Hat
>
