Open Stack

It depends on your network setup.  In our environment, for example, the
metadata host(s) are set up to actively ARP for 169.254.169.254.  This
means the guests must have the route for 169.254/16, so it will ARP
who-has for the metadata IP.

But if your upstream router is configured to know about the metadata IP
and where requests for it need to go, then the guests do not need the
route.  They just send requests to the default gateway, and it sorts it
out.  (I am not really up on the different nova-network and neutron
setups, but I think this is the situation that applies when the guests¹
default gateway is a ³network node², which handles NATting or proxying
metadata requests to the right place.)

On EL distros, you can remove NOZEROCONF=yes from the ifcfg-eth0 config
file, and that _should_ set up the 169.254 route for you (I think.)  Or
you can set the route explicitly in the route-eth0 conf file.  I assume
there is similar config for Ubuntu, etc.

I have thought that being able to pass down static routes like this via
DHCP would be useful, too.  But I am not familiar enough with the Neutron
architecture to understand the feasibility of that, and we¹ve been able to
work around this more easily by baking the metadata route into images.

Mike



On 5/23/14, 5:21 AM, "Adrian Smith" <adrian.smith at workday.com> wrote:

>Should VMs always have a static route to the 169.254 subnet so they
>can access the metadata service?
>
>In my VMs attempting the following request works with a route but just
>times out without it,
>
>$ curl http://169.254.169.254/latest/meta-data/instance-id
>
>Works with these routes,
>
>Destination     Gateway         Genmask         Flags Metric Ref    Use
>Iface
>10.52.10.0      0.0.0.0         255.255.255.0   U     0      0        0
>eth0
>169.254.0.0     0.0.0.0         255.255.0.0     U     0      0        0
>eth0
>0.0.0.0         10.52.10.1      0.0.0.0         UG    0      0        0
>eth0
>
>But doesn't work these,
>
>Destination     Gateway         Genmask         Flags Metric Ref    Use
>Iface
>10.52.10.0      0.0.0.0         255.255.255.0   U     0      0        0
>eth0
>0.0.0.0         10.52.10.1      0.0.0.0         UG    0      0        0
>eth0
>
>If we need the route then dhclient should request 121, "Classless
>Static Route" right? My VM isn't including this in it's DHCP request
>but I guess that's just something I need to configure in dhclient.
>However I don't want to do this if the route is unnecessary to start
>with (and just points to something else is wrong in my setup).
>
>Adrian
>
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