expecting metadata server is reachable on the lexical first interface

[Robert Schweikert]

In OpenStack it is possible to configure a network setup such that the metadata server is accessible via a "secondary" NIC, for example eth1. In such a setup cloud-init fails to locate the proper NIC to access the metadata server.

[Robert Schweikert (rjschwei)]

When after discovering all available interfaces in find_fallback_nic() the nics are sorted in lexical order and then the first nic that has an address, i.e. /sys/class/net/$NIC_NAME/address has useful data is assumed to be the NIC to use for accessing the metadata server. However, this may not be true.

What's missing is a fall back loop that attemps to access the metadata server over other possible network interfaces.

[Edward Hope-Morley (hopem)]

Access to the metadata network is decided by a default route for 169.254.169.254/32 from Openstack installed via dhcp. From what I can tell if you have more than one port attached to a vm and only one of those ports is attached to a network providing dhcp then you have to ensure that port is the first one attached to the instance so it gets dhcp and the default route. Then further ports attached and configured will not stop metadata from being reached.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3322