It took reading through this launchpad bug to find ideas on how to get a bonding interface working on Ubuntu. This is dumb and why people hate computers: could they at least have provided a more useful syntax or better warning messages?

auto eth7
allow-bond0 eth7
iface eth7 inet manual
   bond-master    bond0
   mtu            9000

auto eth8
allow-bond0 eth8
iface eth8 inet manual
   bond-master    bond0
   mtu            9000

auto bond0
iface bond0 inet static
   address        10.52.0.1
   netmask        255.255.255.0
   network        10.52.0.0
   gateway        10.52.0.2
   bond-slaves    eth7 eth8
   bond-mode      balance-rr
   bond-miimon    100
   bond-downdelay 200
   bond-updelay   200
   mtu            9000
   use-carrier    1
   pre-up (sleep 2 && ifup eth7) &
   pre-up (sleep 2 && ifup eth8) &

And you want to make sure all interfaces are down. Then rmmod bonding. At this point, ifup bond0 should complain a bit but it should work.