Comment 9 for bug 1353008

cloud-init doesn't "fail fast". Rather, the 'cloud-init' upstart job will not execute until either:
a.) all network interfaces defined in /etc/network/interfaces as 'auto' are up
or
b.) cloud-init-nonet has ended (which basically blocks boot for up to 120 seconds or until 'a' is accomplished).

one of the two scenarios must be reached before the 'mounted MOUNTPOINT=/' event occurs. That event then basically blocks the rest of boot. so cloud init forces a pinch point in boot on networking coming up.

something else must be blocking networking from coming up until afer mounted MOUNTPOINT=/ has occurred.

Possibly a dupe of https://bugs.launchpad.net/cloud-init/+bug/1345433