Sometimes the instance takes a long time to boot up, anywhere from a few seconds to 5 minutes. This is due to a timer where by the instance is waiting for the network interface to come up. This is an log extract:
[0m] A start job is running for Raise network interfaces (6s / 5min 1s)[K[[0;1;31m*[0m[0;31m* [0m] A start job is running for Raise network interfaces (7s / 5min 1s)[K[[0;32m OK [0m] Started Raise network interfaces.
In this secenario the server can be waiting up to 5 minutes for the interface to be found or it will keep trying until it reaches the 5 minute period. The alternative to this is to set a lower time out, technically the 5 minutes is already a timeout otherwise it will continue waiting until forever.
The file is found at: /etc/dhcp/dhclient.conf on the very last line, it has timeout 300; this is measured in the number of seconds. We can lower this to a smaller value for the timeout.