Preposition use: ON or AT the Dragon Boat Festival?
Solution 1:
The use of the term "festival" leads one to think of an event held at a particular location; it follows that one would use "at" as the appropriate preposition. If one were to characterize the event as a "holiday" the implication would be that it is a widely celebrated event that is not limited to a particular location; in this circumstance, "on" would be the appropriate preposition. So I think the deciding factor would be how the event is characterized.