These two words have related but different meanings—and grammar.
Raucous is an adjective meaning “loud, active, and out of control”—like a group of children playing or a college party.
Ruckus has essentially the same meaning as raucous, but is a noun—it refers to a disturbance or commotion:
The college party was so raucous that the neighbors called the police.
The children were making a ruckus, so we sent them to play outside.
Note: These words describe only non-harmful behavior, such as play; they do not describe violence or war.