When you say whiteboard do you mean for drawing or just communication? Here's a free open source ready to deploy chat + audio + video solution https://rocket.chat/ but it lacks drawing.
For whiteboard drawing, https://webwhiteboard.com uses a canvas tag.
I have also been on a team which created our own whiteboard for internal use purely with node / sockets / webrtc. It's not great and it took months but it's doable.