I've been reading up on the Lightning Network, and I read that you can earn routing fees by having users relay LN transactions through your node. What I'd like to know is this:

• How can I determine if someone decided to relay through my node? Through incoming connections?
• Are open channels imperative to earning routing fees? If so, how many are optimal?

I'm aware that I might earn only a handful of satoshi, but I'm interested in new experiences and technologies.