How strong of an obligation does an advisor have to attend his/her Ph.D. students' graduation? I will be graduating my first Ph.D. student this summer. My student is quite strong and has done good work, and I am quite proud of him!

I do face one conundrum. He has expressed the hope that I would be there for his Ph.D. hooding and graduation ceremony. It seems like an utterly natural, totally reasonable thing to ask for. I was tenatively planning on being out of the country at the time, so I need to decide whether to cancel my plans to attend his graduation.

On the one hand, missing my student's graduation seems like the equivalent of missing your best friend's wedding. Or perhaps worse, missing your child's wedding, or your own. On the other, this seems to be very common. My own Ph.D. advisor was out of town for my graduation and I asked another professor on my committee to escort me in his place.

Is there any kind of consensus?
Obligation? Unless through your institution's academic responsibilities there is a requirement to attend, then none.

However, if you equate it to being on par with missing your own child's wedding, then I think you've answered your own question. 

You only get one 'first Ph.D. student'.