How to identify a heroku dyno number from within the app?

Is there a way to identify the heroku dyno name (e.g. web.1, web.2) from within the application? I'd like to be able to generate a unique request id (e.g. to track requests between web and worker dynos for consolidated logging of the entire request stack) and it seems to me that the dyno identifier would make a decent starting point.

If this can't be done, does anyone have a fallback recommendation?