According to the docs (http://docs.pylonsproject.org/projects/waitress/en/latest/):
Waitress sends its logging output (including application exception renderings) to the Python logger object named waitress. You can influence the logger level and output stream using the normal Python logging module API.
That's all the documentation has to say. I'm trying to redirect logging output to stdout. How would I go about doing that in the pastedeploy .ini file?
So, the problem appears to be that the official heroku migration documentation (http://docs.pylonsproject.org/projects/pyramid_cookbook/en/latest/deployment/heroku.html) fails to tell you that you need to initialize the logger for waitress before the app is initialized. Otherwise, nothing gets logged.
So, my question was incorrect. It's not that logging was going to stderr, it was that logging was going nowhere.
The solution is to make the following changes to your runapp.py file.
Are you trying to log the requests to waitress? I could never get it working also. If fact I asked the question on SO a couple of years ago and someone said it couldn't be done.
For a work around I added a pyramid "subscriber" that does all the logging for each request.
Edit.
On reviewing my code I stopped using a subscriber and switched to using a tween for logging. Both ways will work.
tweens.py
Add this to your Pyramid Configuration