While using Dokku, I was getting the following error message: Requested runtime (python-2.7.8) is not available for this stack (cedar-14).
This was due to a connection error between my docker container and the internet. To determine this, I ran "docker images" and got the image id of "programium/buildstep", then got into a container with the following command: sudo docker run -t -i <your image id> /bin/bash
Once in the container, I ran:
curl http://lang-python.s3.amazonaws.com/cedar/runtimes/python-2.7.8.tar.gz -s
If that is unsuccessful, that should confirm it's a connection issue.
This was the solution to the problem: http://www.paulsprogrammingnotes.com/2014/12/rebuilding-buildstep-image-for-dokku.html