It looks like there is an issue with six with havana nova (milestone-proposed). Nova has: six<1.4.0 python-keystoneclient>=0.3.2 Latest keystoneclient (0.4.1) has: six>=1.4.1 Does nova need to require an older version of keystoneclient? Downgrading to 0.3.2 will fix it. Cheers, Sam