Comment by walterbell

Application virtualization is not easy. Docker has done an amazing job of marketing the benefits, but the long-term solution is that OS and application developers (not sysadmins) will design minimal OS+app bundles. See recent discussion on Microsoft research, https://news.ycombinator.com/item?id=8257250

Docker+CoreOS mimics Google infrastructure - CoreOS is probably a better "minimal server OS" choice for Docker than Ubuntu.