He does have a point although he might not have meant to. I've setup both Cloud.com's stack and the OpenStack for smallish private clouds and I have to agree with him. Java was a poor choice for the project and my experience of it (6-7 months ago, caveat emptor) was that it was riddled with bugs and suffered from more than a few bad design decisions. It's 200k+ lines, with very few tests (I'd wager on single digit coverage if I was a betting man), has a homemade ORM (why no hibernate?), the design of the instance image delivery system defies all human logic and there's no proper messaging queue anywhere to be found. Add to that colourful spectrum of inconsistencies and you end up with a lot of issues. However, I'm not saying that those issues are Java's fault, they clearly aren't. But, with any language choice there comes a culture and I don't think I'm being unfair when I say that I see these kinds of things more in Java projects than in Python. For comparison, the OpenStack is about ~70k lines (~30k of which are tests).