Lori MacVittie dives into the difficulty of enabling SDN/OpenFlow controllers. It’s really worth a read!
In other words, the gut instincts of network operators is right: code controlling core routing and switching – which will be necessarily high in cyclomatic complexity by nature of what it has to do to perform tasks – is almost certain to be prone to higher error rates. Such reality butts heads against the definition of “reliable”, making the two not very complementary.