Network functions virtualization (NFV) can reduce infrastructure costs and increase business agility, but assuring service levels and performing root-cause analysis when issues occur becomes far more complex with its introduction. Since most NFV projects occur in stages over long periods of time, many organizations run NFV infrastructure alongside legacy hardware simultaneously. Providing service assurance in these mixed environments introduces new challenges. While significant time and effort have been spent on NFV orchestration, automating NFV service assurance alongside legacy infrastructure is as important, or even more important, for resolving issues rapidly and preventing outages.