o be redefined or renormalized. Once the appropriate NFV-based resiliency requirements are defined, the measurement and monitoring architecture must change to accommodate the new cloud-based delivery platform. The design challenge for NFV is to create a five-nines carrier grade application using commer- cial cloud technology that is designed to operate in the 3-9s (99.9%) availability range (Amazon Web Services, 2013; Hoff, 2015; Butler, 2016; Taylor, 2016). In this chapter, a comprehensive, mul- tilayer view demonstrating how carrier grade availability can be achieved in this environment is developed. Both the Network Cloud infrastructure as well as the application architecture of the virtual functions (VFs) are considered. As shown in Figure 5.1, the Network Cloud infrastructure includes the physical infrastructure (servers, network, storage, and physical plant) and the virtu- alization infrastructure (hypervisor and virtual machine [VM]). Availability tradeoffs among the different infrastructure components are addressed, as are the impacts of planned downtime and georedundancy. Next, the critical attributes of high availability VF designs are defined. Achieving Cloud Site Application VNF Automation Layer (e.g. ONAP) Cloud Stack (e.g. Openstack) Virtual Machine (VM) Hypervisor Network Server Storage Fabric Physical Plant FIGURE 5.1 Layers of a network cloud. Architecting the Network Cloud for High Availability 5-9s carrier grade availability requires that VF designers use resilient design patterns that include spatial redundancy with redundant hardware, redundant information with redundant data structures, and temporal redundancy with redundant computation. Finally, the principles of high availability designs are demonstrated for different types of VFs, showing how high availability can be achieved. For the purposes of this discussion, it is important to distinguish between availability, reliability, and resiliency. Availability is defined as the time-based probability that the "entity" is operational, where th