  The Network Function Virtualization (NFV) paradigm is enabling flexibility,
programmability and implementation of traditional network functions into
generic hardware, in form of Virtual Network Functions (VNFs). To provide
services, the VNFs are commonly concatenated in a certain ordered sequence,
known as Service Function Chains (SFCs). SFCs are usually required to meeting a
certain level of reliability. This creates the need to place the VNFs while
optimizing reliability jointly with other objectives, such as network and
server load balancing. Traditional migration and replication mechanisms,
commonly used for Virtual Machines (VM) in data centers, can be used to improve
SFC reliability. We study how to improve service reliability using jointly
replications and migrations, considering the chaining problem inherent in NFV.
While replications provide reliability, performing migrations to more reliable
servers decreases the resource overhead. A Linear Programming (LP) model is
presented to study the impact of active-active configurations on the network
and server resources. Additionally, to provide a fast recovery from server
failures, we consider N-to-N configurations in NFV networks and study its
impact on server resources. The results show that replications do not only
improve reliability, but can also be used to achieving a better server and
network load balancing, and when used jointly with migrations can improve
resource utilization without degrading reliability.
