  Traditionally, Network Function Virtualization (NFV) has been implemented to
run on Virtual Machines (VMs) in form of Virtual Network Functions (VNFs). More
recently, the so-called Serverless Computing has gained traction in cloud
computing, offering Function-as-a-Service (FaaS) platforms that make use of
containerization techniques to deploy services. In contrast to VM-based VNFs,
where resources are usually reserved and continuously running, FaaS can just be
subsets of code implementing small functions allowing for event-driven,
on-demand instantiations. Thus, a hybrid VM-Container based Service Function
Chains (SFCs) are a natural evolution of NFV architecture. We study a novel
problem of optimal placement of hybrid SFCs from an Internet Service Provider
(ISP) point of view, whereby VNFs can be instantiated either over VMs or
containers in a generic edge and cloud continuum. To this end, we propose a
Mixed-Integer Linear Programming model as well as a heuristic solution to solve
this optimization problem that considers three objectives unique to the
specific VM and container deployment in a carrier network: operational costs
for maintaining servers in the edge, costs of placing VNFs in third-party cloud
providers and penalty costs applied when SLA agreements are violated in terms
of end-to-end delay. We also propose 2-phases optimization process to analyze
the effect on performance as a result of replications and migrations of VNFs.
The model can be used to highlight scenarios where a combination of VMs and
containers can provide most benefits from the monetary costs point of view.
