## 6 Conclusions  
This paper shows a lightweight architecture for implementing network services through NFV. It exploits the flexibility of the serverless approach to deploy evolved IoT applications, such as IoV, smart manufacturing, smart health and smart grid applications.  
This proposed architecture includes innovative technologies, such as NetBricks, which is an NFV framework focused on a safe runtime and optimized function modules. It also includes Kata Containers, a lightweight container runtime which makes use of a microVM to wrap applications and improve isolation, which can be boosted by Firecracker. The latter is a VMM based on KVM, with fast startup times and a low memory footprint. The combination of low resource usage and robust isolation also makes this architecture suitable for edge/MEC-based service platforms, which are typically used for implementing IoT applications. Security is also improved due to the reduction in the attack surface of microVMs instantiated by Firecracker.  
The experimental results show that the proposed architecture exhibits a significant reduction in both resource footprint, in comparison with legacy approaches, and VNF instantiation time, which may be a critical parameter for serverless computing. Data plane performance fully satisfies the performance requirements of most IoT applications, and are aligned with those based on the classic QEMU hypervisor. However, a trade-off between latency and resource footprint, along with the introduction of extra layers of isolation, exists. This trade-off makes the proposed system unsuitable for some very demanding uRLLC applications, and this is actually still an open area of research.  
In our system, we used both NetBricks and standard packages, both encapsulated in Kata containers, running in Firecrackers microVMs. Although NetBricks cannot be a suitable choice for all applications, thanks to its efficiency in packet processing, which is accelerated by the usage of DPDK, it can be an excellent solution for implementing low level functions needing fast packet processing, such as VPN gateways. However, in complex services made of several functions, such as vehicular or video streaming services, some high-level functions can be implemented using already available packages, running in Kata containers and hosted in Firecracker microVMs. We have shown that, even in this case, our proposal provides significant advantages over the baseline solutions.  
The proposed solution is not an alternative to using AI techniques to anticipate the instantiation of VNFs in a serverless framework, but rather is complementary to them, since it is able to minimize the impact of an incorrect decision.  
Future works will consider a larger experimental campaign, using Kubernetes to perform resource management and orchestration. This would also include mobility services, to evaluate with real tests the time advance needed to generate a VNF on a different edge node to guarantee service continuity, depending on the service requirements.  
Conceptualization, G.R.; methodology, G.R.; validation, M.F.; writing--original draft preparation, M.F.; writing--review and editing, G.R.; funding acquisition, M.F. and G.R. All authors have read and agreed to the published version of the manuscript.  
This work has been supported by the European Union--NextGenerationEU under the Italian Ministry of University and Research (MUR) National Innovation Ecosystem grant ECS00000041 VITALITY, and the MUR Extended Partnerships grant PE00000001--RESTART. We acknowledge Universita degli Studi di Perugia and MUR for support within the projects VITALITY and RESTART.  
**Data Availability Statement**: The data presented in this study are available on request from the corresponding author.  
**Conflicts of Interest**: The authors declare no conflicts of interest.