## 3 Technology, Hardware and Software of Edge Computing
### Virtual Technology of Containers  
Containers have become a widely adopted method for running applications in EC. However, before an application can be launched, the end node must download the container image, which consists of various layers. Due to the limited bandwidth available in EC environments, the initialization latency due to long download times can significantly impact real-time performance. To mitigate this, ref. [88] proposes a specific sequence for container assignment and layer downloads to minimize initialization latency. While layers in Docker images are not entirely identical, ref. [89] argues that reorganizing the Docker image layers to maximize their overlap can reduce both storage and network consumption. Furthermore, ref. [90] emphasizes that integrating MEC, network function virtualization (NFV), and container-based virtualization technology (CVT) in 5G networks provides low latency, high bandwidth, and agility, creating a flexible and resilient network compatible with IoT devices. In [91], lightweight virtualization technologies are explored in IoT and MEC environments to enhance container efficiency on low-power devices. Additionally, virtualization in Edge/Fog servers supports scalable and high-performance services, as illustrated in Figure 4, which highlights the effectiveness of mechanisms that provide on-demand services by launching customized VMs or containers [92]. Virtualization, or containerization at the operating system level, is commonly used to separate process groups [93]. Prominent projects in this area include Docker (San Francisco,  
Figure 4: Virtualization layers and components in EC Architecture [92]. CA, USA), LXC (Global), CoreOS (San Francisco, CA, USA), LMCTFY (Google, Mountain View, CA, USA), and Apache Mesos (San Francisco, CA, USA). Compared to hypervisor-based virtualization, container technology allows for more efficient use of system resources by minimizing overhead and providing a lighter abstraction layer. Hypervisors operate full virtual machines with dedicated operating systems, whereas containers share the host OS, leading to faster performance and reduced resource consumption [94]. In contrast, container technology enables more efficient use of system resources, reducing the overhead. To enhance flexibility and scalability in application management, container-based virtualization is often utilized in distributed and resilient edge clusters. For instance, Kubernetes (Mountain View, California, USA) and Apache Kafka (San Francisco, California, USA), both leveraging containerization, are implemented in such clusters [95]. Cloud environments favor containerization over hypervisor-based virtualization due to its reduced overhead and more efficient resource utilization. A similar security architecture is proposed in [96] to secure cloud environments using hypervisor-based virtualization. However, cloud providers are progressively adopting containerization to deliver faster and more scalable services by integrating virtualization technologies with self-service capabilities over network infrastructures. In FC, virtual machines in cloud environments are insufficient to meet the requirements of fog nodes. Therefore, fog nodes use container technology to improve resource utilization and reduce service latency [97]. Docker is the most widely adopted container technology, directly managed by the main kernel [98]. Docker containers are configured through the command line interface (CLI) and Dockerfile, which contains all executable source code, libraries, and dependencies required for initialization. ARM architectures--commonly used in mobile and low-power systems--are supported by container platforms like Docker and Kubernetes. Docker facilitates the creation of images specifically designed for ARM32 or ARM64 systems. Popular repositories such as Docker Hub provide optimized container images for these platforms. Table 4 illustrates the compatibility of container technologies with ARM-based edge hardware.