说明

Underlay和Overlay是两种不同的网络架构概念，用于实现网络通信和隔离。

Underlay（底层网络）是实际物理设备和网络基础设施，例如交换机、路由器和网络电缆等。Underlay网络负责将数据包从一个物理设备传输到另一个物理设备，提供物理连接和传输能力。

Overlay（覆盖网络）是在Underlay网络之上构建的逻辑网络，通过在Underlay网络上添加虚拟化层来实现。Overlay网络可以跨越多个物理设备，将其抽象为逻辑的网络层，并提供各种网络功能和服务，如网络隔离、多租户支持和安全性等。

在Underlay网络中，数据包使用物理设备之间的直接连接进行传输。而在Overlay网络中，数据包从源设备出发，经过Overlay网络的虚拟化层，通过Underlay网络传输到目标设备，并在目标设备上解封装。

使用Underlay网络时，网络的布局和配置直接依赖于底层物理设备和协议。而使用Overlay网络时，网络的配置和管理更加灵活，可以根据需要创建和配置虚拟网络，不受底层物理设备的限制。

Underlay和Overlay网络架构在实际应用中可以相互结合，以提供更强大和灵活的网络功能。Underlay网络提供物理连接和传输能力，Overlay网络提供逻辑性和可编程性，结合起来可以实现虚拟化、隔离和安全等高级网络功能。

On K8s内部应用场景

在Kubernetes (K8s) 中，Underlay和Overlay在网络架构中也扮演着不同的角色。

Underlay网络是指Kubernetes集群底层的物理网络基础设施，它负责传输网络流量，连接各个节点和设备。这可以是物理子网、虚拟机网络或其他基础网络设施。Underlay网络通常由云服务提供商、物理网络设备和网络协议来管理。

Overlay网络是建立在Underlay网络之上的逻辑网络层，它为Kubernetes集群中的Pod和Service提供虚拟的网络环境。Overlay网络主要用于实现多租户的网络隔离、服务发现和负载均衡等功能。在K8s中，常用的Overlay网络方案包括Flannel、Calico、Weave和Cilium等。

在Kubernetes中，Underlay和Overlay网络的协同工作被用于实现以下功能：

• Pod网络通信：Kubernetes集群中的Pod通过Overlay网络进行通信。每个Pod都被分配一个唯一的IP地址，并通过Overlay网络在不同的节点之间进行跨节点通信。
• 服务发现和负载均衡：Kubernetes中的Service通过Overlay网络公开服务，并自动进行负载均衡。负载均衡器会将流量分发给后端Pod，实现服务的高可用和扩展性。
• 多租户隔离：Kubernetes支持多个租户共享同一个集群，并通过Overlay网络实现网络隔离。每个租户的Pod被保持在自己的虚拟网络中，使其与其他租户的Pod隔离开来。
• 网络策略和安全性：通过Overlay网络，Kubernetes可以实现网络策略，限制Pod之间的通信，并提供安全性。网络策略规则可以基于IP地址、标签或服务端口等进行配置。

总结来说，在Kubernetes中，Underlay网络提供物理网络基础设施和传输能力，而Overlay网络在其之上构建虚拟的网络层，为容器提供多租户隔离、服务发现和网络安全等高级功能。通过Underlay和Overlay的结合使用，Kubernetes提供了灵活可靠的网络环境，支持大规模容器化应用的部署和管理。

On the other hand

Once upon a time, in the vast universe of cyberspace, there existed two remarkable worlds known as Underlay and Overlay.

Underlay was a hidden realm, consisting of a complex network infrastructure that formed the foundation of communication between devices and networks across galaxies. It was a marvel of technology, with countless interstellar cables and nodes spread across the cosmos. Underlay represented the physical layer of connectivity that allowed information to travel from one point to another seamlessly, much like the cosmic forces that held galaxies together.

Overlay, on the other hand, was a mystical dimension that floated above Underlay. It was a virtual layer, existing independently of the physical network infrastructure. In Overlay, ethereal beings known as software-defined entities dwelled. These entities possessed extraordinary capabilities to manipulate and optimize data flows, transcending the limitations of physical networks. Overlay was akin to a realm of magic, where the laws of physics could be rewritten.

Over time, the denizens of Underlay and Overlay realized the potential for collaboration. They understood that by harnessing the power of both worlds, they could achieve the ultimate network architecture, capable of revolutionizing communication as they knew it.

Thus, the concept of Underlay and Overlay integration was born. Like characters from different realms in a science fiction saga, Underlay and Overlay joined forces to create a harmonious universe of interconnectivity. By combining the reliability and stability of Underlay with the agility and flexibility of Overlay, they formed a synergistic alliance, capable of delivering unparalleled experiences across the vast expanse of cyberspace.

Together, Underlay and Overlay embarked on an epic journey to aid the inhabitants of the universe. They connected distant galaxies, enabling seamless communication between civilizations. They conquered the challenges of latency and congestion, ensuring that information flowed effortlessly across vast distances. They even transcended boundaries, allowing beings from different dimensions to interact and collaborate.

With their combined powers, Underlay and Overlay formed a cosmic fabric, weaving together the intricate threads of connectivity in the galaxy. This fusion of technology and imagination led to a new era of network architecture, capable of supporting the ever-expanding universe of data and powering the dreams of those who navigated the stars.

And so, the story of Underlay and Overlay became a legend passed down through the ages, reminding us that when different worlds come together, they can create something extraordinary.