All about Kubernetes Networking
Kubernetes networking offers the advantages of ease and stability over several other networking environments. You must be aware of the model and design of your applications as well as the hosts when assigning Kubernetes to orchestrate them.
Kubernetes was introduced primarily to run distributed systems over a group of interconnected hosts. Kubernetes’ core component is networking, but its implementation is harder than we might expect. Distributed systems allow networking to be a fundamental element of Kubernetes deployment, and they make understanding the Kubernetes networking model easier. This helps to comprehend the process of running, monitoring, and troubleshooting the applications that are running on the Kubernetes network.
The networking model is an enormous universe with plenty of notions and concepts. Most people are unfamiliar with this space and feel uncomfortable while talking about the technologies and terminologies of networking. There are several concepts of networking, both old and new, that are required to be comprehended.
To have in-depth knowledge of the Kubernetes networking model, people also need to understand several networking terminologies that include Network Namespace, Virtual IP Address, The Domain Name System, Container Network Interface, Network Address Translation, Connection Tracking, Packet Mangling Tool, and Classless Inter-Domain Routing.
In this article, we have presented a brief guide on Kubernetes Networking. Through this article, we intend to clarify every technology and terminology that is dependent on Kubernetes. We intend to demystify the complexities of Kubernetes networking. The guide also explains how containers, pods, and services communicate with each other within the k8 network. Even if anyone is unfamiliar with some of the networking terminologies, we hope they will have a decent acquaintance with the networking terms after going through this article.
What is Kubernetes Networking?
Kubernetes, also referred to as “K8s” or “Kube”, is a convenient, open-source system that oversees and operates deployment, scheduling, scaling, and maintenance of containerized computer applications. The Kubernetes network comprises several nodes, pods, and containers and hence it permits every containerization component to communicate with each other and also with other computer applications.
The network platform of Kubernetes is quite different from any other open networking platform. Since the Kubernetes network follows a flat network structure, you will not need to plot ports between the containers and the applications hosts. Another advantage of using Kubernetes is that this platform provides enough space to run distributed systems and share machines among various software applications.
Kubernetes Networking allows the administrators to transfer a large volume of work across all private, public, and hybrid cloud infrastructures. It is used by various developers like Google, Amazon Web Services, and Microsoft Azure to suit software applications with their prerequisite setup and arrangements. While setting up the Kubernetes network can be a difficult task, it is a vital step towards success in deploying Kubernetes. Kubernetes networking is supported by several major container management platforms, including IBM Cloud Kubernetes Service, GitLab, Amazon CloudWatch, OpenShift, Docker EE, and Rancher.
Basics of Kubernetes Networking
You need to be familiar with a few concepts and terms related to Kubernetes. Initially, Kubernetes networking was developed by combining greater components and functionalities. We will discuss the interrelated components of K8s in this segment. If you are familiar with the basics of Kubernetes, you may skip this segment.
Nodes: A Node or the Minions is the smallest component in the Kubernetes cluster. Nodes are machines whose nature varies depending on the cluster; they can be virtual, physical, or metal. The Kubernetes Pods are run on nodes and each node comprises the prerequisite elements that are required to run the Pods.
The nodes of a cluster are monitored by the control plane. The control plane comprises several processes including API server, scheduler, controller manager, etcd. There are three components of a node viz., the kubelet, a container runtime, and the Kube-proxy.
Pods: A Pod is considered to be the atom of Kubernetes and is also the smallest component that can be deployed in the Kubernetes cluster. Kubernetes Pods are a group of containers that have the same IP address, network namespace, and storage resources. Each container residing in a pod can communicate with each other as well. Pods in Kubernetes are built using the Kubernetes API server and positioned by the controllers.
Master Node: As the name suggests, the Master node is the chief component of K8s. The master node can communicate with every other node in the cluster both directly and indirectly. Multiple master nodes can be assigned on a Kubernetes cluster to run the control plane. A master node does the following things:
- Operates the Kubernetes cluster.
- Monitors and manages every node in the cluster.
- Stores data and information of everyone who is a member of the Kubernetes cluster.
- If somehow a node fails to do its job, the master node transfers the workload from that node to another node that is workable.
Containers: Containers are widely practiced standards that are used to store programs that are running in a Kubernetes cluster. Containerization is a practice of building a self-contained environment in Kubernetes. With the help of containerization, several programs and dependencies can be put into one single file. This will make the sharing process easy and the chances of programs getting lost will also decrease.
A container also acts as a virtual machine by sharing its Operating System with other applications in the cluster. A container comprises a CPU, memory, file system, and process space. A Kubernetes container can be connected with other containers, or hosts, or external networks, through the Container Networking Interface (CNI).
Cluster: A node is useful if it works individually but it is more efficient if several nodes work together. A cluster is a group of nodes that are assembled to build a more influential and powerful machine. Unlike nodes, a cluster won’t stop working if an individual node fails to perform. A cluster is capable of handling computational load when several programs are deployed on the cluster simultaneously. Also, if you add or remove a node from the cluster, it will not hamper the ongoing program.
Different Methods of Kubernetes Networking
The above-mentioned components such as Nodes, Pods, Containers, Master Nodes, etc., use different methods or variations to communicate among applications in the Kubernetes network. The different communication methods are:
- Container-to-Container Communication
- Pod-to-Pod Communication
- Pod-to-Service Communication
- Internet-to-Service Communication
1. Container-to-Container Communication
The Container-to-Container Communication module shows how an Ethernet device can be directly connected to a virtual machine via a high-level view. To communicate with other applications, it uses the overlay network model.
The different processes of the machine cycle are operated inside a network namespace. The network namespace possesses network devices, firewall rules, and routes through which it can create a logical networking stack during Kubernetes deployment.
The containers are grouped with pods and each of them shares a network namespace with the other. Each container inside the pod also shares the same port space, port name, and IP address. Hence, the containers can easily communicate with each other via the localhost.
2. Pod-to-Pod Communication
The Pod-to-Pod Communication is accessible for pods that are present in the same node as well as for the pods that are present in other pods. Every node in the Kubernetes cluster has a designated IP address which is unique for all. All pods can communicate among themselves using these IP addresses up to a certain primitive level.
In Kubernetes, when pod-to-pod communication is done, a virtual ethernet device (VED) or a Veth pair is generated to attach the pods inside the nodes. Three different network implementations allow Pod-to-Pod communication in Kubernetes. They are Layer 2 (switching) solution, Layer 3 (routing) solution, and Overlay solution.
The containers in K8s also follow the Pod- to-Pod Networking method to communicate with other containers that are residing in the other pods.
3. Pod-to-Service Communication
A Pod-to-Pod communication is not good enough for communicating through direct addressing. There is too much responsibility and precaution to take when dealing with pod IP addresses unless the communication is short-term. Kubernetes recommends use of service for communication to avoid this problem. A pod can be dynamically switched with a service in Kubernetes, as and when necessary.
Service is an abstraction in which several pods are grouped in such a way that they can be effortlessly reached via a single, fixed DNS name or IP address. Hence, Pod-to-Service Communication is more flexible and efficient. Kubernetes services also allow the creation and deletion of the pod as needed without any complexities. This communication is also very good in in-cluster load balancers and distributing traffic.
4. Internet-to-Service Communication
Kubernetes networking can also be referred to as Internet-to-Service Communication. Importing and exporting services and joining forces with other distributed teams require Internet access. Kubernetes uses Egress and Ingress policies to get external access. Controlling traffic on the network is achieved using whitelisting or blacklisting strategies.
Egress: Egress is a process that allows communication from the Kubernetes service to any peripheral connections. This traffic management policy is achieved through an Internet gateway that seeks help from the Network Address Translation (NAT) to port the IP address of the user with the virtual machine on which the node of the user has been hosted. Communication in this way is done with the help of IP tables and Cluster-IPs.
Ingress: Ingress is just the opposite of Egress which allows communication from the peripheral connections to the Kubernetes service. Ingress does not allow services for every client. It has a set of rules and it also has a list of connections that it allows and which it disallows.
Implementation of Kubernetes Networking
Kubernetes allows both the Overlay and Underlay models to handle the cluster networking. There is no default method by which the networking model of Kubernetes can be implemented. However, the networking administrator imposes several third-party tools to implement the model. The following networking options have been recognized by Gartner as the “visionary and idealistic” in the Magic Quadrant for Data Center Networking Report in 2019.
Flannel: Flannel by CoreOs, is arguably the most widespread Container Network Interface (CNI). It permits a daemon agent, called flanneld, to run under each node. Flannel assigns a subset of IPs for advanced IP address management. It allows several protocols like UDP and VXLAN to forward packets among Kubernetes hosts. The installation and configuration process of Flannel is also easy compared to any other CNI plugin.
Project Calico: Project Calico is a Kubernetes networking policy that aids Wireguard, a fast and modern VPN tunnel, to protect on-the-wire, in-cluster pod traffic in the Kubernetes network. With Calico, you can build a bridge between Kubernetes nodes that reside in the same IP network with a high-performance scalable pod network. The Calico system secures host policies, virtual machines, containers, pods, and nodes. Calico can be deployed across any cloud, virtual machines, applications, and Kubernetes distributions without any abstractions and manual interventions.
Weave Net: Weave Net, a network policy developed by Weaveworks, is one of the fastest-growing CNI plugins available. It is an open-source, cloud-native networking architecture that is known for its easy usage and resilience. When you finish installing Weave Net, it enables a virtual router, called peer, to communicate with each other.
Weave Net is ideal for those who want rich networking without complexities and labor-intensive management. Like Flannel, Weave Net is also easy to set up and has automatic configuration settings.
Cilium: Cilium is another eminent networking policy in the Kubernetes cluster that is known for its performance, flexibility, and power. Like Flannel, Cilium also assigns a daemon agent, called Cilium-agent, to run on each node. The Cilium agent assembles the Berkeley Packet Filter (BPF) and moves them to the kernel. It allows inter-container and inter-host networking. Cilium provides a security policy for high-connection workloads.
Cumulus NetQ: Cumulus NetQ was built based on the fabric validation system and is known for delivering visibility into the native container networking. The users can also modify the networking policy during runtime. Cumulus NetQ can be deployed for encapsulation and routing tasks as it offers superior performance and less interception.
There are other options also to implement the Kubernetes Networking Model. They are Dell EMC, VMware NSX-T, Big Switch Networks’ Big Cloud Fabric, Nuage, OVN, Romana, and Contiv.
Conclusion
Kubernetes networking allows users to easily configure communication between applications that are present in a K8s cluster. Kubernetes networking follows a simple network structure, whose implementation is handled by open-source or third-party tools, such as Flannel, Weave Net, Project Calico, and Cilium.
Moreover, you have to rely on several networking variations to configure the K8s network. Every pod that is present inside the cluster is assigned with an IP address and is capable of communicating with any other pods, hosts, or services in the network.
Kubernetes networking is a broad chapter and it is very hard to cover everything in a single article. However, we tried our best to provide a brief discussion on the topic. We hope this article will be helpful for those who are interested in Kubernetes networking and want to dive into the topic.
Programmers and Developers can also be benefitted from this by gathering more knowledge about Kubernetes workloads, designing, and configuration of the network model. Prepare yourself well and make sure to have a well-organized network plan before starting with the configuration process.