Kubernetes Architecture: Understanding Core Components

In the era of modern software development and deployment, Kubernetes stands as the standard tool for orchestrating containerized applications in DevOps methodology. Its robust architecture not only simplifies the management of containerized workloads but also empowers teams to scale, deploy, and manage applications seamlessly across diverse environments. According to Statista “In 2022, 61 per cent of respondents state using Kubernetes. 50 per cent of respondents to a global survey of DevOps, engineering, and security professionals stated that Red Hat OpenShift is the Kubernetes platform they primarily use. “

Before using Kubernetes for deployment, we have to understand the architecture and working of it. In this blog, we are going to understand the workings of Kubernetes, its components, and a lot more.

Table of Contents:

• What Is Kubernetes?
• Kubernetes Architecture Diagram
• Kubernetes Components
• Control Plane Components
• Node Components
• Kubernetes Architecture Explained

What Is Kubernetes?

Kubernetes, popularly known as Kube or K8s, is an open-source container orchestration tool used for automating, scaling, and management of containerized applications.

Kubernetes was originally developed by Google and was first released in 2014. It is officially written in the Go Programming Language. Later, the Cloud Native Computing Foundation (CNCF), a joint venture of Google and Linux Foundation, worked together with the community to maintain Kubernetes.

Example of Kubernetes Use Case:

• Engineers and finance can determine exactly where, when, and how Kubernetes expenditures are incurred. They can check Kubernetes costs, assure high availability in service delivery, and more by monitoring Kubernetes appropriately.  

Kubernetes Architecture Diagram

Kubernetes works on the principle of client-server architecture, where there are master and slave nodes. The master node is often installed on a single Linux system while the slave node is installed on Linux workstations. Below is a diagram representing the architecture of Kubernetes:

Kubernetes Components

There are many components in Kubernetes. All the components can be grouped under two major categories:

1. Control Plane Components:  The control plane components are responsible for container orchestrations. It helps to maintain the state of a cluster.
2. Node Components: The node components are a very critical component in Kubernetes, responsible for running the containerized applications.

Control Plane Components

The control plane acts as a nerve centre for Kubernetes for container orchestration and maintaining the state of the cluster. There are a total of 5 services that run on the control plane.

1. Kube-API Server

The Kube API server is one of the most important parts of the Kubernetes control plane. It functions as the primary interface for communication with the cluster. It takes commands and updates from Kubectl, CLI, and other tools and it is a security wall to all incoming traffic. All these requests are then authenticated prior to being transmitted to other parts of the system in order to ensure that both the integrity and safety of the cluster are maintained. In a nutshell, every action within the cluster must go through the API server, making this component central and vital in Kubernetes operations.

2. Etcd

The Kubernetes clusters’ vital information like pod status and namespace configuration is managed by etcd, a purpose-built distributed key-value data storage component. Security is important to restrict the accessibility of this component only to the API server. The watch capability of etcd is utilized by the Kubernetes API server in order to keep a close eye on any changes concerning object states.

3. Kube-Scheduler

When the API Server receives a request for scheduling pods, it forwards the task to the Scheduler which aims at making informed choices on best node placement aimed at improving cluster efficiency. Suitable worker nodes are identified by the Kube scheduler based on factors like pod requirements such as CPU, memory, and affinity in order to ensure effective resource allocation.

There are several ways Kubernetes uses to schedule a pod. First of all, it goes through every node available and picks out the ones that are best suited for the pod. The scheduling plugins rank the nodes in order to assist the scheduler in selecting the node that has the capability of binding the pod throughout its obligations. This enables a more precise ordering of high-priority pods and also enables an easier way to embed custom plugins which in other words is a new approach towards handling pods in Kubernetes.

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4. Kube-Controller Manager 

The Kube-controller-manager supervises the process of execution of controllers that are used for all different phases of control loops of a cluster.

There are many kinds of controllers existing. Below are a few of them:

• Deployment Controllers are responsible for the deployment of the set of replicas of containerized applications.

• Replication Controllers ensure that a specified quantity of pod replicas are always available, automatically replacing any failed pods.

• StatefulSet Controllers can provide broad and narrow application storage, unique network identifiers, application deployment and scaling, and many more.

• DaemonSet Controllers ensure that all the Pods of specified types exist in all servers of the cluster or only in those that have the required label.

5. Cloud-controller-manager  

In the case of Kubernetes deployments in the cloud, the communication between the Kubernetes cluster and the APIs of the Cloud Computing Platform is facilitated by the cloud controller manager. It makes it possible for the fundamental units of Kubernetes to be plug-and-play components that are able to interact with the relevant cloud providers.

For example, if a user is using the Amazon Web Services (AWS) infrastructure, the cloud controller manager enables users to manage Kubernetes and the AWS APIs at the same level. It makes it possible for such services as EC2 instances, ELBs, and EBS volumes to work and integrate in a much broader scope.

Node Components

The node components are the current set in the individual nodes which are utilized for storing and executing the pods thus giving the Kubernetes the execution environment. There are all three services which are available on every node which is used for controlling the pods.

1. Kubelet

 As part of the cluster, a Kubelet is seen as an agent that is installed on every single node of the cluster. It is in charge of overseeing the containers that are within the Pod.

2. Kube-proxy 

Each node in the cluster contains kube-proxy, which is a network proxy, and doing that is crucial in implementing the idea of the Kubernetes Service.

3. Container Runtime

Matters of container execution fall to this element termed container, which is a vital element in allowing Kubernetes to be able to run containers successfully within its environment.

Addons

In addition to the core components, there are minimal additional components that need to be added to ensure that the Kubernetes cluster is working at an optimal level. The selection of these components and add-ons depends on the goals and the requirements of the project in question.

Numerous add-ons augment the capabilities of the Kubernetes cluster, including DNS, Web UI, container-level monitoring, cluster-level logging, and network plugins that are required in the cluster.

1. DNS

In conjunction with all the existing DNS servers within your setup, Cluster DNS emerges as a new DNS server that specifically focuses on providing DNS records for Kubernetes services.

2. Web UI (Dashboard)

The dashboard acts as a web application for the configuration and troubleshooting of applications and the cluster itself in the scope of Kubernetes clusters.

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3. Container Resource Monitoring

Container Resource Monitoring focuses on capturing a set of relevant time series metrics of containers, puts them into storage in the back-end database, and also offers an easy-to-use front end for data searching.

4. Cluster-level Logging

The component responsible for this is called the cluster-level logging functionality which logs container logs into the storage and enables to perform search and browse logs.

5. Network Plugins

Network plugins are important software pieces that comply with the container network interface (CNI) specifications. They enable pods to be assigned IP addresses and communicate with each other within the cluster.

Kubernetes Architecture Explained

Here’s how Kubernetes works:

• The Desired State is Defined: The Desired State is Defined: A Kubernetes manifest file is produced, which indicates the specification of how the application is supposed to be configured. The manifest may include such information as the container image to use, how many replicas are needed, the service network and its storage development requirements, environment variables, or command line arguments to configuration settings.
• Submit the Manifest File: A still intended state is submitted to the Kubernetes API server, which acts as the control plane for this system in the form of a manifest file. This said the desired state is then saved in an etc. distributed key-value store by the API server.
• Control Plane Components: Kubernetes implements several control plane elements which in their functioning, are expected to interact in the correct timing to maintain the proper functioning of the cluster. These include controller manager, etc, and API server.
• Scheduler: The Kubernetes includes pods, which are basic deployable units that can be scheduled. The pod Scheduler waits for new pods and thereafter schedules them for execution on a cluster of computers with regard to available resources and other scheduling policies.
• Kubelet: The Kubelet is part of Kubernetes and is responsible for the management of all the containers and pods that are running on each of the nodes in the cluster. This Kubelet talks to the API server to ensure that the required state of Running pods is achieved.
• Container Runtime: Kubernetes allows you to integrate with different types of container runtimes such as the Docker Container for managing the nodes’ active containers.
• Networking: Within k8s, there is an internal communication networking model that enables containers to communicate across different nodes. In addition, load balancing and network address translation means that services provided in the cluster can be made available to clients located outside the cluster.
• Updates and Scaling: There are updates and scaling functionalities that can be used such as editing non-functioning applications with zero downtime, restoring erased directories, making sub-teams, and controlling your users or adjusting the scale of resources within the system based on the amount of demand it receives.

Conclusion

We are optimistic that this blog has been able to address the user’s concerns related to the Kubernetes Architecture, how it operates, and what its components and extensions are. For more such content, you can check out our YouTube channel as well.

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