As organizations move towards containerization, Kubernetes has emerged as a popular choice for container orchestration. It is a popular open-source platform for automating the deployment, scaling, and management of containerized applications. Moreover, since it is a complex system, understanding its architecture is crucial for deploying and managing containerized applications. In this blog, we will dive deep into the Kubernetes architecture, its components, and best practices.
Kubernetes architecture consists of several components that work together to manage containerized applications in the cluster. These components can be categorised into Control Plane Components and Worker Nodes. Let's explore these components in more detail.
The control plane components manage the overall state of the cluster and make decisions about how to manage and deploy applications in the cluster. The control plane components include:
a. API Server
The API server is the central component of the control plane. It provides an interface for managing the state of the cluster and processing requests from the command-line interface (CLI) and other components.
The API server receives requests from other components, such as kubectl, and processes them by updating the cluster's desired state.
The API server is responsible for authenticating and authorizing requests, validating requests against the Kubernetes API schema, and modifying the state of the etcd datastore.
etcd is a distributed key-value store that stores the configuration data of the Kubernetes cluster. It is the source of truth for the configuration of the cluster, including the configuration of each node, the configuration of services, and the status of running applications. The API server reads from and writes to etcd to maintain the cluster's desired state.
The scheduler is responsible for scheduling containers to run on worker nodes in the cluster. The scheduler uses information about the cluster's resources to make decisions about where to place containers. The scheduler considers factors such as resource requirements, node availability, and application affinity when making scheduling decisions.
d. Controller Manager
The controller manager is responsible for managing controllers that regulate the state of the Kubernetes cluster. Controllers are responsible for maintaining the desired state of the cluster by monitoring and updating the cluster's resources.
It monitors the state of the cluster and takes action to ensure that the desired state of the cluster is maintained. The controller manager includes several controllers, such as the ReplicaSet controller, Deployment controller, and StatefulSet controller.
The worker node components oversee the running of applications in the cluster and provide resources for those applications. The worker node components include:
Kubelet is an agent that runs on each worker node in the cluster. It manages the state of the node and ensures that the containers are running on the node as expected.
It communicates with the API server to receive instructions about which containers to run and how to configure them. Kubelet is responsible for starting, stopping, and managing containers on the node.
kube-proxy is a network proxy that runs on each worker node in the cluster. It is responsible for managing network traffic to and from the containers running on the node. kube-proxy implements a form of network address translation (NAT) to provide a stable IP address for each service in the cluster.
c. Container Runtime
The container runtime oversees the running containers on the worker node. Kubernetes supports multiple container runtimes, such as Docker, rkt, and CRI-O. The container runtime is responsible for downloading container images, creating and managing container filesystems, and starting and stopping containers.
A pod is the smallest deployable unit in Kubernetes. It represents a single instance of an application or service and comprises one or more containers that share the same network namespace and file system. Pods are scheduled to run on worker nodes and are managed by the control plane components.
A service is a Kubernetes resource that provides a stable IP address and DNS name for accessing a set of containers. It allows containers to be accessed by other services within the cluster. Services can be used for load balancing, service discovery, and exposing applications to the outside world.
A deployment is a Kubernetes resource that controls the deployment of a set of containers. It ensures that the desired number of replicas of a container is running at all times. Deployments also provide a way to scale applications horizontally by adding or removing replicas.
Deployments make it possible to roll out new versions of applications and perform rolling updates with zero downtime. They can be updated with new container images or configuration changes without interrupting the service.
A StatefulSet is a higher-level abstraction that is similar to deployment but is designed for stateful applications, such as databases or messaging systems. It ensures that each instance of the application has a stable hostname and network identity, making it easier to manage stateful applications.
In addition to the control plane and worker node components, Kubernetes architecture also includes a set of add-ons that provide additional functionality to the cluster. These add-ons include:
DNS (Domain Name System) enables the communication between pods and services within a cluster. Kubernetes uses a built-in DNS service that maintains a record of all the services and their corresponding IP addresses, which enables pods to communicate with each other using the service name. Kubernetes also allows users to customize the DNS configuration to meet specific requirements. For example, users can configure DNS policies to restrict access to specific services or domains.
Kubernetes Dashboard is a user interface that provides a visual representation of the cluster's resources and components. The dashboard displays information about the state of the cluster, such as the number of pods, nodes, and services running in the cluster. It also allows users to perform administrative tasks, such as scaling pods, creating new deployments, or managing access controls. The dashboard is accessible via a web browser and also provides a user-friendly interface for managing and monitoring the cluster.
c. Ingress Controller
The Ingress controller is a Kubernetes resource that controls external access to services running inside a cluster. It acts as a reverse proxy and routes traffic to the appropriate service based on the URL path or hostname. The Ingress Controller supports multiple routing rules and can handle HTTP, HTTPS, and TCP traffic. It allows users to define custom routing rules to direct traffic to different services based on their URL paths, domain names, or other attributes. The Ingress Controller supports multiple implementations, including Nginx, Traefik, and Istio, each with its unique features and capabilities.
d. Storage Plugins
Storage Plugins are add-on components that provide storage options for containerized applications running in a cluster. Kubernetes supports multiple storage plugins, including hostPath, emptyDir, NFS, GlusterFS, and many others. These plugins provide different storage options, ranging from local storage to cloud-based storage systems. The Storage Plugins allow users to define persistent storage volumes for applications and manage them dynamically. This means that when a pod is terminated or rescheduled, the storage volume assigned to it can be automatically attached to the new pod, ensuring data continuity.
Now, that you've grasped a basic understanding of Kubernetes architecture, here are a few key benefits of this technology.
Due to these benefits offered by Kubernetes architecture, it is one of the most favoured DevOps tools for containerized applications.
Here are some best practices for designing a Kubernetes architecture:
By following these best practices, you can design a Kubernetes architecture that is scalable, secure, and reliable.
So, Kubernetes architecture is a complex yet crucial system that consists of several components like the control plane components, worker node components, and other add-ons. These components work together to manage and deploy containerized applications. As more and more organizations adopt Kubernetes for managing their containerized applications, the demand for professionals with expertise in Kubernetes is increasing. StarAgile Consulting offers a wide range of DevOps certification courses to help professionals gain the skills and knowledge they need to succeed in their careers. Join our courses today and take the first step towards a successful career in Kubernetes and DevOps.
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