Kubernetes, often abbreviated as K8s is an open-source container orchestration platform that helps manage and deploy containerized applications. It automates the deployment, scaling, and management of containerized applications and services, and makes it easier to run and manage these applications in a cloud environment. Kubernetes provides a way to manage and scale applications by dividing them into small, independent units called containers. Containers are bundled with all the necessary software dependencies, libraries, and configuration files, making them easily portable across different computing environments. Kubernetes helps automate the deployment of these containerized applications, by providing features like load balancing, automatic scaling, self-healing, and rolling updates. This allows organizations to easily deploy and manage complex, distributed applications in a scalable and reliable way.
Benefits
Scalability: Kubernetes provides automated scaling features that allow applications to easily scale up or down based on demand.
High availability: Kubernetes ensures that applications are always available by providing self-healing, automatic failover, and load balancing features.
Portability: Kubernetes makes it easy to run containerized applications on different computing environments, including on-premises data centers, public clouds, and hybrid environments.
Flexibility: Kubernetes provides a flexible platform for running containerized applications, allowing developers to use different programming languages, frameworks, and tools.
Automation: Kubernetes automates many tasks involved in deploying, scaling, and managing containerized applications, freeing up developers and operations teams to focus on higher-level tasks.
Ecosystem: Kubernetes has a large and growing ecosystem of tools and services that integrate with the platform, making it easier to use and extend.
Architecture
Kubernetes has a modular architecture that consists of two main components
Master The control plane is responsible for managing the overall state of the Kubernetes cluster. It consists of several components, including:
API server: The API server is the primary management component of Kubernetes. It exposes the Kubernetes API, which allows users to interact with the cluster, and it manages the state of the cluster by storing information about resources and their desired state.
etcd: etcd is a distributed key-value store that stores the state of the Kubernetes cluster. It is used by the API server to store configuration data, metadata, and other important information.
Scheduler: The scheduler is responsible for scheduling pods to run on worker nodes. It considers factors like resource requirements, node affinity, and anti-affinity when making scheduling decisions.
Controller manager: The controller manager is responsible for managing controllers that are responsible for ensuring that the current state of resources matches their desired state.
Worker nodes: The worker nodes are where containerized applications run, and they are managed by the control plane. Each worker node runs several components including:
Kubelet: The kubelet is responsible for managing the state of pods on a single node. It communicates with the API server to retrieve pod definitions and ensure that the pods are running as expected.
Container runtime: The container runtime is responsible for running containers within pods.
kube-proxy: The kube-proxy is responsible for managing network connectivity between pods and between nodes.
Pod: The pod is the smallest deployable unit in Kubernetes. It consists of one or more containers that share a common network namespace and file system, and it is scheduled to run on a worker node.
Difference between kubectl and kubelets.
kubectl
kubectl is a command-line interface (CLI) tool that allows users to interact with the Kubernetes API server.
It is typically used for deploying, managing, and troubleshooting applications running on a Kubernetes cluster.
kubectl is installed on a client machine (such as a laptop or desktop) and communicates with the API server over the network.
Users can run kubectl commands from a command line on any machine that has access to the Kubernetes cluster.
kubectl is used to create and manage Kubernetes objects such as pods, services, and deployments.
kubelet
kubelet is a node agent that runs on each worker node in a Kubernetes cluster.
Its primary responsibility is to ensure that the containers running on the node are healthy and running as expected.
kubelet communicates with the API server to retrieve the desired state of the containers running on the node and ensures that the actual state matches the desired state.
It is responsible for starting and stopping containers, monitoring their health, and reporting back to the API server.
kubelet manages the networking and storage resources for containers running on the node.
API Server in Kubernetes:
Provides a RESTful API interface for managing and interacting with the Kubernetes cluster.
Responsible for authentication, authorization, validation, data storage and retrieval, resource management, and communication with other components.
Manages the lifecycle of Kubernetes resources such as pods, services, and deployments.
Stores the configuration data and state of the Kubernetes cluster in etcd.
Critical component of the Kubernetes Control Plane.