Kubernetes

Kubernetes (often abbreviated as K8s) is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. It allows you to manage containers at scale across clusters of machines in an efficient and automated way.

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✅ What is Kubernetes?

Kubernetes is designed to manage containerized applications in a distributed environment. It provides a framework for running and managing containers (often Docker containers) across clusters of machines. With Kubernetes, you can deploy, scale, and maintain your applications efficiently, ensuring they remain highly available, fault-tolerant, and secure.

👉 Founded: 2014 (Originally by Google) 👉 Maintained by: Cloud Native Computing Foundation (CNCF) 👉 Primary Language: Go (Golang) 👉 Key Functionality: Container orchestration, automated deployments, scaling, monitoring, and self-healing.

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✅ Key Concepts in Kubernetes

Concept	Description
Pod	The smallest and simplest unit in Kubernetes. A Pod can contain one or more containers that share the same network namespace and storage.
Node	A physical or virtual machine that runs one or more Pods. There are two types: Master Node (controls the cluster) and Worker Node (runs application containers).
Cluster	A set of nodes (worker and master nodes) that Kubernetes manages to run applications.
Deployment	A controller that manages the deployment of Pods, ensuring the specified number of Pods are running and updated with new changes.
Service	A logical abstraction that defines a set of Pods and a way to access them, often used for load balancing and networking.
Namespace	A way to divide cluster resources between multiple users or projects. It's useful for environments with many teams or projects.
ReplicaSet	Ensures a specified number of replicas of a Pod are running at any given time. It is often used with Deployments.
StatefulSet	Similar to a Deployment but designed for managing stateful applications (e.g., databases) where each Pod needs a unique identifier or stable storage.
DaemonSet	Ensures that a copy of a Pod is running on every node in a cluster (e.g., for logging or monitoring).
ConfigMap and Secret	Stores configuration data and sensitive information (such as passwords or API keys) for use by Pods.
Ingress	Manages external HTTP(S) traffic to services within a Kubernetes cluster.
Helm	A package manager for Kubernetes, which allows you to define, install, and upgrade complex Kubernetes applications.

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✅ How Kubernetes Works

1. Master Node: The master node manages the Kubernetes cluster and handles the scheduling of containers. It contains components like:

   • Kube-apiserver: The API server, which handles REST requests to manage the cluster.

   • Kube-scheduler: Decides where Pods should run based on resource availability and constraints.

   • Kube-controller-manager: Ensures that the cluster’s desired state matches the actual state.

   • Etcd: A distributed key-value store for storing the cluster’s state data.

2. Worker Node: Worker nodes run the application containers and have components like:

   • Kubelet: An agent that ensures the containers in the Pod are running and healthy.

   • Kube-proxy: Handles networking and load balancing between Pods.

   • Container Runtime: Runs and manages containers (often Docker, containerd, or others).

3. Pods: Containers are grouped together in Pods, which are the smallest units in Kubernetes. A Pod contains one or more containers that share network resources and storage volumes.

4. Deployment: When deploying an application, a Deployment is used to manage the desired number of Pods, scaling them as necessary and handling rolling updates or rollbacks.

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✅ Key Features of Kubernetes

1. Automatic Scaling: Kubernetes can automatically scale applications up or down based on demand, using the Horizontal Pod Autoscaler to adjust the number of Pods based on CPU or memory usage.

2. Self-Healing: Kubernetes ensures that containers are always running and replaces failed or terminated Pods automatically. It also reschedules containers to healthy nodes.

3. Load Balancing: Kubernetes automatically balances traffic across Pods, ensuring high availability and even distribution of workload.

4. Rolling Updates: Kubernetes can perform rolling updates to applications, minimizing downtime by gradually replacing old containers with new ones.

5. High Availability: Kubernetes can distribute Pods across multiple nodes, providing redundancy and fault tolerance. If a node fails, Kubernetes automatically reschedules the affected Pods to healthy nodes.

6. Service Discovery and Load Balancing: Kubernetes manages internal and external networking for your applications, automatically providing DNS names and load balancing for Pods.

7. Declarative Configuration: Kubernetes allows you to define your application’s desired state using YAML or JSON files. It will automatically reconcile the current state to match the desired state.

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✅ Kubernetes Architecture Overview

• Master Node: Controls the Kubernetes cluster and makes decisions about the cluster’s state.

• Worker Nodes: Run the application containers and manage the Pods.

• Kubernetes API Server: Manages all API requests to the cluster and exposes the Kubernetes REST API.

• Kubernetes Controller Manager: Runs controllers that regulate the state of the cluster.

• Scheduler: Decides where Pods should run on the worker nodes.

• Etcd: Stores cluster data, including configurations and state.

• Pod: A group of one or more containers, along with storage resources, a unique network IP, and options for running them.

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✅ Kubernetes vs Docker

While Docker is a platform for building and running containers, Kubernetes is an orchestration system that manages containers at scale. They are often used together but serve different purposes:

Feature	Docker	Kubernetes
Purpose	Containerization of applications	Orchestration of containerized applications
Scope	Manages individual containers	Manages clusters of containers
Use Case	Build, ship, and run containers	Manage container clusters and workloads
Scaling	Manually scale containers	Automatically scale containers
Orchestration	Not provided (requires additional tools)	Built-in orchestration and management
Networking	Limited to individual containers	Advanced networking across containers and nodes

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✅ Kubernetes Use Cases

1. Microservices Architecture: Kubernetes is widely used to manage microservices-based applications, where each service is containerized and deployed as a separate Pod.

2. CI/CD Pipelines: Kubernetes can automate the deployment of containerized applications, integrating well with CI/CD pipelines to ensure seamless updates and scaling.

3. Cloud-Native Applications: Kubernetes is ideal for applications that require portability, scalability, and fault tolerance across cloud environments.

4. Hybrid Cloud: Kubernetes allows seamless workload management across multiple cloud providers or on-premises data centers, providing flexibility and resilience.

5. Batch Processing: Running large-scale batch jobs in Kubernetes can efficiently distribute and manage workloads across containers.

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✅ Basic Kubernetes Commands

Command	Description
kubectl version	Displays the version of Kubernetes and kubectl client.
kubectl get pods	Lists the Pods in the cluster.
kubectl get services	Lists all services running in the cluster.
kubectl apply -f <file>.yaml	Applies a Kubernetes configuration file to create or update resources.
kubectl describe pod <pod_name>	Displays detailed information about a specific Pod.
kubectl delete pod <pod_name>	Deletes a Pod from the cluster.
kubectl logs <pod_name>	Fetches the logs from a specific Pod.
kubectl scale deployment <deployment_name> --replicas=<num>	Scales a Deployment to the specified number of replicas.
kubectl get nodes	Lists the nodes in the cluster.
kubectl create -f <file>.yaml	Creates resources (Pods, Deployments, Services, etc.) from a YAML file.

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✅ Kubernetes Ecosystem and Tools

• Helm: A package manager for Kubernetes, which helps you define, install, and upgrade applications using Helm charts.

• Kubernetes Dashboard: A web-based user interface for managing and monitoring Kubernetes clusters.

• Kubeadm: A tool that helps set up Kubernetes clusters.

• Prometheus & Grafana: Used for monitoring and alerting within Kubernetes clusters.

• Istio: A service mesh that provides features like traffic management, security, and observability for microservices in Kubernetes.

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✅ Conclusion

Question	Answer
What is Kubernetes?	Kubernetes is an open-source container orchestration platform that automates deployment, scaling, and management of containerized applications.
What does Kubernetes manage?	Kubernetes manages clusters of nodes, containers, and application deployments, ensuring high availability, scalability, and fault tolerance.
What is a Pod?	A Pod is the smallest deployable unit in Kubernetes and can contain one or more containers.
Why use Kubernetes?	Kubernetes allows for automated scaling, self-healing, and efficient management of containerized applications across large, distributed environments.