What is Kubernetes?

Introduction to Kubernetes (K8s)

Kubernetes (often abbreviated as K8s) is an open-source container orchestration platform originally designed by Google. It automates the deployment, scaling, and management of containerized applications (like Docker containers).

When your application grows and you need to run hundreds of containers across dozens of physical or virtual machines, managing them manually becomes impossible. That's where Kubernetes shines.

Kubernetes Architecture

A Kubernetes environment consists of multiple machines working together. This group of machines is called a Cluster. The cluster is split into two primary roles:

1. The Control Plane (Master Node)

Think of the Control Plane as the "brain". It maintains the desired state of the cluster, schedules containers, and monitors machine health.

• kube-apiserver: The frontend of the cluster. Every command you run goes through the API server.
• etcd: A consistent, highly-available key-value store containing all cluster data.
• kube-scheduler: Watches for newly created Pods with no assigned node, and selects a node for them to run on.
• kube-controller-manager: Runs controller processes that watch the cluster state (acting like a thermostat).

2. Worker Nodes

Worker nodes are the actual workhorses where your application containers run.

• kubelet: An agent running on each node ensuring that containers are running in a Pod.
• kube-proxy: Maintains network rules on nodes allowing communication to your Pods from network sessions.

What is a Pod?

In Kubernetes, you don't run containers directly. Instead, containers are wrapped inside Pods.

A Pod is the smallest and most basic deployable object in Kubernetes. It represents a single instance of a running process in your cluster.

• A Pod usually contains one container.
• However, it can contain multiple containers that are tightly coupled and share the same network namespace and storage volumes.

Creating Your First Pod

Normally, you define Kubernetes resources using declarative YAML files.

yaml
# nginx-pod.yaml
apiVersion: v1
kind: Pod
metadata:
  name: my-first-pod
  labels:
    app: webserver
spec:
  containers:
    - name: nginx-container
      image: nginx:latest
      ports:
        - containerPort: 80

You apply this file to your cluster using the CLI tool kubectl:

bash
kubectl apply -f nginx-pod.yaml

Next Steps

While creating raw Pods is helpful for learning, production applications never run bare Pods because if a Pod dies, it doesn't restart automatically! To fix this, we use higher-level controllers.