Kubernetes and Docker

What is the pod ? What is a Pod? A Pod is the smallest deployable unit in Kubernetes. It represents one or more containers that: Share the same network (IP, ports) Share storage volumes Run together on the same node Think of a Pod as a wrapper around containers. Manifest yaml file: apiVersion: v1 kind: Pod metadata: name: nginx-pod spec: containers: - name: nginx image: nginx ports: - containerPort: 80 2)what is the replicates? ReplicaSet (Ensure Desired Number of Pods) 🔹 What is a ReplicaSet? A ReplicaSet ensures a specified number of identical Pods are running at all times. 🔹 Why do we use ReplicaSets? High availability Self-healing Automatic Pod recreation =================== apiVersion: apps/v1 kind: ReplicaSet metadata: name: nginx-rs spec: replicas: 3 selector: matchLabels: app: nginx template: metadata: labels: app: nginx spec: containers: - name: nginx image: nginx ==================== What ReplicaSet Does Watches Pods with matching labels If Pod crashes → creates a new one If extra Pod exists → deletes it ===================== Deployment (Production-Grade Controller) 🔹 What is a Deployment? A Deployment is a higher-level object that: Manages ReplicaSets Provides rolling updates Enables rollback 🔹 Why do we use Deployments? Zero-downtime deployments Version control of applications Safe upgrades & rollbacks apiVersion: apps/v1 kind: Deployment metadata: name: nginx-deployment spec: replicas: 3 strategy: type: RollingUpdate selector: matchLabels: app: nginx template: metadata: labels: app: nginx spec: containers: - name: nginx image: nginx:1.25 ports: - containerPort: 80 ======= Docker Fundamentals A. Docker Image 🔹 What is it? A Docker image is a read-only blueprint that contains: Application code Runtime (JVM, Node, Python, etc.) Libraries & dependencies OS user-space 🔹 Why do we use images? Consistent environments Immutable deployments Fast startup 🔹 Where used? Local development CI/CD pipelines Kubernetes Pods 🔹 How implemented? docker pull nginx docker images B. Docker Container 🔹 What is it? A container is a running instance of an image. 🔹 Why do we use containers? Lightweight (vs VM) Fast startup Process isolation 🔹 Where used? Run applications Microservices Batch jobs 🔹 How implemented? docker run -d -p 8080:80 nginx docker ps C. Docker Layers 🔹 What is it? Images are built in layers, each instruction adds a new layer. 🔹 Why layers? Faster builds (cache) Reuse Smaller image sizes 🔹 Where used? Docker build process Registry storage 🔹 How implemented? FROM node:18 COPY . . RUN npm install Each line → one layer. 2️⃣ Dockerfile: Build, Tag, Push Cycle A. Dockerfile 🔹 What is it? A text file containing instructions to build an image. 🔹 Why use it? Automation Reproducibility CI/CD compatibility 🔹 How implemented? FROM python:3.11-slim WORKDIR /app COPY requirements.txt . RUN pip install -r requirements.txt COPY . . CMD ["python", "app.py"] B. Build docker build -t myapp:1.0 . C. Tag docker tag myapp:1.0 mydockerhubuser/myapp:1.0 D. Push docker login docker push mydockerhubuser/myapp:1.0 3️⃣ Container Networking A. Ports 🔹 What is it? Ports allow external access to containers. 🔹 Why needed? Containers are isolated by default. 🔹 How implemented? docker run -p 8080:80 nginx Host 8080 → Container 80 B. Container Networking 🔹 What is it? Docker creates virtual networks. 🔹 Why? Container-to-container communication Isolation 🔹 How implemented? docker network create app-net docker run --network app-net nginx Containers can communicate via container name. C. Health Checks 🔹 What is it? Checks if container is healthy, not just running. 🔹 Why? Auto restart Load balancer decisions Kubernetes readiness/liveness 🔹 How implemented? Dockerfile HEALTHCHECK CMD curl -f http://localhost:80 || exit 1 Runtime docker inspect --format='{{.State.Health.Status}}' 4️⃣ Container Registries A. What is a Registry? A place to store and distribute Docker images. B. Why use registries? Centralized storage CI/CD integration Version control C. Popular Registries Registry Cloud Docker Hub Public Amazon ECR AWS Azure ACR Azure Google GCR GCP D. How to Push to Each 🔹 Docker Hub docker login docker push user/app:tag .