What is the difference between Docker ADD and COPY?

Example:

COPY config.json /app/config.json
ADD myapp.tar.gz /app/

How do you optimize Docker images?

• Use smaller base images (e.g., alpine instead of ubuntu).

• Multi-stage builds to reduce image size:

  FROM node:16 AS build
  WORKDIR /app
  COPY . .
  RUN npm install && npm run build
  
  FROM nginx:alpine
  COPY --from=build /app/dist /usr/share/nginx/html

• Use .dockerignore to avoid unnecessary files.

What is the difference between Docker ENTRYPOINT and CMD?

• ENTRYPOINT is not overridden by command-line arguments, while CMD can be.
• Best practice: Use ENTRYPOINT for fixed commands.

Example:

ENTRYPOINT ["nginx", "-g", "daemon off;"]
CMD ["-p", "80"]

How do you debug a running Docker container?

• Get container logs: docker logs my-container
• Attach to a running container: docker exec -it my-container /bin/sh
• Inspect container details: docker inspect my-container

What is a Docker Multi-Stage Build?

A multi-stage build reduces image size by using multiple FROM statements.

FROM golang:1.17 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp

FROM alpine
COPY --from=builder /app/myapp /myapp
ENTRYPOINT ["/myapp"]

The final image only contains the built binary.

How does Docker handle networking?

• Bridge network (default): Containers communicate via virtual network.
• Host network: Container shares the host's networking stack.
• Overlay network: Used in Docker Swarm for multi-host networking.

Example:

docker network create mynetwork
docker run --network=mynetwork nginx

What is the difference between Docker Swarm and Kubernetes?

How do you remove unused Docker images and containers?

docker system prune -a

This removes stopped containers, unused networks, and dangling images.

What is Docker BuildKit?

Docker BuildKit improves build speed and caching.
Enable it with:

DOCKER_BUILDKIT=1 docker build .

Benefits:
✅ Faster builds
✅ Parallel execution
✅ Improved caching

How do you limit container resource usage?

Use --memory and --cpus:

docker run --memory=512m --cpus=1 nginx

This limits memory to 512MB and CPU usage to 1 core.

How does Kubernetes handle high availability?

• Uses multiple master nodes to avoid single points of failure.
• Deployments use replica sets to keep applications running.
• Load balancing & failover mechanisms ensure availability.

What is the role of kubelet in Kubernetes?

Kubelet runs on each node and:
✅ Communicates with the master node
✅ Ensures containers are running
✅ Monitors container health

How do you check logs of a running Pod in Kubernetes?

kubectl logs my-pod
kubectl logs -f my-pod  # Stream logs in real-time

What are Kubernetes Labels and Selectors?

Labels identify resources, while selectors filter resources.
Example:

metadata:
  labels:
    app: my-app

To filter pods by label:

kubectl get pods -l app=my-app

What is a Kubernetes Ingress?

An Ingress manages external access to services.
Example:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: my-ingress
spec:
  rules:
  - host: myapp.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: my-service
            port:
              number: 80