Docker Fundamentals Kubernetes

What You’ll Learn 📚

• Core concepts of Docker and Kubernetes
• Key terminology and definitions
• Simple to complex examples
• Common questions and answers
• Troubleshooting tips

Introduction to Docker and Kubernetes

Docker is a platform that allows developers to package applications into containers—standardized executable components that combine application source code with the operating system libraries and dependencies required to run that code in any environment. Kubernetes is an open-source system for automating the deployment, scaling, and management of containerized applications. Think of Docker as the tool to create containers and Kubernetes as the tool to manage them.

Key Terminology

• Container: A lightweight, standalone, executable package of software that includes everything needed to run it.
• Image: A read-only template used to create containers.
• Pod: The smallest deployable units of computing in Kubernetes, which can contain one or more containers.
• Cluster: A set of nodes (machines) that run containerized applications managed by Kubernetes.

Getting Started with Docker

Simple Example: Hello World

# Pull the hello-world image from Docker Hub
docker pull hello-world

# Run the hello-world container
docker run hello-world

Progressively Complex Examples

Example 1: Running a Simple Web Server

# Pull the nginx image
docker pull nginx

# Run the nginx container
docker run -d -p 8080:80 nginx

Example 2: Building a Custom Docker Image

# Create a Dockerfile
# Use the official Python image as a parent image
FROM python:3.8-slim

# Set the working directory in the container
WORKDIR /app

# Copy the current directory contents into the container at /app
COPY . /app

# Install any needed packages specified in requirements.txt
RUN pip install --no-cache-dir -r requirements.txt

# Make port 80 available to the world outside this container
EXPOSE 80

# Run app.py when the container launches
CMD ["python", "app.py"]

Introduction to Kubernetes

Simple Example: Deploying a Pod

# Create a YAML file for a simple pod
apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
spec:
  containers:
  - name: nginx
    image: nginx

Progressively Complex Examples

Example 1: Deploying a Deployment

# Create a YAML file for a deployment
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx

Example 2: Creating a Service

# Create a YAML file for a service
apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80

Common Questions and Answers

1. What is the difference between Docker and Kubernetes?

   Docker is used to create and run containers, while Kubernetes is used to manage and orchestrate those containers across a cluster of machines.

2. Why use containers instead of virtual machines?

   Containers are lightweight and share the host system’s kernel, making them faster to start and more efficient in resource usage compared to virtual machines.

3. How do I install Docker?

   Visit the official Docker documentation for installation instructions specific to your operating system: Get Docker.

4. What is a Kubernetes cluster?

   A Kubernetes cluster is a set of nodes that run containerized applications managed by Kubernetes. It consists of a control plane and one or more worker nodes.

5. How do I scale an application in Kubernetes?

   You can scale an application by adjusting the number of replicas in a deployment. Use the kubectl scale command or update the deployment YAML file.

Troubleshooting Common Issues

If you encounter issues with Docker not starting, check if the Docker daemon is running. You can restart it using sudo systemctl restart docker on Linux.

Lightbulb moment: Remember, Docker is like a shipping container for your code, and Kubernetes is the port authority managing all the containers!

For more detailed troubleshooting, refer to the official Docker and Kubernetes documentation.

Practice Exercises

• Try creating a Dockerfile for a simple Node.js application and build an image from it.
• Deploy a multi-container application using Kubernetes and expose it using a service.
• Experiment with scaling a Kubernetes deployment up and down.

Remember, practice makes perfect! Keep experimenting and don’t hesitate to reach out to the community for help. Happy coding! 🎉