Docker Command Line Interface (CLI) Basics

What You’ll Learn 📚

• Introduction to Docker and its CLI
• Core Docker CLI commands
• Practical examples and exercises
• Common questions and troubleshooting tips

Introduction to Docker

Docker is a platform that allows developers to automate the deployment of applications inside lightweight, portable containers. Think of a container as a small, self-contained environment that includes everything your application needs to run. This makes it super easy to move your applications between different environments without worrying about compatibility issues. 🐳

Why Use Docker?

• Consistency: Containers ensure that your application runs the same way, regardless of where it’s deployed.
• Efficiency: Containers are lightweight and use fewer resources than traditional virtual machines.
• Portability: Easily move containers between different environments.

Key Terminology

• Image: A read-only template used to create containers. Think of it as a blueprint for your application.
• Container: A runnable instance of an image. It’s where your application lives and runs.
• Dockerfile: A text file that contains instructions on how to build a Docker image.
• Registry: A storage and content delivery system, like Docker Hub, where Docker images are stored and shared.

Getting Started with Docker CLI

Setup Instructions

Before we begin, make sure you have Docker installed on your machine. You can download it from the Docker website. Once installed, open your terminal and run the following command to verify the installation:

docker --version

Your First Docker Command

docker run hello-world

Progressively Complex Examples

Example 1: Running a Simple Web Server

Let’s run a basic web server using the official nginx image.

docker run --name my-nginx -d -p 8080:80 nginx

Example 2: Building a Custom Image

Create a simple Dockerfile to build a custom image.

# Dockerfile
FROM python:3.8-slim
COPY app.py /app.py
CMD ['python', '/app.py']

Build and run the image:

docker build -t my-python-app .
docker run my-python-app

Example 3: Managing Containers

Learn how to list, stop, and remove containers.

# List running containers
docker ps

# Stop a container
docker stop my-nginx

# Remove a container
docker rm my-nginx

Common Questions and Answers

1. What is Docker? Docker is a platform for developing, shipping, and running applications in containers.
2. What is a Docker container? A container is a lightweight, standalone, executable package that includes everything needed to run a piece of software.
3. How do I install Docker? You can download Docker from the Docker website and follow the installation instructions for your operating system.
4. What is a Docker image? An image is a read-only template used to create containers.
5. How do I run a Docker container? Use the docker run command followed by the image name.
6. What is Docker Hub? Docker Hub is a cloud-based registry service for sharing Docker images.
7. How do I stop a running container? Use the docker stop command followed by the container name or ID.
8. How do I remove a container? Use the docker rm command followed by the container name or ID.
9. What is a Dockerfile? A Dockerfile is a text file that contains instructions for building a Docker image.
10. How do I build a Docker image? Use the docker build command followed by the path to the Dockerfile.
11. What is the difference between an image and a container? An image is a blueprint, while a container is a running instance of that image.
12. Can I run multiple containers from the same image? Yes, you can run multiple containers from the same image.
13. How do I list all Docker images? Use the docker images command.
14. How do I list all running containers? Use the docker ps command.
15. How do I remove a Docker image? Use the docker rmi command followed by the image name or ID.
16. What is a Docker registry? A registry is a storage and content delivery system for Docker images.
17. How do I push an image to Docker Hub? Use the docker push command after logging in with docker login.
18. How do I pull an image from Docker Hub? Use the docker pull command followed by the image name.
19. What is the difference between docker run and docker start? docker run creates and starts a new container, while docker start restarts a stopped container.
20. How do I access a running container’s shell? Use the docker exec -it command followed by the container name and /bin/bash or /bin/sh.

Troubleshooting Common Issues

Issue: Docker command not found.
Solution: Ensure Docker is installed and added to your system’s PATH.

Issue: Cannot connect to the Docker daemon.
Solution: Make sure the Docker service is running. On Linux, use sudo systemctl start docker.

Issue: Permission denied when running Docker commands.
Solution: Try running the command with sudo or add your user to the Docker group.

Practice Exercises

• Create a Dockerfile for a simple Node.js application and build an image from it.
• Run a MySQL container and connect to it using a MySQL client.
• Experiment with Docker Compose to run a multi-container application.

Remember, practice makes perfect! Don’t hesitate to experiment and try new things. You’ve got this! 💪

For more information, check out the official Docker documentation.