Docker Overview: A Comprehensive Guide

Welcome to our comprehensive guide on Docker! This article aims to provide you with an easy-to-follow overview of everything you need to know about Docker, from creating Dockerfiles to managing containers. Whether you’re a beginner or looking for a quick refresher, this cheat sheet will help you get started and navigate the basics of containerisation.

What is Docker?

Docker is a platform that allows developers to automate the deployment, scaling, and management of applications inside lightweight, portable containers. Containers are isolated environments that package software with all its dependencies so it can run reliably across different computing environments.

Key Concepts

• Dockerfile: A text file containing instructions for building a Docker image.
• Image: A read-only template used to build Docker containers.
• Container: A running instance of an image, where your application runs.

How Do You Create a Dockerfile?

Creating a Dockerfile is the first step in using Docker. Follow these steps:

1. 1. Create and Open Dockerfile:

$ touch Dockerfile
$ code Dockerfile  # Use any text editor you prefer

1. 1. Define the Base Image:

Example:

Dockerfile
FROM node:18-alpine

This command sets `node:18-alpine` as the base image, which provides Node.js and a lightweight Linux distribution to reduce image size.

1. 1. Set Working Directory:

Example:

Dockerfile
WORKDIR /app

1. 1. Copy Application Files:

Dockerfile
COPY package*.json ./

1. 1. Install Dependencies and Build Application:

Dockerfile
RUN npm install
# Additional commands to build the application if necessary

1. 1. Expose Ports:

Dockerfile
EXPOSE 3000

1. 1. Define Entry Point or Command to Run the Application:

Dockerfile
CMD ["npm", "start"]

How Do You Build a Docker Image?

1. 1. Build an Image from Dockerfile:

Example:

$ docker build -t <image-name>:<tag> .

This command builds the Docker image based on instructions in `Dockerfile` and tags it.

1. 1. Tagging an Image:

How Do You Run Containers?

1. 1. Run a Container:

$ docker run <image-name>

1. 1. Run in Background (Detached Mode):

$ docker run --detach <image-name>

1. 1. List All Running Containers:

Example:

$ docker container ls  # or simply $ docker ps

1. 1. List All Containers (Running and Stopped):

$ docker container ls --all  # or $ docker ps -a

Managing Volumes

1. 1. Using a Named Volume:

$ docker run --volume <volume-name>:/path/in/container <image-name>

1. 1. Mounting Host Directory as Volume:

$ docker run --volume /path/on/host:/path/in/container <image-name>

1. 1. List All Volumes:

$ docker volume ls

Conclusion

This guide provides a brief overview of Docker and how to create, build, and manage Docker containers using a Dockerfile. For more advanced usage and best practices, consider exploring the official Docker documentation.