Dockerfile, Images & Containers and Dockerhub

What is Dockerfile?

The Dockerfile contains instructions for generating a Docker image. Dockerfile will define the processes to quickly produce an image. It is a simple text file with a set of commands or instructions

What is Docker Image?

An artifact with several layers and a lightweight, compact stand-alone executable package that contains all of the components required to run a piece of software.

Docker Container: It is a running instance of a Docker Image as they hold the entire package needed to run the application. So, these are basically the ready applications created from Docker Images which is the ultimate utility of Docker.

Docker Hub is an online platform that acts as a central repository where developers can store, share, and retrieve Docker images. In simple terms, it's like a giant library or app store for pre-packaged software environments.

In lay man terms

1. Dockerfile

Imagine a Dockerfile as a script for a play. This script contains detailed instructions on everything that needs to happen in the play. It tells you what props you need, which actors are required, how the stage should be set up, and what each actor should do and say. In Docker terms, a Dockerfile is similar; it includes a list of commands and settings used by Docker to build an image. It tells Docker what base environment to use, what files to include, and what commands to run when setting up that environment.

2. Docker Image

A Docker image can be thought of as a DVD of the play. This DVD is a static, final copy of the play as directed and recorded. It contains all the elements of the play—actors' performances, stage settings, backgrounds, sounds—everything combined into a single package that can be played on any compatible DVD player. Similarly, a Docker image is a portable and immutable snapshot of the environment set by the Dockerfile, which includes everything needed to run an application.

3. Docker Container

Now, think of a Docker container as a performance of the play in front of an audience. Each time the DVD is played (the image is run), it's like putting on a new live performance of the play. The DVD ensures that no matter where or when the play is performed, everything happens exactly as it was recorded. Each performance can be slightly tailored to the audience (say by interacting with them differently), but the core of the play remains unchanged. In Docker, when you run an image, it creates a container, which is an instance of that image running as a separate process. You can run many containers from the same image, just like you can have many performances from the same DVD.

4. Docker Hub: Think of Docker Hub as a large DVD store or a library where DVDs of various plays (Docker images) are stored. Just like you can go to a DVD store to pick up a copy of your favorite movie or a new release, developers can go to Docker Hub to pull (download) Docker images they need to deploy applications.

Summary

In this analogy:

• The Dockerfile is like a play script, detailing how to set everything up.
• The Docker image is like a DVD, a static and complete copy of the play.
• The Docker container is like a performance of the play, bringing the script to life each time it's run.

This analogy helps illustrate how Docker packages applications (the play) into a complete and reproducible format (the DVD) that can be run consistently in various environments (the performances).