docker-sample

Diffrent methods of image creation:

1. Create an image from Scratch
2. Create an image from a Dockerfile
3. Create an image from a Container

Creating a Docker Image FROM Scratch

Building Docker images FROM scratch means starting from an empty base, without any preinstalled OS, ensuring lightweight, secure, and fully controlled containerization.

Why use FROM scratch?

• Minimal size
• Enhanced security
• Full control over dependencies

Example: Ultra-Lightweight Docker Image

FROM scratch  
COPY hello /  
CMD ["/hello"]

Dockerfile: The Preferred Method for Building a Docker Image

A Dockerfile is a script that defines step by step how to build a Docker image in an automated, efficient, and reproducible way. It acts as a recipe, ensuring consistency across deployments.

Building an Image: docker build

The essential command to create a Docker image:

docker build -t image_name path

1. Define the base image

FROM ubuntu:20.04

2. Set up the environment

LABEL maintainer="Jrad Mariem"
ENV APP_ENV=production
WORKDIR /app

3. Define the startup behaviour

• The CMD command is the default command that will be executed but if an argument is entered when running the container it would ignore the CMD Statement
• The Entypoint is a base command which prioritary comparing it with CMD .

Note

ENTRYPOINT vs. --entrypoint in Docker

• ENTRYPOINT (Dockerfile) sets a fixed command that runs by default.

  ENTRYPOINT ["ping", "-c", "4"]

  Running docker run my-image google.com executes: ping -c 4 google.com.
• --entrypoint (CLI) temporarily overrides ENTRYPOINT.

  docker run --entrypoint ls my-image

  Runs ls instead of ping.
• Use ENTRYPOINT for default behavior, --entrypoint for runtime overrides.

ENTRYPOINT ["echo"]

4. Run commands during build which creates a temporary container and executes the command and from it an image will be created

RUN apt-get update && apt-get install -y python3

Create a Docker Image from a Container

Use docker commit to save a container’s current state as a new image.

Syntax

docker commit [container_id] [image_name:tag]