Docker Basics: Images, Containers, and Key Commands

• Docker is a container-based virtualization platform that runs and manages Linux applications as containers using process isolation technologies, allowing software to be packaged and distributed in units isolated from the environment.

• The advantage of Docker containers is that everything needed to run the software is wrapped in a complete file system, so the software always runs identically regardless of the environment it is executed in.

• Docker image
  • A file system containing everything needed to run an application.
  • Images are defined with a Dockerfile and built with the Docker CLI.
• Docker container
  • An instance of a Docker image, with its own file system and application runtime environment.
  • Containers are isolated but can share the host system’s resources.
• Docker registry
  • A repository used to store and share Docker images.
  • Docker Hub is the most widely used platform.
• Docker Compose
  • A tool for defining and running Docker applications.
  • Multiple containers are defined in a YAML file and the application can be started with a single command.
• Docker Swarm
  • A Docker clustering and orchestration tool that manages and deploys Docker containers across multiple hosts.
  • Swarm is used to scale services and ensure high availability.

docker command

Descriptions of frequently used docker commands

docker pull image_name

Pulls an image from Docker Hub or another Docker registry.

docker commit container image_name

Commits a running container as an image (turns the container into an image).

docker run --options

Used to create and run a container from a docker image. There are many options.

-d : run the container in the background

-v : share a directory between the host and the container

-e : set environment variables inside the container

–name : specify the name of the container to run

-it : run the container interactively

etc..

docker ps

Lists the containers running in the docker environment.

docker ps -a

Lists all containers in the docker environment.

docker image list

Shows the list of Docker images.

docker rm container_name

Deletes a Docker container.

docker rm image_name

Deletes a Docker image.

docker exec -it container_name /bin/bash

Opens an interactive bash shell inside a running Docker container.

docker attach container_name

Attaches to a running container and takes control of its terminal.

docker start container_name

docker stop container_name

Starts or stops a container.

Sharing the DISPLAY locally

xhost +local:

Conclusion

• Docker’s advantage is that development, test, and production environments can be kept consistent.
• Virtualized containers are lightweight and start quickly, so resources are used efficiently.
• Containers run identically anywhere, giving excellent portability.