This article is meant to give a brief understanding of docker, it's components and use.
Docker
Docker is a software platform that simplifies the process of building, running, managing and distributing applications.
A Docker container is a loosely isolated environment running within a host machine’s kernel that allows us to run application-specific code along with it's dependencies.
Docker runs on top of the original host machine kernel.
The Kernel is the key program or software at the core an operating system with complete control of a computer or machine.
Docker Engine is an open source containerization technology for building and containerizing your applications and it consists of :-
- Docker Server or Docker daemon
- Docker Engine Application Program Interface (API)
- Docker Command Line Interface (CLI)
The diagram below explains their relationships.
How are containers created?
In programming terms: Docker containers can be described as objects that are created by a class in docker called Docker images.
A Docker Image is an executable package that contains a read-only template with set of instructions used to build a container. When these instructions are executed, it creates a Docker container. It can be compared to a snapshot used in a Virtual machine (VM) environment.
These instructions defines all what the container needs, this includes the container code, libraries, environment variables, configuration files, and more. Hence, a docker container can also be thought of as an instance of the set of instructions defined in a docker image running on a host machine.
It is also important to understand the relationship between a docker image and a docker container. It is not always a one to one relationship. It can be one to one or one to many, that is, many docker containers can be created from one docker image.
Let's create a docker container
- Install Docker desktop here
- Choose your OS on the left menu and follow the installation instruction
Quick getting started docker commands
# Search the docker hub for available ubuntu images
docker search ubuntu
# Create a new container base on the ubuntu image
docker create -it --name=fooo ubuntu bash
# List of started containers
docker container ls
# List created containers
docker container ls -a
# Start a created container
docker start fooo
# Start a interactive mode (-it) on the container
docker attach fooo
# Run a command in a new container
docker run --name=bar -it ubuntu bash
# Exit interactive mode
Ctl q+p
# Check container history
docker logs fooo
# Stop container
docker stop fooo
# Remove container
docker rm fooo
How to create docker containers fooo & bar from a ubuntu image
Desktop view of docker containers fooo and bar
Dockerfile
A Dockerfile outlines instructions for how an image will create a container. It is a text document that contains all the commands a user could call on the command line to assemble an image.
As always, I look forward to getting your thoughts on this article. Please feel free to leave a comment!
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