Docker

2.1 Docker installation

# Check docker
docker version
sudo docker run hello-world

• On Linux
  • Docker client, Docker daemon and Container runs on the same Host
• On Window or MacOSX
  • Docker daemon cannot be run directly on Non-Linux platform natively because it user Linux specific Kernel feature
  • Need to run inside Docker-Machine
    • Install Docker Desktop

• Docker client –> docker commands, docker CLI
• Docker server –> dockerd(docker daemon)

2.1.1 Docker Engine vs Docker Desktop

Docker engine is the layer on which Docker runs. It’s a lightweight runtime and tooling that manages containers, images, builds, and more.

https://docs.docker.com/engine/install/ubuntu/

Docker Desktop provides GUI to manage containers, applications, and images directly from your machine. It includes Docker Engine along with additional features.

Docker Desktop on Linux runs a Virtual Machine (VM) which creates and uses a custom docker context, desktop-linux, on startup.

This means images and containers deployed on the Linux Docker Engine (before installation) are not available in Docker Desktop for Linux.

Commercial use of Docker Desktop in larger enterprises requires a paid subscription.

https://docs.docker.com/desktop/install/linux-install/

2.1.2 Try docker on Web

• Play with docker without Installation
  • A simple, interactive and fun playground to learn Docker

2.1.3 Docker Installation in Ubuntu

Uninstall old versions

# Uninstall- unofficial packages:
sudo apt-get remove docker docker-engine docker.io

for pkg in docker.io docker-doc docker-compose docker-compose-v2 podman-docker containerd runc; do sudo apt-get remove $pkg; done

Installation

# Set up Docker's apt repository.

sudo apt-get update
sudo apt-get install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

echo \
  "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
  $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

sudo apt-get update

# Install the Docker packages.
sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

# Verify installation
sudo docker run hello-world

2.1.4 Docker Installation in Windows

Install Docker Toolbox

• Deprecated –> Now Docker Desktop is used
• https://github.com/docker-archive/toolbox
• https://www.geeksforgeeks.org/docker-toolbox/

If you install Docker Toolbox on a Windows machine, the installer automatically installs Oracle Virtualbox to run the Docker virtual machine.

The Docker Toolbox installs everything you need to get started with Docker on Mac OS X and Windows. It includes the Docker client, Compose, Machine, Kitematic, and VirtualBox.

Install Docker Desktop

• Docker Desktop WSL 2 backend on Windows: https://docs.docker.com/desktop/wsl/
• Install Docker Desktop on Windows: https://docs.docker.com/desktop/windows/install/

Windows Subsystem for Linux (WSL) 2 is a full Linux kernel built by Microsoft, which lets Linux distributions run without managing virtual machines. With Docker Desktop running on WSL 2, users can leverage Linux workspaces and avoid maintaining both Linux and Windows build scripts. In addition, WSL 2 provides improvements to file system sharing and boot time.

# Check WSL version
wsl --status

# Change WSL version to WSL2
wsl --set-default-version 2

• Install Docker Desktop

# Check installation/version
docker -v

2.1.5 Docker Installation in Mac

• Install Docker Desktop

2.2 Post-installation steps for Linux

Manage Docker as a non-root user

Want to avoid typing sudo for docker command

# Create the docker group.
sudo groupadd docker

# Add your user to the docker group.
sudo usermod -aG docker $USER

# activate the changes to groups
newgrp docker

# Check
docker run hello-world

• Later

sudo usermod -aG docker ${USER} && su - ${USER} && id -nG
sudo usermod -a -G docker ${USER} 

Configure Docker to start on boot

• Automatically start Docker and Containerd on boot

sudo systemctl status containerd.service

# Enable
sudo systemctl enable docker.service
sudo systemctl enable containerd.service

# Disable
sudo systemctl disable docker.service
sudo systemctl disable containerd.service

Docker/Container Status

# Check docker status
sudo systemctl status docker

# Stop
sudo systemctl stop docker
sudo service docker stop

# Start
sudo service docker start

# Restart
sudo service docker restart
sudo systemctl restart docker.service

2.3 Containers vs Image

Docker Image (DI)

• DI are read only templates used to create containers.
• DI are created with the docker build command, either by us or by other docker users
• DI are composed of layers of other images.
• Stored in docker-registry(DockerHub)

Containers

A container is a runtime instance of an image build from one or more images. Run docker image, to make a docker container

Docker Hub

Docker-registry: A registry is where we store docker images, Inside a registry, images are stored in repositories.

Docker repository is a collection of different docker images with the same name, that have different tags, each tag usually represents a different version of the image.

Types of registry:

1. Own/local registry
2. Public registry (DockerHub)

docker login
# <username> & <password>

Client-Server Architecture

• Docker Life cycle

It runs natively on Linux systems and is made up of:

1. A Docker Daemon

• Also refer as –> Docker Engine or Docker Server
• It runs in the host computer.
• The Docker daemon is what actually executes commands sent to the Docker Client like building, running, and distributing your containers.

2. A Docker Client

• Command line interface (CLI) –> act as client
• It accepts commands from user, to communicate to daemon –> to execute commands
• Commands –> docker build, docker pull, docker run

3. Registry

• Repo for Docker Images

Commands-1(Basic)

version, info

Display Docker version and info

# docker version
docker --version
docker -v

# docker packages - version
docker version

docker info

run, start/stop/kill

• Run Docker image
• run = pull + create + start + attach

docker run <image_name>:<tag>

# TEST
docker run hello-world

# busybox --> is a lightweight Linux
docker run busybox
# pull + create + start + attach + EXITED

docker run httpd
# pull + create + start + attach

docker run -d httpd
# pull + create + start + do not attach

docker run ububtu
# pull + create + start + attach + EXITED

docker run -itd ububtu
# pull + create + start + attach

• start –> Run stopped/created container (status-UP/RUNNING)
• stop –> gives time to shutdown gracefully –> Recommended
• kill –> shutdown immediately –> Not Recommended

docker start/stop/kill <containerName/ID>
docker container stop <containerName/ID>

exec, -it, –rm

exec –> Execute command for the container. To use the docker exec command, you will need a running Docker container.

-it –-> Interactive, pass stdin (-i) as a tty, pass signals (-t)

–rm –-> Remove the container once it is stopped.

• NOTE: Always use -it with exec
  • Exception for minimal docker image like: busybox, hello-world

• -it can be used directly only for - minimal docker image

docker run -it busybox
# pull + create + start + attach

docker run -itd busybox ls

docker run -it --rm busybox

• For Other

# run docker in background
docker run -d busybox watch "date >> /var/log/date.log"

docker ps

docker exec -it 5dce543656c9 ls
docker exec -it 5dce543656c9 /bin/sh
docker exec -it 5dce543656c9 sh
exit

# stop
docker stop 8699be9f054d

inspect, attach, Map Port

• inspect - Return low-level information on Docker objects
• attach - Go inside container

docker inspect 8699be9f054d

docker run -it --rm busybox 
# CID - a07f1a4b716d

# detach
ctrl+p, ctrl+q

docker attach a07f1a4b716d

Map docker port to system port

docker run -d -p 81:80 httpd
# localhost:81

docker run -d -p 82:80 httpd
# localhost:82

ls, ps

• List all images

docker image ls
docker images

• List all running containers

docker ps
docker container ls

• List all containers, including stopped –> *

docker ps --all
docker container ls -a

Running an image relatedly will create multiple copy of the image with different container id and this may consume more memory in the system

docker run busybox ls     # <cid-1>
docker run busybox whoami # <cid-2>
docker run busybox ls     # <cid-3>

# Check copies of containers
docker ps --all

Remove stopped containers

# All
docker container prune

# Specific
docker rm <containerName/ID>

Remove unused Docker objects

# Remove dangling images
docker image prune

# This will remove all images without at least one container associated to them
docker image prune -a

# Prune everything --> prunes images, containers, and networks
docker system prune
docker system prune -a

Command-2

docker pause <containerName/ID>
docker unpause  <containerName/ID>
docker top <containerName/ID>
docker stats <containerName/ID>

docker history <imageName/ID>

docker images --help
docker images -f “dangling=false”
docker images -f “dangling=false” -q

docker rmi -f <id>

PUSH, PULL docker image

Push the image tp docker hub

# Login to docker hub
docker login

# Change name of the image, if not compatible to syntax
docker image tag <old_name:Version> <user_name>/<old_name>:<version>
docker image tag python-3.6.15 amritkr6/python-3.6.15:v1

# Push
docker push amritkr6/python-3.6.15:v1

Pull an image from hub –> pull

docker pull <image_name>
docker pull <image_name>:<tag>
docker pull hello-world