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Docs: https://docs.docker.com/

Gist from Brad: https://gist.github.com/bradtraversy/89fad226dc058a41b596d586022a9bd3

Beginner Tutorial from Mosh: https://youtu.be/pTFZFxd4hOI

very good ELI5: https://www.reddit.com/r/AskComputerScience/comments/9xktwl/eli5_please_what_is_docker/

What is Docker?

  • like a virtual machine but structured differently to save RAM and CPU
  • Docker is a platform for building, running and shipping applications in a consistent manner, so if your application works on your developing machine, it can run and function the same way on other machines.

What is a Container

  • A Container is an isolated environment for running an application.
  • allows running multiple apps in isolation
  • are lightweight
  • use / share the OS of the host (every OS needs to be licensed, patched and monitored)
  • start quickly
  • need less hardware resources

What is a Virtual Machine?

  • A virtual machine is an abstract of a machine (or physical hardware).
  • For this we need a Hypervisor: a tool to create and manage virtual machines.
    • Examples are VirtualBox, VMware (which are both cross-platform (running on Mac, Linux and Windows)) and Hyper-v (Windows only)
  • Problems
    • each VM needs a full-blown OS (that needs to be licensed, patched and monitored)
    • slow to start (because entire OS has to be loaded)
    • resource intensive (CPU, Memory, Disk Space)

Docker Architecture

  • a client component talks to a server component via Restful API
  • the server component is here called Docker Engine
  • technically a container is a process, but a special kind of process with its own file system (which is provided by the image)
  • on a Linux machine we can run Linux containers
  • on a Windows machine we can now both run Windows and Linux containers, because since Windows10 they added a custom built Linux kernel
  • Docker on Mac uses a lightweight VM to run Linux containers
    • Mac doesn't have native support for continuous applications

What is a Dockerfile?

  • A dockerfile is a plaintext file that includes instructions that docker uses to package up this application into an image. This image contains everything our application needs to run.

What is an Image?

An image contains everything an application needs to run.

  • a cut-down OS
  • a runtime environment (eg Node)
  • application files
  • third-party libraries
  • environment variables

getting info

docker version docker info

Show all Containers / Prozesse:

docker ps // show all (running) processes

  • show all processes, including stopped ones: docker ps -a // show (-a) all (ps) processes

show only running containers:

docker container ls

Workflow after Setup:

  1. In empty folder create 'docker-compose.yml'

to run, start your docker containers:

docker-compose up -d (use docker-compose up without the -d to see what is happening (and know when it has finished))

to stop thus created docker containers:

docker-compose down

to list thus created containers even when they are down:

docker-compose ps -a

Example for docker-compose.yml:

version: '3.7'
services:
  ghost:
    image: ghost:latest
    restart: always
    depends_on:
      - db
    environment:
      url: http://localhost:3001
      database__client: mysql
      database__connection__host: db
      database__connection__user: root
      database__connection__password: MyStrongPassword
      database__connection__database: ghost
    ports:
      - 3001:2368
    volumes:
      - ./content:/var/lib/ghost/content
  db:
    image: mysql:5.7
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: MyStrongPassword

Docker is like a virtual machine but structured differently to save RAM and CPU.

initiate and run a docker container:

(Create instance from image) Beispiel: docker run -d --name some-ghost -e url=http://localhost:3001 -p 3001:2368 ghost Übersetzt: starte docker, (-d for 'detached') lass es im Hintergrund laufen, (--name) nenne es 'some-ghost', (-e) set environment variable: url=...., (-p) Portweiterleitung auf 3001 (von 2368), aus dem image 'ghost'

show all (running) docker container:

docker ps -a

stop docker container:

docker stop example-container-name

delete all non-active container and images:

docker system prune -af

ghost at docker:

https://hub.docker.com/_/ghost/

list all commands

docker and docker run --help

Docker Installation

(nach brew update): brew install --cask docker

download image:

you do it automatically when you start a container: docker run -d --name some-ghost -e url=http://localhost:3001 -p 3001:2368 ghost // last part calls the respective image down from docker hub

or you can do it directly: docker pull nginx

delete image

docker image rm exampleID // instead of exampleID use the first 3 digits of the image ID. To get the image ID: list all images (see below)

list all images

docker images or docker image ls

remove container

docker container rm example /instead of example use the first 3 digits from the containers ID

to see all containers run: docker container ls -a