Docker

Put your application into containers

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Once upon a
time...
… in the land of infrastructures

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 Once upon a time...
Use case
Simple 3-Tiers application

‒ An HTTP server for your website

‒ A Java application for your API

‒ A PostgreSQL database for persistence

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 Once upon a time...
Multiple services / single server
Your application is getting complex… Company
‒ with multiple backend
■ with multiple languages
‒ with a lot of config
■ http servers, SSL certs, firewalls, LDAP, …
‒ … and harder to (re)deploy
‒ no process isolation
■ bad for security & resiliency*

*resilience: tolerance to faults 4

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 Once upon a time...
Multiple services / multiple servers
Your application is getting complex…
Company
‒ Put things in bare-metal servers!

PROS? CONS?

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 Once upon a time...
Multiple services / multiple servers
Your application is getting complex… Company
‒ Put things in bare-metal servers!

‒ Great performance
‒ Perfect process isolation

‒ Costly
‒ Harder to deploy and manage
‒ No automatic scaling
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 Once upon a time...
Multiple services / multiple VMs
Your application is getting complex… Company
‒ Put things in bare-metal servers!
VM 1 VM 2
‒ Put things in VMs*.

PROS?

VM 3

Your application is getting complex…

● Put things in bare-metal servers!
● *VM: Virtual
Put things in VMs*.Machine 7
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 Once upon a time...
Multiple services / multiple VMs
Your application is getting complex… Company
‒ Put things in bare-metal servers!
VM 1 VM 2
‒ Put things in VMs*.
‒ Everything in a single package
‒ Configure once, redeploy everywhere
‒ No Conflicting tools
■ ie: python + python3, JRE versions,... VM 3
‒ Great process isolation

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Containers
Why ?

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 Containers
Why ?
Your application is getting complex… Company

‒ Put things in bare-metal servers!

VM 1 VM 2
‒ Put things in VMs*.

CONS?
VM 3

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 Containers
Why ?
Your application is getting complex… Company

‒ Put things in bare-metal servers!

VM 1 VM 2
‒ Put things in VMs*.
‒ Setup & maintenance
‒ Performance overload
■ requires beefy hardware
■ no resource management VM 3
‒ Heavy to store and slow to start
‒ Hard to share
■ GIT ? FTP ?
■ need other solutions (ig: Vagrant, Terraform,
…)
● virtual machine 11
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We want something like
light virtual machines.

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Docker
containers, containers everywhere !

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 Docker
Containers
‒ Open source
‒ Docker != VM. Docker ≈ lightweight VM
■ Package application and its dependencies
■ Isolate processes
‒ One usage = One container
■ eg: front-end + back-end + 1 DB = 3 containers
‒ Build once, ship everywhere
■ One docker image for all environment
‒ Version Control
■ Versioned images

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 Docker
Containers vs VM
VM1 VM2

Clients :443 :5432

bin & libs bin & libs

Guest OS Guest OS

‒ Isolated processes: virtual HW virtual HW

■ Virtual Machines (RAM, CPU, (RAM, CPU,
￮ slow virtual hardware NIC, HDD, …) NIC, HDD, …)
￮ slow booting up guest OS
￮ lock host’s resources
Host OS

Host Hardware
(RAM, CPU, NIC, …)

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 Docker
Containers vs VM
Docker1 Docker2

Clients :443 :5432

bin & libs bin & libs

‒ Isolated processes: Docker engine

■ Virtual Machines
■ Containers
UNIX-based Host OS
￮ uses host hardware & software (fast)
￮ do not boot guest OS (fast) Kernel
￮ minimal virtualization overread (network, filesystem, …)

Host Hardware
(RAM, CPU, NIC, …)

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Take away

Docker rather than VMs ?

● runs processes right on host OS
■ no virtualization overread
■ fast
￮ start, stop, recreate containers in seconds
● emulated process isolation
● Dockerfile
■ Repeatable builds
■ can be versioned
● 1 single artifact, deployed everywhere
■ (binaries, libraries, conf, files …)

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Docker stuff
Images, containers, volumes, networks...

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 Docker
Images
Containers are made out of images
‒ image ≈ immutable, static
container
‒ one image = one usage
■ java + db + python = 3 images
■ reusable
■ minimal size
‒ built with Dockerfile

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 Docker
Dockerfile
‒ “makefile” recipe to create an # Base image

image FROM ubuntu:22.04

■ stack layers on top another image # Run a command in the container

# (eg: install a dependency)

RUN apt update && apt install sl layer 1

# Default program to run when container starts

ENTRYPOINT ["/usr/games/sl"] layer 2

# Default command/args to pass to command above

CMD [".", "-e"] layer 3

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 Docker
Dockerfile
from Dockerfile to image

# build docker image

docker build . -t my-image

latest
+ java:
+ conf
+ jar
+ ...

Dockerfile docker image

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 Docker
Containers
builds images, to create containers

latest
+ java: >$ docker build >$ docker run
+ conf
+ jar
+ ...

Dockerfile docker image docker container

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 Docker
Containers
‒ live, running copies of images

# run the latest nginx version in a container with name nginx

docker container run --name my-nginx nginx:latest

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Containers commands
# Run a nginx container with name my-nginx
docker container run \
--name my-nginx \ # with container name=my-nginx
-it \ # with interactive terminal
-d \ # daemon mode (not linked to a terminal)
nginx:1.15.8 # based on specific nginx 1.15.8 image

# Stop | kill (sends a SIGKILL) a running container

docker container {stop|kill} my-nginx

# Lists running containers | all containers

docker container ps [-a]

# Execute a command (bash) in a running container

docker container exec -it my-nginx bash

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 Docker # create a network
Networks docker network create -d bridge public-net

‒ “Containers are isolated” # run server

■ invisible from each other docker run -d \

‒ Networks: --name my-http \

--network=public-net \
■ connect containers
hashicorp/http-echo -text= "hello world"
together
■ one application = dozen of
# run client
containers in a network
docker run \
--name my-client \
--network=public-net \
-it \
-p 5678:5678 \
curlimages/curl my-http

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 Docker
Volumes
# bind-mount a volume
‒ “Containers are stateless:” docker run -d \
■ Keep no valuable data
--name my-nginx \
■ Can be destroyed or replaced,
-v "$(pwd)"/hostDir:/containerDir \
anytime
nginx
‒ Volumes
■ are a safe place on host
■ shared between containers
■ survive to container’s destruction

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 Docker
Volumes use if you want to share files between host and container

# bind-mount a volume
‒ Bind-Mount volumes docker run -d \
■ mount a host folder into the
--name my-nginx \
container
-v "$(pwd)"/hostDir:/containerDir \
■ are OS dependent
nginx
■ let the container add files that
are owned by root
use if you want files on a safe place, without the need of
accessing them

# bind-mount a volume
‒ Named volumes docker volume create my-volume
■ are managed by docker engine
■ can be on a remote machine docker run -d \
■ cannot be accessed directly by --name my-nginx \
host -v my-volume:/containerDir \
nginx

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Take away

‒ Start with an appropriate base image

■ as light as possible (eg: alpine is best)
‒ Reduce the number of layers
‒ One container = one concern
‒ No unnecessary packages installation (Text Editor …)
‒ Never use latest as a version
‒ RTFM
■ https://docs.docker.com/develop/dev-best-practices/#how-to-keep-your-images-small
■ https://docs.docker.com/engine/userguide/eng-image/dockerfile_best-practices
‒ use read-only volume if you do not need write access

# bind-mount a volume
docker run -d \
--name my-nginx \
-v "$(pwd)"/hostDir:/containerDir:ro \
nginx

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Docker universe
Docker-compose, Docker HUB & co

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 Docker universe
Docker compose
‒ Manage multiple containers # docker-compose.yml
together
■ build, run, build & run, start, stop version: "3"
‒ Declarative YAML Syntax services:
■ Services (= containers) myapp-web:
■ Networks image: "nginx:latest"
■ Volumes ports:
- "8080:80"
myapp-mysql:
image: "mysql:latest"

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 Docker universe
Docker HUB
‒ “github” for docker
■ public place to store docker images
‒ host docker images
■ images are already built
‒ official & unofficial images

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 Docker universe
Go Deeper
‒ Docker is a great tool but most of
the time production requires
■ Multi instances deployment
■ Vertical and / or Horizontal scaling
■ Fault tolerance on instance crashes
‒ Say Hello to : Containers
Orchestration
■ Deploy, manage and expose
containers on multiple instances

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 Contributors

Thank you.
‒ Nicolas THIERION <nthierion@takima.fr>
‒ Quentin BISSON <qbisson@takima.fr>
‒ Aurélien MORREAU <amorreau@takima.fr>

Lab: https://guide.master3.takima.io/docker-01
See also
Leave feedback: feedback form
‒ 01 - Devops
‒ 03 - Gitlab CI
‒ 04- Ansible (Bonus)

Contact formation@takima.fr
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 Références

● Why docker
● https://docs.docker.com/

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