docker 101

Docker 101

An Introduction to Containerizing Apps

Benjamin Schmidt

kWantera.com CTO

Agenda

● What is Docker?

● Using Docker

● What can you do with Docker?

● Examples

● Tech that extends Docker

Talk’s Purpose

● While simple, Docker is expansive in it’s

capabilities

● I’d like to cover enough so people can

understand the concepts

● I leave it to the docs and SO for becoming

“experts”

What is Docker?

“open platform … to build, ship and run

distributed applications”

Linux virtualization made easy (and light-

weight)

A Container For Your App

● You’ve got code

● Docker is a self-contained, customizable

linux environment to run that code

● It is a virtual machine without the full OS

Origins (-ish)

● Linux containers (LXC) :: sort of like chroot

● Create a kernel separated environment for

security purposes

● Since it’s part of kernel = does not require a

full OS

● Can run multiple containers on same system

● Sprinkle in resource constraints

● Add a dash of environment scripting

Representation

You have an “App” you want

to run:● Mongo server

● HTTP server

● Long-running script

● An ad-hoc backup script

image source: docker.io

Representation

Traditionally you run it on a

“full server”

image source: docker.io

The physical

hardware

Required

libraries

Representation

Virtualization solved the

multiple-app / library

problem● Still a single physical hardware server

image source: docker.io

Use Virtualization to

mirror the “physical”

hardware at OS level

Representation

Some inefficiencies pop-up● Architecture duplication

● Setting up “fully systems”

=> Leads to resource waste

image source: docker.io

HEAVY copying &

redundancy

Potentially

redundant

Representation

Docker Solution● There is only one running “full OS”

o You use a dedicated portion of kernel

resources

● Much lighter weight leads to:

o Easily cloneable containers

o Sharing system libraries versus program

libraries (i.e. a portion of the host kernel)

image source: docker.io

Terminology

● Containero Runs your code using a specified environment

(Image) and the command you wish to execute in

that environment

● Imageo An environment complete with the type of OS and

any setup instructions for generating that

environment

Using Docker

● Docker has a pretty simple command line

API*o run: converts images and commands into containers

o start/stop: starts or stops containers

o ps: inspect the available containers and their status

o images: list all available images (locally

downloaded)

o build: builds image (e.x from a Dockerfile)

*Other commands exist for more fine-grained control and inspection

At this point...

● I want to give a flavor for Docker usage

without all the detailso See the Docs for extensive coverage

o This is just a 101 course :)

Let’s start a docker container...

$ sudo docker run ubuntu:14.04 /bin/echo ‘Hello World’

Hello World

Let’s start a docker container...

$ sudo docker run ubuntu:14.04 /bin/echo ‘Hello World’

Hello World

Accesses LXC

under the hood

(needs root)

Convert from

Image to

Container

The type of

ImageThe command to

run in that image

type

And if you wanted to test in multiple

OS’s...$ sudo docker run ubuntu:14.04 /bin/echo ‘Hello World’

Hello World

$ sudo docker run ubuntu /bin/echo ‘Hello World’

Hello World

$ sudo docker run centos /bin/echo ‘Hello World’

Hello World

$ sudo docker run debian /bin/echo ‘Hello World’

Hello World

A few notes

● Program printed to STDOUT (the console)

● If you run `sudo docker ps` you won’t see

any currently running containers (it stopped)

● Running `sudo docker ps -a` will show a

stopped container

And if you want an interactive shell...

$ sudo docker run -t -i ubuntu:14.04 /bin/bash

root@ae23f43: |

-t = pseudo-tty

terminal-i = interactive (STDIN is

piped into process)

And if you want an interactive shell...

$ sudo docker run -t -i ubuntu:14.04 /bin/bash

root@ae23f43: |

And to know you’re not in a full OS, try

`top`... only two processes

And throw a process into

background...

$ sudo docker run -d ubuntu /bin/sh -c "while true; do echo hello world; sleep 1;

done"

1e5535038e285177d5214659a068137486f96ee5c2e85a4ac52dc83f2ebe4147

-d = daemonize

leaving off :14.04 provides

the “latest” version

Returns the

container ID

Bind ports inside container to host...

$ sudo docker run -d -p 5000:5000 ubuntu python myserver.py

-p = port mapping.

(lower case)

Inside:Outside

DockerfileCreate Images

# Put this in a file called Dockerfile

FROM ubuntu

MAINTAINER Ben Schmidt <ben@example.com>

RUN apt-get update

$ cd ~/myserver

$ sudo docker build -t=”myimage” .

$ sudo docker run -i -it myimage /bin/bash

A Dockerfile in ~/myimage/

-t = Set the name of the

image

Things to be Aware of...

● Containers run in their own environmento Files, ports, and host data must be “mapped” to the

container

o EXPOSE: exposes ports to host

o ADD: copies local host files into container

● Volumes allow exposure of host OS

filesystem to containers

o Can get very tricky! But allows shared storage and

even containers that act as storage only

Things to be Aware of...

● Images are stored with a VCS-isho Each line in a Dockerfile creates a new image

o FROM command allows stacking of images

o Can create parent-child relationships

o sudo docker commit or pull

● Docker Hubo Store your images in the cloud

o This is default how we access many of the common

images (ubuntu, centos etc.)

o Can also create your own private repository

Things to be Aware of...

● Resource limitso Can set CPU and RAM limits

● Networkingo Docker creates an elaborate networking

infrastructure via clever use of /etc/hosts

o Do not modify /etc/hosts!! or do so at peril

Neat tech out there today...

Docker swarm:

https://github.com/docker/swarm

CoreOS Rocket:

https://github.com/coreos/rocket

Thanks!!

Contact:

Ben Schmidt

kwantera.com