An introduction to Docker (Docker.io). Just a brief overview that describes a little of what Docker has to offer. The talk was hosted at kWantera HQ in Pittsburgh PA.
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Docker 101
1. Docker 101
An Introduction to Containerizing Apps
Benjamin Schmidt
kWantera.com CTO
2. Agenda
● What is Docker?
● Using Docker
● What can you do with Docker?
● Examples
● Tech that extends Docker
3. 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”
4. What is Docker?
“open platform … to build, ship and run
distributed applications”
Linux virtualization made easy (and light-weight)
5. 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
6. 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
7. 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
9. 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
10. Representation
Some inefficiencies pop-up
● Architecture duplication
● Setting up “fully systems”
=> Leads to resource waste
image source: docker.io
HEAVY copying &
redundancy
Potentially
redundant
11. 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
12. Terminology
● Container
o Runs your code using a specified environment
(Image) and the command you wish to execute in
that environment
● Image
o An environment complete with the type of OS and
any setup instructions for generating that
environment
13. 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
14. At this point...
● I want to give a flavor for Docker usage
without all the details
o See the Docs for extensive coverage
o This is just a 101 course :)
15. Let’s start a docker container...
$ sudo docker run ubuntu:14.04 /bin/echo ‘Hello World’
Hello World
16. Let’s start a docker container...
Accesses LXC
under the hood
(needs root)
The type of
Image
Convert from
Image to
Container
The command to
run in that image
type
$ sudo docker run ubuntu:14.04 /bin/echo ‘Hello World’
Hello World
17. 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
18. 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
19. 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)
20. 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
21. 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
22. Bind ports inside container to host...
$ sudo docker run -d -p 5000:5000 ubuntu python myserver.py
-p = port mapping.
(lower case)
Inside:Outside
23. Dockerfile
Create 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
24. Things to be Aware of...
● Containers run in their own environment
o 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
25. Things to be Aware of...
● Images are stored with a VCS-ish
o 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 Hub
o 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
26. Things to be Aware of...
● Resource limits
o Can set CPU and RAM limits
● Networking
o Docker creates an elaborate networking
infrastructure via clever use of /etc/hosts
o Do not modify /etc/hosts!! or do so at peril
27. Neat tech out there today...
Docker swarm:
https://github.com/docker/swarm
CoreOS Rocket:
https://github.com/coreos/rocket
