A brief introduction to containerization, Docker, and getting started with your first containerized Rails application. Source code can be found at https://github.com/rheinwein/rails-demo-apps

1. Building Rails
Applications with
Docker
Laura Frank @rhein_wein
Software Engineer @codeship

2. Today’s Agenda
• An introduction to containers: what are they, and what
makes them different from virtual machines?
• The Docker ecosystem
• Working with Docker on a Rails project
2

3. An Introduction to
Containerization

5. Docker != containers

6. Docker manages containers
• Builds images to run as containers
• Can manage entire applications with docker-compose
• Provision machines with docker-machine
6

7. A container is a virtualization layer
— sort of like a VM — but with
some fundamental differences

8. Containers
• Run in a self-contained execution environment
• Share the kernel of host system
• Are isolated from other containers
• Have fast boot times & low overhead
8

9. infrastructure
host OS
hypervisor
$
guest OS
libraries
service 0
$ guest OS $ guest OS
libraries
service 2
libraries
service 1

10. libraries librarieslibraries
infrastructure
host OS
service 0 service 2service 1

11. host OS
libraries librarieslibraries
infrastructure
container runtime engine
service 0 service 2service 1

12. Getting started with containers may
initially seem more complex…

13. …But they greatly reduce the
amount of time and space needed
to run your application

14. Spend less time provisioning,
rebooting, and fighting with
dependencies, and more time building
what you want.
TL;DR

15. The Docker Ecosystem

16. Build Ship Run

17. Docker Images

18. Are images containers?
No… an image is like a class, and a container is an
instance of that class

19. The Docker Hub
19

20. • ~15,000 images that you can pull down and use in your
own projects
• Also includes additional features like webhooks, build
triggers, authentication, and private repositories
• Use either the web GUI or the CLI — familiar workflow
of login, push, pull, search, etc.
The Docker Hub

21. Different Types of Images
• Service: self-contained images that provide a self-
contained service out-of-the-box. Postgres, MySQL.
• Project Base: intended to serve as a base for your own
project; do not directly provide a service. Ruby, golang.
• Official Images: maintained by the organization/
company themselves (i.e. the official Rails image)

22. • Build them yourself by creating a Dockerfile
• docker
build
-­‐t
image_name
.
#
don’t
forget
the
dot!
• run docker
images
to see all of the images you’ve
downloaded or built
Your Own Docker Images

23. A Rails Dockerfile
FROM rails:4.2.4
MAINTAINER Laura Frank <laura@codeship.com>
RUN mkdir -p /var/app
COPY . /var/app
WORKDIR /var/app
RUN bundle install
CMD rails s -b 0.0.0.0
set versions here

24. Use the Docker Hub to find and
store images to use in your project.
Use Docker Compose to build it.

25. Docker Compose
25

26. Building Your First Rails
App with Docker

27. Installing Docker
• The old way: boot2docker
• The new way: Docker Toolbox
• Docker Client, Machine, Engine, Compose (on a Mac),
Kitematic, and Virtual Box
• You can migrate your boot2docker VM to a Docker
Machine machine — check the docs

28. Installing Docker
🐳 docker.com/toolbox

29. Development Goals
Run a Rails app in a container, so that a developer can:
• view the app running in the browser
• edit files in a local environment and see the changes
• run rake tasks like migrations
• see log output

30. Remember This?
FROM rails:4.2.4
MAINTAINER Laura Frank <laura@codeship.com>
RUN mkdir -p /var/app
COPY Gemfile /var/app/Gemfile
WORKDIR /var/app
RUN bundle install
CMD rails s -b 0.0.0.0

32. 🚉 🐘
A Multi-­‐Container Rails App
Rails App Postgres
❤

33. How can I get containerized services to
communicate with one another?container linking, environment variables…
and of course, a little config sugar

34. Docker Compose makes this easy.

35. db:
image:
postgres
web:
build:
.
command:
bundle
exec
rails
s
-­‐p
3000
-­‐b
'0.0.0.0'
volumes:
-­‐
.:/var/app
ports:
-­‐
'3333:3000'
links:
-­‐
db
docker-­‐compose.yml

36. development:
&default
adapter:
postgresql
encoding:
unicode
database:
postgres
pool:
5
username:
postgres
password:
host:
db
config/database.yml

38. Ship It
A simple CI/CD workflow would include
• running tests
• building a new Docker image
• pushing that image to a registry
• firing up containers with the new image

39. #alwayskeepshipping

40. thanks!