Dockerizing Ruby Applications - The Best Practices

Dockerizing Ruby
Applications- The Best
Practices
Lauri Nevala, Co-Founder and Software Engineer

© 2015 Kontena, Inc.
What is Kontena?
Open Source container platform built
to maximize developer happiness.
Works on any cloud, easy to setup,
simple to use.

Quick Facts
650+GITHUB STARGAZERS
>100kNUMBER OF INSTALLS
FEATURED IN

All Batteries Included!
Built-In Image Registry
Sometimes projects can not use publicly
hosted container image registries like
DockerHub. Kontena comes with built-in
container image registry providing private
and secure solution.
Built-In VPN Access
All containers are run inside a virtual private
network by default. Nothing is exposed to
Internet unless explicitly defined. With
Kontena’s built-in VPN access developers
can securely access those resources.
Built-In Load Balancer
Kontena comes with built-in load balancer.
Based on Haproxy. It features fully
automatic, zero-downtime operation due to
deep integration with Kontena’s service
discovery and orchestration technology.
Aggregated Stats & Logs
Kontena provides real-time log and statistics
streams containers. The streams may be
grouped and aggregated to produce service
level streams. This allows easy viewing of
logs and statistics for your application CPU,
memory, disk and network usage.
User Management with Audit Trail
All events and actions performed through
Kontena CLI or APIs are logged into audit
trail. Combined with users and access
control, the audit trail support makes
Kontena a reliable and secure solution for
any enterprise deployments.
Built-In Secrets Management
When your application requires access to
APIs or databases, you'll often need to use
secrets such as passwords and access
tokens for authenticating the access.
Kontena Vault is a secure key/value storage
that can be used to manage secrets in
Kontena.

“Includes all that sh*it you don’t need to
implement by yourself”

Containers vs. VMs
INFRA
HOST
OS
APP
INFRA
HOST
OS
APP
INFRA
HOST
OS
APP
INFRA
HOST OS
HYPERVISOR
GUEST
OS
GUEST
OS
GUEST
OS
APP APP APP
INFRA
HOST OS
CONTAINER ENGINE
APP APP APP
Legacy Virtualization Containerization
Year 2014 

Docker Core Concepts
• Dockerfile
• Describes a Docker image
• Docker image
• “Compiled” version of the Dockerfile
• Docker container
• Running instance of the Docker image

Docker Image
• Packs up the application and environment required by the
application to run
• Consist of image layers
• Extends a base image

Ruby Base Image Strategies
• Official Ruby images
• ruby:version
• defacto image, has a large number of extremely common Debian packages
• ruby:onbuild
• really useful for "getting off the ground running”.
• it's not recommended for long-term usage within a project due to the lack of control
over when the ONBUILD triggers fire
• ruby:slim
• contains the minimal packages needed to run ruby
• ruby:alpine
• based on Alpine Linux. The main caveat to note is that it does use musl libc instead
of glibc and friends, so certain software might run into issues depending on the depth
of their libc requirements
• Build your own Ruby image
• Include only those libraries that are needed for your app

Sometimes size does matter

Ruby:2.3.1
729 MiB
Ruby:2.3.1-
slim
283 MiB Ruby:2.3.1-
alpine
125 MiB
Sizes of the Official
Ruby Images

Docker Containers – Best practices
• Run one process per container
• Twelve-Factor App FTW!
• Store config in the environment
• Treat backing services as attached resources
• Export services via port binding
• Treat logs as event streams
• Etc.
• Don’t rely on IP addresses

Dockerfile
FROM ruby:2.3.1-alpine
ADD Gemfile /app/
ADD Gemfile.lock /app/
RUN apk --update add --virtual build-dependencies ruby-dev build-base &&
gem install bundler --no-ri --no-rdoc &&
cd /app ; bundle install --without development test &&
apk del build-dependencies
ADD . /app
RUN chown -R nobody:nogroup /app
USER nobody
ENV RACK_ENV production
EXPOSE 9292
WORKDIR /app

Sending build context to Docker daemon 29.7 kB
Step 1 : FROM ruby:2.3.1-alpine
---> adae74697505
Step 2 : ADD Gemfile /app/
---> 81f926a9e4d6
Removing intermediate container 1000f93a8025
Step 3 : ADD Gemfile.lock /app/
---> ed3e4a1dfe0e
Removing intermediate container 5920c0c209e6
Step 4 : RUN apk --update add --virtual build-dependencies ruby-dev build-base && gem install bundler --no-ri --no-rdoc && cd /app ; bundle install -
-without development test && apk del build-dependencies
---> Running in 09029fc13d73
fetch http://dl-cdn.alpinelinux.org/alpine/v3.3/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.3/community/x86_64/APKINDEX.tar.gz
(1/23) Installing gmp (6.1.0-r0)
(2/23) Installing libgcc (5.3.0-r0)
(3/23) Installing libstdc++ (5.3.0-r0)
(4/23) Installing libgmpxx (6.1.0-r0)
(5/23) Installing gmp-dev (6.1.0-r0)
(6/23) Installing libedit (20150325.3.1-r3)
(7/23) Installing ruby-libs (2.2.4-r0)
(8/23) Installing ruby-dev (2.2.4-r0)
(9/23) Installing binutils-libs (2.25.1-r0)
(10/23) Installing binutils (2.25.1-r0)
(11/23) Installing isl (0.14.1-r0)
(12/23) Installing libgomp (5.3.0-r0)
(13/23) Installing libatomic (5.3.0-r0)
(14/23) Installing mpfr3 (3.1.2-r0)
(15/23) Installing mpc1 (1.0.3-r0)
(16/23) Installing gcc (5.3.0-r0)
(17/23) Installing make (4.1-r0)
lauri@kontena.io ~/helsinki-ruby-
brigade/todo$
docker build -t kontena/todo-example:latest .

(18/23) Installing musl-dev (1.1.12-r5)
(19/23) Installing libc-dev (0.7-r0)
(20/23) Installing fortify-headers (0.7-r0)
(21/23) Installing g++ (5.3.0-r0)
(22/23) Installing build-base (0.4-r1)
(23/23) Installing build-dependencies (0)
Executing busybox-1.24.1-r7.trigger
OK: 192 MiB in 55 packages
Successfully installed bundler-1.12.5
1 gem installed
Fetching gem metadata from https://rubygems.org/
Fetching version metadata from https://rubygems.org/
Installing i18n 0.7.0
Using json 1.8.3
Installing minitest 5.9.0
Installing thread_safe 0.3.5
Installing builder 3.2.2
Installing bson 4.1.1 with native extensions
Installing origin 2.2.0
Installing puma 3.4.0 with native extensions
Installing rack 1.5.2
Installing tilt 1.4.1
Using bundler 1.12.5
Installing tzinfo 1.2.2
Installing mongo 2.2.5
Installing rack-protection 1.5.3
Installing activesupport 4.2.6
Installing sinatra 1.4.5
Installing activemodel 4.2.6
Installing mongoid 5.1.3
Bundle complete! 3 Gemfile dependencies, 18 gems now installed.
Gems in the groups development and test were not installed.

Bundled gems are installed into /usr/local/bundle. Purging libgomp (5.3.0-r0)
Executing busybox-1.24.1-r7.trigger
OK: 23 MiB in 32 packages
---> 829379018bc7
Removing intermediate container 09029fc13d73
Step 5 : ADD . /app
---> 66705b32dc48
Removing intermediate container c7f73596c9ae
Step 6 : RUN chown -R nobody:nogroup /app

---> Running in be356cda2cd6
---> 0673c22b8d74
Removing intermediate container be356cda2cd6
Step 7 : USER nobody
---> Running in fd495cb3838a
---> 83cb7493aa53
Removing intermediate container fd495cb3838a
Step 8 : ENV RACK_ENV production
---> Running in edac524bbd44
---> e3b6c26647b2
Removing intermediate container edac524bbd44
Step 9 : EXPOSE 9292
---> Running in 4369855c3ab4
---> 3d82b78a2213
Removing intermediate container 4369855c3ab4
Step 10 : WORKDIR /app
---> Running in 6172a5c18269
---> e73df80077b5
Removing intermediate container 6172a5c18269
Successfully built e73df80077b5
lauri@kontena.io ~/helsinki-ruby-brigade/todo$

From Containers to Microservices
• Docker Compose
• Tool for defining and running multi-container Docker applications
• Services and their configurations are defined in YAML file(s)

docker-compose.yml
version: '2’
services:
web:
image: kontena/todo-example:latest
command: bundle exec puma -p 9292 -e production
environment:
- MONGODB_URI=mongodb://mongodb:27017/todo_production
ports:
- 9292:9292
links:
- mongodb:mongodb
mongodb:
image: mongo:3.2
command: mongod --smallfiles

Rolling to Production
• How big this app will be? How many users it will serve?
• Do you want your application to be infrastructure agnostic or
lean heavily on some cloud provider?
• How to run databases or save other persistent data?
• How to scale the application and handle load balancing?
• How do you pass sensitive data to your application and where
to store that data?
• How the application can be deployed and updated with zero
down-time?

kontena.yml
version: '2’
services:
mongodb: image: mongo:3.2
instances: 3
stateful: true
command: --replSet kontena –smallfiles
hooks:
post_start:
- cmd: sleep 10
name: sleep
instances: 1
oneshot: true
- cmd: mongo --eval "printjson(rs.initiate());”
name: rs_initiate
instances: 1
oneshot: true
- cmd: mongo --eval "printjson(rs.add('%{project}-mongodb-2'))”
name: rs_add2
instances: 1
oneshot: true
- cmd: mongo --eval "printjson(rs.add('%{project}-mongodb-3'))”
name: rs_add3
instances: 1
oneshot: true

app:
image: kontena/todo-example:latest
links:
- mongodb:mongodb
- loadbalancer
environment:
- MONGODB_URI=mongodb://%{project}-mongodb-1.kontena.local:27017,%{project}-mongodb-
2.kontena.local:27017,%{project}-mongodb-3.kontena.local:27017/todo_production
- KONTENA_LB_VIRTUAL_PATH=/
- KONTENA_LB_INTERNAL_PORT=9292
command: bundle exec puma -p 9292 -e production
loadbalancer:
image: kontena/lb:latest
deploy:
strategy: daemon
ports:
- 80:80

Deploying Application
brigade/todo$
kontena app deploy

Scaling Application
brigade/todo$
kontena app scale app 10

Resources
• Todo Example: https://github.com/kontena/helsinki-meetup-
hackathon
• Getting started: http://www.kontena.io
• GitHub: https://github.com/kontena/kontena
• Gitter: https://gitter.im/kontena/kontena
• Kontena Meetup: http://www.meetup.com/Kontena-Helsinki/

We are hiring!
kontena.io/jobs

Dockerizing Ruby Applications - The Best Practices

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