Docker for Rails Developers: Build, Ship, and Run Your Applications Everywhere

225 Pages·2019·4.83 MB·English

by  Rob Isenberg

Early Praise for Docker for Rails Developers
With the avalanche of DevOps tools in use, this text has definitely cleared up the
mystery. I’ve been waiting for a Docker book aimed at Rails projects, and I’m now
convinced Docker is the way to go.
➤ Nigel Lowry
Company Director and Principal Consultant, Lemmata
Docker for Rails Developers is a wonderful book that allows you to jump in and
start converting your existing apps to run in containers. It is well written, easy
to follow, and makes you want to keep reading. I recommend this book for anyone
with a little Rails experience who wants to get a jump start on using Docker.
➤ Chris Johnson
Operations Manager, healthfinch
With this book at my side, I was able to help my team move our largest, highest-
revenue service into containers. This migration made disaster recovery much
faster and more reliable, and made it possible to open a data center in a whole
new market.
➤ Erin Dees
Lead Software Engineer, New Relic
This is much more than a how-to book, with the best technical writing I’ve seen
recently. Isenberg’s excellent guide provides clear and understandable explanations
of how to solve Rails-specific Docker DevOps issues. This is the kind of thing I
wish Docker had published a long time ago.
➤ David L. Bean, PhD
Director of Data Science, PayClip, Inc.
Docker for Rails Developers is more than just a fantastic resource for Ruby and
Rails developers looking to get up to speed with Docker. It’s a great, no-frills guide
for how to use the technology in practical, real-world situations, and I’d have no
hesitation in recommending this to Python or Node developers either. I’ve been
waiting since 2014 for a go-to book to hand to the Docker curious, and this might
just be it.
➤ Alexander Lynham
Owner, envoys.io
Docker for Rails Developers
Build, Ship, and Run Your Applications Everywhere
Rob Isenberg
The Pragmatic Bookshelf
Raleigh, North Carolina
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ISBN-13: 978-1-68050-273-2
Book version: P1.0—February 2019
Ruth. In hindsight, writing a book whilst hav-
ing a baby and renovating a house probably
wasn’t the best idea—who knew? Thank you
for your patience, love, and support. None of
this would have been possible without you.
Sammy. I couldn’t have imagined the joy and
love you’d bring into our life. Be kind, be
brave, and be willing to take risks in pursuit
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much.
Mum and Dad. Thank you for everything.

Contents
Acknowledgements . . . . . . . . . . . xi
Introduction . . . . . . . . . . . . xiii
Part I — Development
1. A Brave New World . . . . . . . . . . . 3
Installing Docker 3
Verifying Your Install 5
Before We Begin 6
Running a Ruby Script Without Ruby Installed 7
Generating a New Rails App Without Ruby Installed 10
Quick Recap 15
2. Running a Rails App in a Container . . . . . . . 17
How Do We Run Our Rails App? 17
Defining Our First Custom Image 18
Building Our Image 23
Running a Rails Server with Our Image 25
Reaching the App: Publishing Ports 26
Binding the Rails Server to IP Addresses 28
Quick Recap 29
3. Fine-Tuning Our Rails Image . . . . . . . . . 31
Naming and Versioning Our Image 31
A Default Command 33
Ignoring Unnecessary Files 34
The Image Build Cache 36
Caching Issue 1: Updating Packages 37
Caching Issue 2: Unnecessary Gem Installs 38
Contents • viii
The Finishing Touch 41
Quick Recap 42
4. Describing Our App Declaratively with Docker Compose . . 45
Getting Started with Compose 45
Launching Our App 47
Mounting a Local Volume 50
Starting and Stopping Services 51
Other Common Tasks 53
Quick Recap 56
5. Beyond the App: Adding Redis . . . . . . . . 59
Starting a Redis Server 60
Manually Connecting to the Redis Server 62
How Containers Can Talk to Each Other 63
Our Rails App Talking to Redis 64
Starting the Entire App with Docker Compose 67
Quick Recap 68
6. Adding a Database: Postgres . . . . . . . . . 71
Starting a Postgres Server 71
Connecting to Postgres from a Separate Container 74
Connecting Our Rails App to Postgres 75
Using the Database in Practice 80
Decoupling Data from the Container 81
Quick Recap 85
7. Playing Nice with JavaScript . . . . . . . . . 87
The JavaScript Front-End Options 87
Rails JavaScript Front End with Webpacker 88
Compiling Assets with Webpacker 90
A Hello World React App 92
Quick Recap 94
8. Testing in a Dockerized Environment . . . . . . 95
Setting Up RSpec 96
Our First Test 97
Setting Up Rails System Tests 99
Running Tests That Rely on JavaScript 101
Debugging 109
Quick Recap 110