Using Docker for your Rails Development Environment

https://trbmeetup.doorkeeper.jp/events/88667

Docker is a tool designed to make it easier to create, deploy, and run applications by using containers. While there's a lot of information about using Docker for production Rails apps, I have been using it in development as well. Docker brings a lot of advantages for web application development, but it also creates some problems.

In this talk, I am going to share the benefits of using Docker, how to create a development environment with it, and how I have dealt with some of the challenges I've encountered.

Transcript

1. Using Docker for your Rails
   Development Environment
   2019/04/03 Tokyo Rubyist Meetup at PIXTA, Inc.
   

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2. Hi there
   ● Gentaro Terada (@hibariya)
   ● Works at ESM, Inc.
   ● A college student (engineering)
   ● Likes Ruby, Internet, and Programming
   ● https://hibariya.org
   

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3. Today we will talk about:
   ● Why/How to use Docker
   ● Problems/questions I faced
   

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4. Why To Use Docker
   

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5. What is Docker
   With Docker, we can:
   ● Create/run containers
   ● Create/share container images (kind of snapshots)
   

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6. Container is lighter
   Container vs. Virtual Machine
   https://www.docker.com/resources/what-container
   

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7. Why To Use Docker
   Docker makes it much easier:
   ● Build once, run anywhere
   ● Less “It works on my machine”
   ○ The same condition (Runtimes, Libraries, Server Applications, and so on)
   ● Re-creating environments easily/quickly
   ● Various environment can live together on the same
   host machine
   

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8. How To Use Docker
   

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9. The First Step
   A development environment for a small Rails application:
   1. Create a Dockerfile to build containers
   2. Create a docker-compose.yml to organize containers
   

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10. Dockerfile for a Rails app
    

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11. Creating a new Rails app
    On the host:
    $ docker build -f Dockerfile -t rails-docker-example .
    $ docker container run -it --rm \
    --volume=$(pwd):/work --workdir=/work \
    rails-docker-example bash
    On the container:
    # gem install rails --no-document
    # rails new example --database=postgresql --skip-bundle …
    

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12. docker-compose.yml to Organize
    

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13. Invoke the app
    $ docker-compose run --rm rails bin/setup
    $ docker-compose up
    

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14. Running a command inside a container
    Use a running container:
    $ docker-compose exec rails bin/rails c
    Create and run a new container:
    $ docker-compose run --rm rails bin/rails c
    

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15. For more details
    https://github.com/esminc/rails-docker-examples
    ● Example Rails app + PostgreSQL + Webpacker
    ● Configurations for Docker Compose
    ● Configurations for Kubernetes (w/ GKE)
    

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16. Problems I Faced
    

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17. Problems I Faced
    ● Testing with browsers
    ● Dockerfile doesn’t ensure the same image
    ● Too large images
    ● Generated files are owned by root
    ● Long / complicated commands
    ● Could not we use K8s for development?
    

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18. Testing with Browsers
    

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19. How to run browser testing?
    ● Plan A: Run a Selenium container and use it
    remotely (I recommend)
    ○ Easy debugging; Can view/inspect running browser via VNC
    ○ Does not add another dependency to the Rails container
    ● Plan B: Install a browser on the Rails container and use
    it in headless mode
    ○ Less custom settings (probably)
    ○ Needs browser installation on the Rails container
    

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20. docker-compose.yml
    test/application_system_test_case.rb
    

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21. Interactive Debugging with VNC
    Stop w/ a breakpoint, connect to localhost:5900 w/ VNC
    

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22. Dockerfile Doesn’t Ensure the Same Image
    

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23. Dockerfile doesn't ensure the same image
    ● Updates on base image
    ● Repository changes for package management system
    ○ e.g., EPEL-5 repository EOL (March 2017)
    ○ So the following Dockerfile does not work anymore
    

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24. Share the image
    

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25. Too Large Images
    

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26. Rails application images tend to be large
    We could:
    ● Use smaller base image
    ● Install only mandatory packages
    ● Remove caches at the same time
    ● Use multi-stage builds for assets compilation
    ● Avoid using Git repositories as gem sources
    ○ as long as you can
    

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27. The More You Layer, the More It Gets Bigger
    Deleting existing files does not decrease the whole size
    Exploring the layers of an image with github.com/wagoodman/dive
    

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28. Drop build-time deps w/ multi-stage build
    Node.js, NPM and node_modules can be removed in the
    same way
    https://docs.docker.com/develop/develop-images/multistage-build/
    

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29. Avoid Git source if possible
    gem ‘rails’, github: ‘rails/rails’ loads...
    

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30. Generated Files Are Owned By root
    

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31. Generated files are owned by root
    

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32. Plan A: Add a user
    Add a user with the same UID as the user on the host
    

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33. Plan B: userns-remap
    Or, adjust the UID seen from the host with userns-remap
    

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34. Long/Complex Commands
    

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35. A kind of typing game?
    More than twice as long as the original command!
    $ docker-compose exec rails bin/rails g model User
    email:string
    $ docker-compose exec rails bin/rails db:migrate
    $ docker-compose exec rails bin/rails c
    

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36. Binstubs?
    Ended up with creating dedicated binstubs for each project
    

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37. Exec vs. Run; Which should I use?
    It depends...
    ● docker-compose exec
    ○ Uses an already running container
    ○ Can’t publish additional ports
    ● docker-compose run
    ○ Creates and uses a dedicated container
    ○ Without `--use-aliases`, couldn’t resolve some of the host names in some cases
    ○ Without `--rm`, the created container will remains after exit
    

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38. Crane
    Cosy interface to develop
    ● Reads docker-compose.yml
    ● Grouping services
    ● There’s only `run`
    ○ Works nicely by the situation
    

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39. Could We Develop Apps w/ K8s?
    

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40. Is Kubernetes only for production?
    

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41. Why don’t you use the same tool
    https://speakerdeck.com/mtsmfm/development-env-in-the-microservices-age
    

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42. Is it possible to develop apps w/ K8s?
    Yup.
    ● Good news: We can use the same tool for development
    ● Bad news: We will have to manage a lot of YAML files
    ○ Because of the difference of the API
    ○ Because K8s projects tend to be large
    ○ For not only production, but also development
    

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43. Organize YAML files w/ Kustomize
    https://github.com/kubernetes-sigs/kustomize
    

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44. Et cetera...
    

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45. References
    ● Docker for Rails Developers
    ● gh.c/esminc/rails-docker-examples
    

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46. Example Repository
    https://github.com/esminc/rails-docker-examples
    ● Example Rails app + PostgreSQL + Webpacker
    ● Configurations for Docker Compose
    ● Configurations for Kubernetes (w/ GKE)
    

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