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.
2. Hi there • Gentaro Terada (@hibariya) • Works at ESM, Inc. • A college student (engineering) • Likes Ruby, Internet, and Programming • https://hibariya.org
3. Today we will talk about: • Why/How to use Docker • Problems/questions I faced
4. Why To Use Docker
5. What is Docker With Docker, we can: • Create/run containers • Create/share container images (kind of snapshots)
6. Container is lighter Container vs. Virtual Machine https://www.docker.com/resources/what-container
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
8. How To Use Docker
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
10. Dockerfile for a Rails app
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 …
12. docker-compose.yml to Organize
13. Invoke the app $ docker-compose run --rm rails bin/setup $ docker-compose up
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
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)
16. Problems I Faced
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?
18. Testing with Browsers
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
20. docker-compose.yml test/application_system_test_case.rb
21. Interactive Debugging with VNC Stop w/ a breakpoint, connect to localhost:5900 w/ VNC
22. Dockerfile Doesn’t Ensure the Same Image
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
24. Share the image
25. Too Large Images
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
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
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/
29. Avoid Git source if possible gem ‘rails’, github: ‘rails/rails’ loads...
30. Generated Files Are Owned By root
31. Generated files are owned by root
32. Plan A: Add a user Add a user with the same UID as the user on the host
33. Plan B: userns-remap Or, adjust the UID seen from the host with userns-remap
34. Long/Complex Commands
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
36. Binstubs? Ended up with creating dedicated binstubs for each project
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
38. Crane Cosy interface to develop • Reads docker-compose.yml • Grouping services • There’s only `run` ◦ Works nicely by the situation
39. Could We Develop Apps w/ K8s?
40. Is Kubernetes only for production?
41. Why don’t you use the same tool https://speakerdeck.com/mtsmfm/development-env-in-the-microservices-age
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
43. Organize YAML files w/ Kustomize https://github.com/kubernetes-sigs/kustomize
44. Et cetera...
45. References • Docker for Rails Developers • gh.c/esminc/rails-docker-examples
46. Example Repository https://github.com/esminc/rails-docker-examples • Example Rails app + PostgreSQL + Webpacker • Configurations for Docker Compose • Configurations for Kubernetes (w/ GKE)