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Docker Basics for Rails Discussion

Discussion for Docker Basics for Rails

If I run rails inside of Docker, does this set-up require more resources from my my machine?

Hey Chris, when I downloaded the Source Code GitHub repo and ran docker-compose up, it couldn't build sqlite3.

I tried adding a dependency for sqlite-dev in the Dockerfile, then it worked.
I opened a corresponding PR in your repo to add the dependency.

Great episode! I already use Docker for local development and I love it. Are you planning to do an episode to explain how to deploy a dockerized rails application? It seems very obscure to me.

Thanks for the great tutorial! I am a beginner in dockerizing rails app and get started with this tutorial. I realized some optimization may have been omitted to keep the tutorial concise. Following are some optimization tricks I found useful if starting from the Dockerfile :)

  1. Add (at least) node_modules and .git into a .dockerignore file, so the COPY . /app/ step could skip these files. (This could save you a log of time/docker image size when .git is huge)

  2. Avoid the error: 'A server is already running. Check /project/tmp/pids/ Exiting' with an script.
    Refer to Docker docs - Sample applications - Rails and PostgreSQL for the complete script, and don't forget to change #!/bin/bash to #!/bin/sh since we are using Alpine in this tutorial.

  3. Avoid needing to run yarn install again after change the source code and re-build image.
    Instead of:

COPY . /app/

RUN yarn install
RUN bundle install


COPY package.json yarn.lock /app/
RUN yarn install
COPY Gemfile Gemfile.lock /app/
RUN bundle install
 # Steps above could be cached most of the time when re-building image

 # Copy source code after dependencies installed
COPY . /app/

I'm using this solution and it save a lot of time.
I strongly encourage using this technique with Selective disable caching

So you can put this step befor copy your source code from local to image

Would this prevent gems from being re-installed every time you build the image, even when you did not make any changes to Gemfile?

This is great, please more docker + rails tutorials. I would like to see how to not re-install all gems if you rebuild the image but have not changed the Gemfile at all.

I agree with Drazen. More Docker+Rails tutorials. Especially on how to deploy to production. Also, how to add sidekiq.

Second this! Probably needs to be tweaked but here's my docker-compose.yml that currently works for local dev with sidekiq

    image: postgres:10.4-alpine
      - ./env/common.env
      - ./env/dev.env
      - 5432:5432
      - postgres:/var/lib/postgresql/data

    image: redis:4.0-alpine
      - 6379:6379
      - redis:/data

  app: &app_base
      context: .
        - BUNDLE_WITHOUT=production
      - ./env/common.env
      - ./env/dev.env
    command: bundle exec puma -C config/puma.rb
      - 3000:3000
      - .:/app
      - postgres
      - redis
    stdin_open: true
    tty: true

    <<: *app_base
    command: bundle exec sidekiq -C config/sidekiq.yml
    ports: []
    stdin_open: false
    tty: false


Note - in the docker file you can't have the last 2 lines of the tutorial triggering rails s

What if I have a windows computer and dont want to install ruby on the computer. Can I create a docker environment that has ruby and rails installed and where I do all the development, editing, rails new inside the image. Even run vscode outside and ssh into the image. Is that possible, and do you have a pointer for an article of yours or elsewhere to help me set that up?

You can make docker-compose create the project for you if you already have defined a Dockerfile and a docker-compose.yml:

docker-compose run --no-deps web rails new . --force --database=postgresql

See more at

Hello, I am getting this error "Don't know how to build task 'bundle' (See the list of available tasks with rails --tasks)" after running docker-compose run web bundle. Any idea why it is? Thanks

Sweet thanks for the tutorial.

Does anyone know how to deploy AN UPDATE to your rails app: for example, I've made some bug fixes.

I want to deploy these change to an already running docker container hosted on a Digital Ocean droplet.

Any ideas?

Great episode thanks Chris!
Is there another one on Docker for deploying in production?

Note to others, running Rails with dartsass-rails for your SASS compiling, you may run into segmentation violation (SEGV) errors when running the dartsass:watch command in your (valled via bin/dev by default in Rails 7+) on ALPINE Linux base images.

I tested on the standard ruby:3.1.2 vs ruby:3.1.2-alpine, and the standard image works fine but Alpine has SEGV errors. Not sure if there's an Alpine dependency that's missing that may resolve, but since I was working on local development, I didn't investigate too much and just went with the base ruby:3.1.2 image. Maybe I'll circle back once the Rails 7.1+ updates implement a default Docker setup, hopefully some folks more knowledgeable about Docker and images have resolved it for us all :)

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