I am learning Docker and have a little confusion that I would greatly appreciate some advice on.

When creating a new rails application. Following the guidelines of Docker's tutorial Quickstart: Compose & Rails. They're steps are as follows.

1. Create Dockerfile & Entrypoint
2. Create Gemfile with source and rails gem listed.
3. Create an empty Gemfile.lock
4. Create a docker-compose.yml and name services.
5. Generate a new rails app using docker-compose run.

The rails new command.

docker-compose run --no-deps web rails new . --force -d mysql

This is my simple Dockerfile:

FROM ruby:3.1.1-alpine3.15

RUN apk update -q
RUN apk add bash yarn git build-base nodejs mariadb-dev tzdata

WORKDIR /app

COPY Gemfile /app/Gemfile
COPY Gemfile.lock /app/Gemfile.lock

COPY package.json /app/package.json
COPY yarn.lock /app/yarn.lock

RUN gem install bundler
RUN gem update bundler
RUN bundle install

COPY entrypoint.sh /usr/bin
RUN chmod  x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]

EXPOSE 3000

This is my docker-compose.yml:

version: "3.9"
services:
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/app
    ports:
      - "3000:3000"

As you can see I only have one service listed in my docker-compose.yml, because I do not want any other services or containers.

Everything works fine when I use the command docker-compose run rails new ... it generates a new rails app and persists the files to my local source folder. So I can open and edit the files to develop the application. Perfect.

But when I try and generate a new Rails app without using docker-compose.yml and only the Dockerfile. The generated files are not persisted in my local source folder, only on the container. I can only assume because I am forced to build the image before running it in a container to generate the new rails app.

When using without docker-compose.yml. I have to build the image first.

docker build -t image_name .

Then I can run the container and generate the rails app.

docker run image_name rails new . --force -d mysql

Obviously, this doesn't persit the new files in my local source folder.

How can I generate a new Rails app with just my Dockerfile without docker compose and still have the newly generated files persist in my local source folder?

I must be missing something, but I've done a lot of research and can't find an answer.

CodePudding user response：

In docker-compose.yml you have a 'volumes' key as seen below.

volumes:
  - .:/app

But when using it in the CLI you miss passing these volumes.

You can pass these volumes as in the code below.

docker run -d --name=rails --volume /your/workdir:/app image_name

If you want to learn more about volumes, you can find out here.