Docker + Rails のdocker-compose build でGemNotFoundExceptionの時の対処

対象者

docker-compose build や docker-compose up で GemNotFoundException が吐き出されたときの対処法

エラー内容

/usr/local/lib/ruby/2.6.0/rubygems.rb:283:in `find_spec_for_exe': Could not find 'bundler' (2.0.2) required by your /myapp/Gemfile.lock. (Gem::GemNotFoundException)
To update to the latest version installed on your system, run `bundle update --bundler`.
To install the missing version, run `gem install bundler:2.0.2`
        from /usr/local/lib/ruby/2.6.0/rubygems.rb:302:in `activate_bin_path'
        from /usr/local/bin/bundle:23:in `<main>'
ERROR: Service 'web' failed to build: The command '/bin/sh -c bundle install' returned a non-zero code: 1

#経緯
https://kic-yuuki.hatenablog.com/entry/2019/02/25/091235
https://qiita.com/at-946/items/f6fbf0115d373ce58be5
これらを参考に bootstrap から Materialize に移行しようとしてました。
そこでGemfileに追加してbundle install し、docker-compose build でエラーが吐かれました。

#原因
bundler のバージョンが違うため。

#解決法
Dockerfile にbundle install する前に gem install bundler を走らせればとりあえず解決。

Dockerfile

FROM ruby:2.6.3

RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - \
        && apt-get install -y nodejs

RUN apt-get update -qq && apt-get install -y build-essential libpq-dev postgresql-client

RUN apt-get update && apt-get install -y curl apt-transport-https wget && \
curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - && \
echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list && \
apt-get update && apt-get install -y yarn

RUN mkdir /myapp
WORKDIR /myapp
ADD Gemfile /myapp/Gemfile
ADD Gemfile.lock /myapp/Gemfile.lock
RUN bundle install
COPY . /myapp

CMD ["rails", "server", "-b", "0.0.0.0"]

Dockerfile

++ RUN gem install bundler

Dockerfile

FROM ruby:2.6.3

RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - \
        && apt-get install -y nodejs

RUN apt-get update -qq && apt-get install -y build-essential libpq-dev postgresql-client

RUN apt-get update && apt-get install -y curl apt-transport-https wget && \
curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - && \
echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list && \
apt-get update && apt-get install -y yarn

RUN mkdir /myapp
WORKDIR /myapp
ADD Gemfile /myapp/Gemfile
ADD Gemfile.lock /myapp/Gemfile.lock
RUN gem install bundler
RUN bundle install
COPY . /myapp

CMD ["rails", "server", "-b", "0.0.0.0"]