Docker Rails Fix Bundler 2 problem

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In Ruby on Rails, we have Bundler to handle gem. You might be stuck with an error message You must use Bundler 2 or greater with this lockfile. when our Gemfile.lock is using Bundler version 2

$ docker-compose up rails 
             
Recreating rails ... done
Attaching to rails
rails  | Bundler::LockfileError: You must use Bundler 2 or greater with this lockfile.
...
ld-backend  | bundler: failed to load command: rails (/usr/local/bundle/bin/rails)
ld-backend exited with code 1

For this example, we will use Bundler version 2.1.4 and Ruby version 2.3.1

1. Find your bundler version at Gemfile.lock

BUNDLED WITH
   2.1.4

2. Add commandsENV BUNDLER_VERSION=BUNDLER_VERSION and RUN gem install bundler:BUNDLER_VERSION before RUN bundle install command in Dockerfile like this

FROM ruby:2.3.1
RUN apt-get update -qq && apt-get install -y apt-utils nodejs postgresql-client
# Copy project to /rails
RUN mkdir /rails
WORKDIR /rails
COPY Gemfile* ./
ENV BUNDLER_VERSION=2.1.4
RUN gem install bundler:2.1.4
RUN bundle install
COPY . .
RUN rm -f /rails/tmp/pids/server.pid
EXPOSE 3000
CMD rails server -b 0.0.0.0

3. Try to build rails without cache then start it again

For docker-compose,

$ docker-compose build --no-cache rails
$ docker-compose up rails

For docker,

$ docker build --no-cache -t rails .
$ docker run rails

4. That’s it! Enjoys 🎉

Reference

• https://stackoverflow.com/a/63158013/2398284
• https://docs.docker.com/compose/rails/