Rails 6 running on Docker with bundler -v 2.0.2 installed... You must use Bundler 2 or greater with this lockfile

Question

I'm adding a new Rails 6 / Ruby 2.6 / Postgres app to Docker, however whenever I try to run a rake command (eg. docker-compose run web rake db:setup) within the container, I get:

You must use Bundler 2 or greater with this lockfile.

I've tried explicitly installing Bundler 2.0.2 within the container, however no luck.

Running within the Rails container, bundler-v returns 2.0.2,

root@114f7d6a2b72:/app# bundler -v
Bundler version 2.0.2

Within the Gemfile.lock:

RUBY VERSION
   ruby 2.6.0p-1

BUNDLED WITH
   2.0.2

And within the Dockerfile:

FROM ruby:2.6.0
...more stuff...
COPY Gemfile Gemfile.lock package.json yarn.lock ./
RUN gem install bundler -v 2.0.2
RUN bundle install --verbose --jobs 20 --retry 5

This seems so simple, and yet I can't get it to work. What am I missing?

Answer 1

from the Docs, you must run gem update --system to upgrade the bundel and I suggest also to use ruby:2.6.1