Bundler 2 is not installing inside docker

Question

I'm trying to install bundler v2 in docker file and it installs successfully. when i run rubocop i get below error.

 warn_for_outdated_bundler_version': You must use Bundler 2 or greater with this lockfile. (Bundler::LockfileError)

which still seem to think that I am using bundler older version, how can I fix this error

Dockerfile is

FROM ruby:2.3.4-alpine

WORKDIR "/var/www/app"
COPY Gemfile Gemfile
COPY Gemfile.lock Gemfile.lock

RUN gem install bundler && bundle install

bin/bundle file is

require "rubygems"

m = Module.new do
  module_function

  def invoked_as_script?
    File.expand_path($0) == File.expand_path(__FILE__)
  end

  def env_var_version
    ENV["BUNDLER_VERSION"]
  end

  def gemfile
    gemfile = ENV["BUNDLE_GEMFILE"]
    return gemfile if gemfile && !gemfile.empty?
    File.expand_path("../../Gemfile", __FILE__)
  end

  def bundler_version
    @bundler_version ||= begin
      env_var_version || cli_arg_version ||
        lockfile_version || "#{Gem::Requirement.default}.a"
    end
  end

  def load_bundler!
    ENV["BUNDLE_GEMFILE"] ||= gemfile

    # must dup string for RG < 1.8 compatibility
    activate_bundler(bundler_version.dup)
  end

  def activate_bundler(bundler_version)
    if Gem::Version.correct?(bundler_version) && Gem::Version.new(bundler_version).release < Gem::Version.new("2.0")
      bundler_version = "< 2"
    end
    gem_error = activation_error_handling do
      gem "bundler", bundler_version
    end
    return if gem_error.nil?
    require_error = activation_error_handling do
      require "bundler/version"
    end
    return if require_error.nil? && Gem::Requirement.new(bundler_version).satisfied_by?(Gem::Version.new(Bundler::VERSION))
    warn "Activating bundler (#{bundler_version}) failed:\n#{gem_error.message}\n\nTo install the version of bundler this project requires, run `gem install bundler -v '#{bundler_version}'`"
    exit 42
  end

  def activation_error_handling
    yield
    nil
  rescue StandardError, LoadError => e
    e
  end
end

m.load_bundler!

if m.invoked_as_script?
  load Gem.bin_path("bundler", "bundle")
end

and the bundler version inside Gemfile.lock is 2.0.2

Answer 1

set BUNDLER_VERSION environment variable inside Dockerfile:

ENV BUNDLER_VERSION=2.0.2

or if you have docker.env:

BUNDLER_VERSION=2.0.2