Docker Ruby Bundler not installing - ruby

Question

My Dockerfile looks like below:
FROM ruby:2.5-alpine
RUN apk update add --no-cache build-base nodejs postgresql-dev
RUN mkdir /my-app
WORKDIR /my-app
COPY Gemfile Gemfile.lock ./
RUN bundle install --binstubs
COPY . .
CMD puma -C config/puma.rb
Now when I try to create an image, it gives following error:
You must use Bundler 2 or greater with this lockfile.
The command '/bin/sh -c bundle install --binstubs' returned a non-zero code: 20
The bundler version Gemfile.lock using is 2.1.4.
I did tried adding following line to Dockerfile:
RUN gem update --system
RUN gem install bundler -v 2.1.4
In that case, I get following error:
ERROR: Could not find a valid gem 'bundler' (= 2.1.4), here is why:
Unable to download data from https://rubygems.org/ - no such name (https://rubygems.org/specs.4.8.gz)
I am using Ubuntu 18.04 system. Anyone had faced this issue before? Any help appreciated.
Thank you in advance.

Answer 1

FROM ruby:2.5-alpine
RUN apk update add --no-cache build-base nodejs postgresql-dev
RUN mkdir /my-app
WORKDIR /my-app
RUN gem update --system
RUN gem install bundler -v 2.1.4
COPY Gemfile Gemfile.lock ./
RUN bundle install --binstubs
COPY . .
CMD puma -C config/puma.rb
So, installing bundler was fine but due IPV6 of rubygems.org is still broken and create issue while fetching inside docker. So, i ran the command using host network.
docker image build --network=host -t my-app .
And this issue was resolved.
Thanks for taking time.

Answer 2

I need to create an answer since I can not post this all into a comment. I realize that this is not a solution for you.
If I use this setup, It runs without an error. Can you please look where it differs from your setup and tests? (please also add this to the question)
dockerfile
FROM ruby:2.5-alpine
RUN apk update add --no-cache build-base nodejs postgresql-dev
RUN mkdir /my-app
WORKDIR /my-app
RUN gem update --system && gem install bundler && bundle --version
# installs bundler 2.1.4
COPY Gemfile Gemfile.lock ./
RUN bundle install
COPY . .
CMD /bin/sh
Gemfile
ruby '2.5.8'
source 'https://rubygems.org'
gem 'flay'
Gemfile.lock
GEM
remote: https://rubygems.org/
specs:
erubis (2.7.0)
flay (2.12.0)
erubis (~> 2.7.0)
path_expander (~> 1.0)
ruby_parser (~> 3.0)
sexp_processor (~> 4.0)
path_expander (1.0.3)
ruby_parser (3.13.1)
sexp_processor (~> 4.9)
sexp_processor (4.12.0)
PLATFORMS
ruby
DEPENDENCIES
flay
RUBY VERSION
ruby 2.5.8p224
BUNDLED WITH
2.1.4
Build and started with:
docker build . --no-cache -t foobar
docker run --it foobar