Problem Trying to Dockerize a Rails App with the Rugged Gem

This is a pretty specific post that I hope helps somebody out.

I’ve Dockerized a few Rails apps and it has usually been pretty easy. If I run into any problems it’s usually around a gem that uses a native C extension and the lack of some dependency that requires.

This time around I was bitten by the failure of the Rugged gem to compile. This gem requires libgit2 and will try to build it. The documentation says it requires cmake version 2.8 or greater. It also requires pkg-config. My image included both of these but I still received this error:

Installing rugged 0.27.0 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /usr/local/bundle/gems/rugged-0.27.0/ext/rugged
/usr/local/bin/ruby -I /usr/local/lib/ruby/site_ruby/2.3.0 -r
./siteconf20190108-6-sa6jzw.rb extconf.rb
checking for gmake... no
checking for make... yes
checking for cmake... yes
checking for pkg-config... yes
-- cmake .. -DBUILD_CLAR=OFF -DTHREADSAFE=ON -DBUILD_SHARED_LIBS=OFF
-DCMAKE_C_FLAGS=-fPIC -DCMAKE_BUILD_TYPE=RelWithDebInfo
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

By comitting and running the failed Docker image layer (bundle install) I was able to check mkmf.log — as the error message suggests — and determine that I was missing libssl-dev.

The following Dockerfile ended up working for me:

FROM ruby:2.3.7

RUN apt-get update && apt-get install -y \
  build-essential \ 
  cmake \ 
  software-properties-common \ 
  pkg-config \ 
  openssl \ 
  libssl-dev \ 
  nodejs

COPY Gemfile Gemfile.lock ./ 
RUN gem install bundler && bundle install --jobs 20 --retry 5

COPY . /

CMD ["rm", "-f", "/rails/tmp/pids/server.pid"]

EXPOSE 3000

Cheers,
Ryan

Ryan Bosinger

Web App Developer, Victoria BC

Problem Trying to Dockerize a Rails App with the Rugged Gem