title: Rails: Could not find concurrent-ruby-1.0.5 in any of the sources (Bundler::GemNotFound)
body: <p>I've Googled this quite a bit, and haven't found anything useful to my situation.</p>
  
  <p><code>$ docker-compose up abc</code></p>
  
  <p>produces the following in the logs:</p>
  
  <pre><code>/usr/lib/ruby/vendor_ruby/bundler/spec_set.rb:92:in `block in materialize': Could not find concurrent-ruby-1.0.5 in any of the sources (Bundler::GemNotFound)
     from /usr/lib/ruby/vendor_ruby/bundler/spec_set.rb:85:in `map!'
     from /usr/lib/ruby/vendor_ruby/bundler/spec_set.rb:85:in `materialize'
     from /usr/lib/ruby/vendor_ruby/bundler/definition.rb:132:in `specs'
     from /usr/lib/ruby/vendor_ruby/bundler/definition.rb:177:in `specs_for'
     from /usr/lib/ruby/vendor_ruby/bundler/definition.rb:166:in `requested_specs'
     from /usr/lib/ruby/vendor_ruby/bundler/environment.rb:18:in `requested_specs'
     from /usr/lib/ruby/vendor_ruby/bundler/runtime.rb:13:in `setup'
     from /usr/lib/ruby/vendor_ruby/bundler.rb:121:in `setup'
     from /usr/lib/ruby/vendor_ruby/bundler/setup.rb:17:in `&lt;top (required)&gt;'
     from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
     from /usr/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
  </code></pre>
  
  <p>The relevant bit from my docker-compose.yml file:
  <code>command: bundle exec rails server</code></p>
  
  <p>concurrent-ruby is most definitely installed, exactly where it needs to be. I've run <code>bundle install</code> inside Docker so many times, and I've tried adding <code>gem install concurrent-ruby -v 1.0.5</code> to my docker-compose command, and it installs just fine, and then still complains that it can't find the gem. I tried adding <code>bundle install</code> directly to my docker-compose command, and that fails because of some known issue involving docker-compose and git (I'm using two internal gems). [ EDIT: <a href="https://github.com/docker/compose/issues/2856#issuecomment-236625662" rel="noreferrer">https://github.com/docker/compose/issues/2856#issuecomment-236625662</a> ]</p>
  
  <p>Everything worked fine until I upgraded some Ruby gems, but I'm not sure why or how to fix it.</p>