enable remote debugging in docker


I try to implement remote debugging like explained here:


I have a jruby 9.1 rails application running in docker.

In my Gemfile I have under the development section -->

gem  'debase', '~>0.2.2.beta10', require: false

However, I get an error on "docker build"


Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /usr/local/bundle/gems/debase-0.2.2.beta10/ext
/opt/jruby/bin/jruby -r ./siteconf20170609-7-1ef9cbf.rb extconf.rb
checking for vm_core.h... RuntimeError: The compiler failed to generate an
executable file.
You have to install development tools first.


I have development tools installed in docker ! -->

fetch http://dl-cdn.alpinelinux.org/alpine/v3.5/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.5/community/x86_64/APKINDEX.tar.gz
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Executing abuild-2.29.0-r2.pre-install
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RUN apk add --update alpine-sdk

from my Dockerfile.


My mkmf.log file looks:

" -o conftest -I/include/universal-java1.8 -I/opt/jruby/lib/ruby/include/ruby/backward -I/opt/jruby/lib/ruby/include -I.     -fPIC  -fno-omit-frame-pointer -fno-strict-aliasing  -fexceptions  conftest.c  -L. -L/opt/jruby/lib    -m64      "
checked program was:
/* begin */
1: #include "ruby.h"
3: #include <ruby.h>
4: int main(int argc, char **argv)
5: {
6:   return 0;
7: }
/* end */

which looks strange to me because I would expect starting this line with "gcc -o ...". And gcc is installed.

Any advise?








Hello Thomas, 

in case you're using jruby debug gems are ruby-debug-ide and ruby-debug-base so please check how it goes with them. 


Hello Olga,

thank you. I'm now close to debugging ;-) I think.

I followed your advise and the build failure disappeared.

My Gemfile looks now like:

group :development, :test do
gem 'ruby-debug'
gem 'ruby-debug-base'
gem 'ruby-debug-ide'

My first problem was that I still got a error at runtime when I started the rails application complaining that rdebug-ide needs some other gems not installed.

So I expanded my Gemfile until the rails-app started successful in the container.

The lines before

  gem 'ruby-debug-base'
gem 'ruby-debug-ide'

are now (inside 'group :development, :test do'):
gem  'i18n', '0.8.1'       # needed by von rdebug-ide 
gem 'minitest', '5.10.1' # needed by von rdebug-ide
gem 'rack', '1.6.5' # needed by von rdebug-ide
gem 'mail', '2.6.4' # needed by von rdebug-ide
gem 'rack-protection', '1.5.3' # needed by von rdebug-ide
gem 'rainbow', '2.2.1' # needed by von rdebug-ide
gem 'rspec-support', '3.5.0' # needed by von rdebug-ide
gem 'sass', '3.4.23' # needed by von rdebug-ide
gem 'ruby-debug-base'
gem 'ruby-debug-ide'

This was a really timeconsuming task. It first failed with a missing i18n, then with a missing minitest ...
Why was it not automatically resolved?

In my Dockerfile I had before debugging:

CMD puma -e $RAILS_ENV

Now with debugging I do:

CMD bundle exec rdebug-ide --host --port 1234 --dispatcher-port 26162 -- /usr/local/bundle/gems/puma-3.8.2-java/bin/puma -e $RAILS_ENV


This are the first two lines from the docker-railscontainer-logfile:

eb_1         | /usr/local/bundle/gems/ruby-debug-base-0.10.6-java/lib/ruby-debug-base.rb:196: warning: tracing (e.g. set_trace_func) will not capture all events without --debug flag
web_1         | Fast Debugger (ruby-debug-ide 0.6.0, ruby-debug-base 0.10.6, file filtering is supported) listens on


Now the real problem:
I can attach from rubymine to the docker process. In the Rubymine debug-variables window I see an info "Connected"
with a blue/white exclamation mark in front.

BUT when I set a breakpoint in the code the execution does not stop when I come to this code line!


Hello Thomas,

sorry for the delay. There are some parameters that need to be passed to jruby. That probably might be done via JRUBY_OPTS (https://stackoverflow.com/questions/8283300/how-do-i-use-jruby-opts-with-rvm). You need to pass the following:

-J-Djruby.objectspace.enabled=true -J-Djruby.compile.mode=OFF -J-Djruby.debug.fullTrace=true


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