missing dependencies for gem installation

[devoops0]

Problem

gem install fluent-plugin-splunk-ex fails with the following message:

ERROR:  Error installing fluent-plugin-splunk-ex:
	ERROR: Failed to build gem native extension.

    /usr/bin/ruby extconf.rb
mkmf.rb can't find header files for ruby at /usr/share/include/ruby.h


Gem files will remain installed in /opt/app-root/src/gems/msgpack-0.5.12 for inspection.
Results logged to /opt/app-root/src/gems/msgpack-0.5.12/ext/msgpack/gem_make.out

Fix

The installation fails due to missing dependencies.
Dependencies can be resolved by installing gcc make ruby-devel

To acocmplish this, I had to adjust the Dockerfile like this:

FROM registry.access.redhat.com/openshift3/logging-fluentd:latest

RUN yum-config-manager --enable rhel-7-server-rpms rhel-7-server-optional-rpms

RUN yum install -y gcc make ruby-devel

RUN gem install -N --conservative --minimal-deps --no-document \
       'activesupport:<5' \
       fluent-plugin-secure-forward \
       fluent-plugin-kubernetes_metadata_filter \
       fluent-plugin-rewrite-tag-filter \
       fluent-plugin-secure-forward \
       fluent-plugin-remote_syslog \
       fluent-plugin-record-modifier \
       fluent-plugin-splunk-ex

RUN yum remove gcc make ruby-devel

RUN yum autoclean

RUN yum-config-manager --disable rhel-7-server-rpms rhel-7-server-optional-rpms

RUN rm -rf /var/cache/yum/*