Solr gem and xml ruby gem How it matters

If you use solr-ruby gem, you should be well aware that Solr attempts to create an XML doc from the provided doc-hash. It first attempts to use 'xml/libxml', which if not available, falls back to REXML. It is recommended to use libxml.

All you need to do is

gem install libxml-ruby

If you are lucky enough, that's all for you. However, many a times we face issues like

Building native extensions.  This could take a while...
ERROR:  Error installing libxml-ruby:
	ERROR: Failed to build gem native extension.

/usr/bin/ruby extconf.rb
checking for socket() in -lsocket... no
checking for gethostbyname() in -lnsl... yes
checking for atan() in -lm... no
checking for atan() in -lm... yes
checking for inflate() in -lz... no
checking for inflate() in -lzlib... no
checking for inflate() in -lzlib1... no
checking for inflate() in -llibz... no
*** 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.

If this is the case, you should install zlib-devel and libxml2-devel packages.

yum -y install zlib-devel
yum -y install libxml2-devel
gem install libxml-ruby

That sorts it all. You are good to go