Session Storage in JRuby on Rails

There are many ways to store sessions in Ruby on Rails, but by using JRuby, we get another option that I think supersedes the common solutions... Using the Java Server's built in session store.

First... The implementation

This is assuming that you are running JRuby and using a tool like warbler to deploy to a Java server like Tomcat.

config/initializers/session_store.rb

# check if we're running in a java container
if defined?($servlet_context)
    require 'action_controller/session/java_servlet_store'
    # tell rails to use the java container's session store
    ActionController::Base.session_store = :java_servlet_store
else
    # other session store for development in webrick/mongrel
    # setup cookie based session
    ActionController::Base.session = {
        :key    => '_dd_session',
        :secret => '<Your really long random secret key>'
    }
end

This will store your rails session in Tomcat's session store exactly as if you were running a Java web framework.

Second... Why?

There are a few common solutions starting with the rails default.

Cookie Store: This is not very secure, limited in size, and sends a lot of data back and forth to the client. It is strongly recommended to not use this for production systems.
File Store: Stores sessions on the file system. Every cookie access involves file system IO. Does not support clustering by default but can be achieved through a SAN or shared storage.
ActiveRecord: Stores sessions in the database. Slow due to database IO. Natively supports clustering.
Memcached: Stores sessions in Memcached instance. Very popular and works well with clusters. Can run into RAM issues on systems with lots of users. Requires an instance of Memcached running.
Java Servlet Store: Works just like your other Java applications. Java Servers can be configured to cluster sessions. Uses the JSESSIONID cookie or url param (in Tomcat)

Conclusion

This won't be the solution for everyone, but if you're deploying a JRuby on Rails app into an infrastructure based on Java, then it provides a simple and efficient solution.