Ruby on rails with jRuby

Question

I'm working on a Ruby on Rails app, currently hosted on Heroku. We have about 5 web dynos and about 2 worker process running on average. But because we're using adeptscale these can change a lot, and the cost is increasing from month to month.

We're thinking about changing the process and the infrastructure (using our own, off of amazon/google etc). And also because of the performance, access to java libraries and other gains we're planning to go with jRuby.

I haven't got much experience with jRuby at all, but I do have Java experience. So I have a few questions:

Question intro: Since rails philosophy/approach differs from Javas, ie ruby webserver uses far less memory but can only process one request at a time, and so having multiple servers sort of compensates the inability to process multiple requests.

1. If we go with jRuby (and have our rails project packaged as a war file and deployed to any servlet container ie Tomcat or Jboss(more than just container)), will we be able to process multiple requests then?

Question intro: Currently we got some application logic running in the workers(instead of blocking the webserver, and not being able to serve other clients/browser clients). ie when users submit some form and then our app needs to contact the 3rd party service to return the response, we simply let the worker do the workload of getting back from the 3rd party service and updating the ui (which reports waiting status) via websockets that the 3rd party service returned x/y or whatever status.

2. If we switch to jRuby, how will we achieve the similar logic? I mean do we go with the java code which has some kind of thread pool of workers and then free workers do the workload of contacting the 3rd party service etc? How would we go about this if we decide to go with jRuby?

Answer 1

1) You can serve multiple requests at a time in jruby with nearly any container, but you can also serve multiple requests at a time with mri-ruby . You only have to have a threadsafe app (config.threadsafe! is default in rails4). Different rack servers have different approaches to serve multiple requests at a time. For example unicorn uses multiple processes while passenger or puma go for a multi-threaded approach .

In my experience jruby containers like jboss or tomcat are more complicated to configure properly. But there are things like tourquebox , trinidad that help you with this. But you can even still go for some of the ruby servers (eg puma) that dont use c extensions.

2) If I understand you correctly you are looking for some background-processing library? You can use sidekiq or resque with ruby or jruby (while jruby will be faster in general, and its easier to debug memory leaks). You can even use ruby for your rack servers and jruby for your workers (can even be run in parallel with things like rvm/rbenv)

In general I would only go for the jruby option if you know what you are doing and need better performance for your app servers or if you want to speed up your worker servers. If I was you I would probably stay in the ruby world and use puma for your app and sidekiq as a background service . Both are very elegant and need not so much configuration.

Answer 2

1. Yes, JRuby uses Java threads and is really multithreaded. And I can say that it's really good in integration with Java, even using classes for JNI. I can recommend next servers (some have already been mentioned):
   • puma ( https://github.com/puma/puma )
   • any servlet container (even IBM WebSphere Application Server!) - just use warbler ( https://github.com/jruby/warbler )

The 'simplest' way to run application on servlet container is make .war with warbler. Usually resulting .war file includes all dependencies and JRuby interpreter, so resulting file usually is 30 Mb. But I think that it is not so easy to setup warbler, then I wouldn't recommend this way if you don't really need to run Rails in enterprise Java environment.

And I would just remind that Rails opens DB connection for any request, then default size of DB connection pool of 5 isn't enough - don't forget to increase it before load testing :) (eg default thread pool for puma is 16, IBM WAS is 50, Tomcat - 200 threads).

I agree with smallbutton.com that puma is good choice. Finally, with puma you can switch between JRuby and other interpreter almost easy (in my experience there is one difference - gem's names)