Some fundamental architectural insights on the Ruby On Rails technology compared to Java

Rails
1

Hi guys,

It’s a pleasure for me to join your community mailing list. I am a
keen software engineer and experimenter, and happen to investigate and
dive into the Ruby language from a couple of weeks. So far i have
become familiar with the basics of the syntax and semantics of the
language, and, of course, i would like to get to know the Ruby web
application framework Rails too. But i enjoy understanding the
principles which a software platform relies on, so i would kindly like
to ask you some questions about the architecture of the Rails
framework that i couldn’t find by googling , and would highly
appreciate your comments and answers.

Since i come from the JavaSE and JavaEE world, its inevitable for me
to try to use the analogy principles between Ruby and Java. In JavaSE
we write standalone applications, which we execute over a JVM. In
JavaEE we can write web applications, which require a JavaEE web
server and container to be deployed in (and of course, underlying the
container there is a JVM).

In the classical Ruby scenario, we write standalone applications,
which we run on Ruby VM (there are a lot of VMs, implemented in
different languages). But when it comes to writing Ruby web
applications on Rails, we need some more sophisticated execution
environment, such as a Rails web server - WEBrick, Mongrel, etc. Am i
already getting it wrong ? Are WEBrick, Mongrel the Ruby analogies of
a JavaEE application server, or they are actually something completely
different?

Google says that Mongrel is a web server, but isn’t Mongrel also
executing Ruby code ?

It seems that to execute a Rails application, one needs a Ruby VM and
a Ruby web server (and of course, the Rails framework itself
installed). But where is the application code executed - directly in
the Ruby VM, or inside the Ruby web server (as is in JavaEE: servlets/
JSPs are executed inside the web container) ? That means, what exactly
is a Ruby web server doing in the whole picture ? Is it just
dispatching HTTP requests to Ruby classes to handle them, i.e. it is
only a mediator ? Or is it executing the application code, just like a
web container that executes servlet code ?

I would highly appreciate any guidance on this, since so far i cannot
answer these questions.

Kindest Regards,
Krum.

2

On Fri, Feb 19, 2010 at 10:41 AM, Krum B. [email protected]
wrote:

executing Ruby code ?
In that analogy you can think Mongrel is something similar to Tomcat.
It is a web server, but one that can also serve Rails applications.

Rails has an entry point to a request, the dispatcher, and Ruby-based
web servers are able to execute Rails request because they have code
that knows how to call the Rails dispatcher. From that point downwards
it is Rails business to handle the request. The contract is that the
dispatcher returns a response object that the container manages to
send back to the client.

You can also have Apache or Nginx, etc. as front-ends. As you can with
a servlet container. In that case you either configure the server to
proxy dynamic calls to a set of known mongrels that are running
somewhere. Or you can also forget about all that stuff and use an
Apache/Nginx module called Passenger which handles everything for you
and it just needs that you configure the document root of your Rails
application. The latter is the most common production setup nowadays.

That’s more or less the picture.

3

Xavier N. wrote:

On Fri, Feb 19, 2010 at 10:41 AM, Krum B. [email protected]
wrote:

executing Ruby code ?
In that analogy you can think Mongrel is something similar to Tomcat.
It is a web server, but one that can also serve Rails applications.

Another important piece of this puzzle when relating to new versions of
Rails is Rack:

http://rack.rubyforge.org/

Rails applications for the past sever versions are built on top of Rack.
Phusion Passenger is an Apache or Nginx module that supports Rack
applications. This includes Rails, but also includes several other ways
to build web applications with Ruby.

If you needed something extremely simple you can build web applications
with nothing else but Rack.

Example of a functional Rack application:

class HelloWorld
def call(env)
[200, {“Content-Type” => “text/plain”}, [“Hello world!”]]
end
end

For more convenience, but without the heft of Rails, there is also
Sinatra:
http://www.sinatrarb.com/

Hope that clears things up a bit for you.

4

Thank you guys for your help!

To Xavier’s words:
So if i am understanding you correctly, Mongrel is capable of
transforming HTTP requests to invocations of the Rails dispatcher,
and, on the other side, transforming the result from the Rails
application back to a HTTP response. So it seems that Mongrel is just
a web server, that is a mediator to the Rails application, just like
the good old CGI ideology ? Which is also present in the JavaEE case,
but with the significant difference that, apart from transforming the
HTTP request to a servlet invocation, the web container is THE
execution environment, and it handles the complete life cycle of the
servlet/JSPs… In this sense, i see that Mongrel does not handle
the life cycle of the Rails component, does it ?

And fianlly, i would also like to ask you some more questions.
Consider a typical Rails application, running inside Mongrel. What
possibilities do there exist for my Ruby code (of the Rails
application) to call/execute Java code ?
What is the relation between Mongrel and Java ? From the home page of
Mongrel, after i downloaded the Mongrel archive, it seems that it is
an application, written in pure Ruby (except for the HTTP parser,
which could be written in C or Java). What is the Mongrel <-> Java
integration ?

5

On Feb 22, 8:48 am, Krum B. [email protected] wrote:

HTTP request to a servlet invocation, the web container is THE
execution environment, and it handles the complete life cycle of the
servlet/JSPs… In this sense, i see that Mongrel does not handle
the life cycle of the Rails component, does it ?

what does life cycle mean? The entirety of the request is handled
inside the instance of mongrel in question.

And fianlly, i would also like to ask you some more questions.
Consider a typical Rails application, running inside Mongrel. What
possibilities do there exist for my Ruby code (of the Rails
application) to call/execute Java code ?
What is the relation between Mongrel and Java ? From the home page of
Mongrel, after i downloaded the Mongrel archive, it seems that it is
an application, written in pure Ruby (except for the HTTP parser,
which could be written in C or Java). What is the Mongrel ↔ Java
integration ?

I believe that the bits written in C have also been implemented in
java too, so you could run mongrel on jruby, which makes calling java
code pretty easy (although I believe that people using jruby tend to
use options like glassfish rather than mongrel)

Fred

6

On Feb 22, 11:05 am, Krum B. [email protected] wrote:

Thank you, Fred.

Could you please elaborate some more on the Mongrel ↔ JRuby
connection ?
If i run Mongrel on JRuby, how does ease me with calling Java code ?

jruby is written in java (hence the j). Have a look at the jruby docs,
they’ve got a big chunk on java/ruby integration (
http://kenai.com/projects/jruby/pages/CallingJavaFromJRuby )

Fred

7

Thank you, Fred.

Could you please elaborate some more on the Mongrel <-> JRuby
connection ?
If i run Mongrel on JRuby, how does ease me with calling Java code ?

Thanks!
Krum.