Introduction

If you look at Application Architecture, middleware is in fact the middle of the architecture. It really is the meat of a web application. From following figure, you see the MVC design pattern is implemented as a part of middleware. Actually, it is implemented on top of the middleware.

Definition of Middleware

Middleware is the "software glue" betwen the operating system and applications on each side of a client-server architecture, some refer to it as the "dash" in client-server.

Middleware could be considered as the software that provides services to applications beyond those available from the underlying operating system - it connects applications running on the server side, and pass data between them.

Middleware allows multiple processes running on different machines to interact.

Rails Middleware

• In Rails, a middleware called Rack, is automatically provided.
• Rack provides a unified and simple interface that allows applications to "talk to" web server, including Mongrel, Thin, Phusion, Apache, etc
  For example: Rack is responsible for handling HTTP requests and responses.
• Rack is used to group and organize modules, typically written in Ruby, and to specify the dependencies between them. Rack::Builder puts these together, creating a stack-like structure that can be used by a web application. To see the middleware installed in a Rails application, from the root of the application, type:

  $ rake middleware

• Other Ruby frameworks, e.g., Sinatra, are also built on top of Rack, but it doesn't have the database backend.
• For the default middleware configuration that Rails provides – it’s useful to know what’s “under the hood.”
• When you execute:

  $ rails server

  a Rack::Server object is created and attached to the web server (WEBrick by default), and the middleware components are loaded up. The Rack::Server#start method starts the web server running, listening on the designated port for HTTP requests.

References & Resources

• N/A