# AWD page 624-626 Understanding how Apache, Mongrel and Rais

**URL:** <https://www.ruby-forum.com/t/awd-page-624-626-understanding-how-apache-mongrel-and-rais/91579>\
**Category:** Rails\
**Created:** [April 10, 2007, 6:00pm UTC](https://www.ruby-forum.com/t/awd-page-624-626-understanding-how-apache-mongrel-and-rais/91579 "2007-04-10T18:00:33Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![bravedave](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/46a35a/32.png) [@bravedave](https://www.ruby-forum.com/u/bravedave)\
**Post date:** [April 10, 2007, 6:00pm UTC](https://www.ruby-forum.com/t/awd-page-624-626-understanding-how-apache-mongrel-and-rais/91579/1 "2007-04-10T18:00:33Z")

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I’m trying to understand the ‘Big Picture’ of how Ruby on Rails  
applications are deployed and operate in distributed environment (one  
deployment server, many remote servers).  
I follow AWD by Dave T.’ explanation from pages 624-626. From  
reading these pages I have these questions;

1. How does the RonR instance on the ‘remote’ server gain access to  
the program logic to process the HTTP request?

2. Is Mongrel the actual program running that receives the HTTP  
request and runs the code against the RonR libraries and the  
application code?

3. How does Mongrel know where the ‘remote’ servers are located?

4. Where is Mongrel running when there’s an environment like this, on  
the deployment or remote server?

5. How does Apache know what port to send the request out on? In his  
example they have ports 8000 and 8001.

6. If Apache’s job is to send the requests out on a particular port,  
then why does it need to know where the program code resides (as shown  
in it’s page 626 script).

David

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<div class="post-metadata">

**Author:** ![bravedave](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/46a35a/32.png) [@bravedave](https://www.ruby-forum.com/u/bravedave)\
**Post date:** [April 10, 2007, 9:06pm UTC](https://www.ruby-forum.com/t/awd-page-624-626-understanding-how-apache-mongrel-and-rais/91579/2 "2007-04-10T21:06:04Z")

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BraveDave wrote:

> I’m trying to understand the ‘Big Picture’ of how Ruby on Rails  
> applications are deployed and operate in distributed environment (one  
> deployment server, many remote servers).  
> I follow AWD by Dave T.’ explanation from pages 624-626. From  
> reading these pages I have these questions;
> 
> 1. How does the RonR instance on the ‘remote’ server gain access to  
> the program logic to process the HTTP request?

Not sure I understand this question. Once you deploy your rails app to a  
a remote server, it _is_ the program logic to process the HTTP request.  
For now, maybe don’t worry about “remote”… try to get your head around  
what apache and mongrel do.

> 1. Is Mongrel the actual program running that receives the HTTP  
> request and runs the code against the RonR libraries and the  
> application code?

The standard port for the WWW is 80. So something needs to respond to  
web requests on port 80 on your server. Rails code is single-threaded,  
so in order to handle concurrent requests using mongrel, you have to  
start multiple mongrel processes. These can’t all answer on port 80, so  
you need a web server (or just a load balancer) like apache (or nginx,  
pen, pound, lighttpd, etc.) to receive the request on port 80 and  
forward it to one of your mongrel instances.

> 1. How does Mongrel know where the ‘remote’ servers are located?

Mongrel _is_ on the remote server.

> 1. Where is Mongrel running when there’s an environment like this, on  
> the deployment or remote server?

The remote server… One could always have a more sophisticated setup  
with separate machines for different roles… uh, but no one usually  
speaks of a “deployment” server. The idea of capistrano is that you run  
commands on you local machine and it executes them on the server  
(including checking out code from a repository server).

> 1. How does Apache know what port to send the request out on? In his  
> example they have ports 8000 and 8001.

You configure mongrel\_cluster (usually in  
/etc/mongrel\_cluster/myapp.yml) to start a certain number of instances  
on certain ports. You set up the apache config to proxy the requests to  
the ports that you configure mongrel to listen on.

> 1. If Apache’s job is to send the requests out on a particular port,  
> then why does it need to know where the program code resides (as shown  
> in it’s page 626 script).

I think you mean the sample apache config on page 625 (at least in my  
copy of the pdf)… as in setting the DocumentRoot. If so, this is the  
other reason for putting a web server in front of mongrel… it can  
(theoretically) serve static files faster.

Notice that that config ends in /current/public… it is setting the  
rails app’s public directory – with all the images, stylesheets and  
other static resources as the document root for this virtual host.

Hope some of this helps…

b