ruby-scgi

ruby-scgi is a Ruby library for running Ruby on Rails (and possibly other web applications) for high-speed deployment of your applications in production. It is intended as a replacement for the ancient FastCGI code base and bring some big advantages to Rails deployment for production operations.

SCGI (Simple Common Gateway Interface) is a project to replace CGI and FastCGI with a simpler protocol to both implement and manage. It was written by Neil Schemenauer and adopted by many Python developers as a hosting option.

ruby-scgi is distributed as a gem, and can be installed with:

sudo gem install scgi

Feedback/Bugs/Support Requests should be handled through RubyForge at rubyforge.org/projects/scgi/.

The RDoc is available at scgi.rubyforge.org Source control access is available at github (github.com/jeremyevans/ruby-scgi).

Advantages

Same performance as FastCGI and better performance than other methods.
Can be used to run Rails with style (sudo gem install style)
Gives out limited status information to help manage your application’s resources.
You can set a maximum concurrent connections limit, which causes any connections over the limit to get redirected to a /busy.html file. This can help keep your site alive under heavy load.
Simple to configure with your web server.
Completely free code licensed under Rails’s own license.
No external dependencies other than Ruby

Comparison With FastCGI

SCGI and FastCGI have similar goals: To keep Ruby running between requests and process the requests as fast as possible. The difference is that SCGI is much simpler and easier to implement so there’s less chance to get it wrong.

Specifically, ruby-scgi is written in pure Ruby so it doesn’t leak memory, runs everywhere, and is easy to install (no compilers needed).

One thing that SCGI doesn’t support is using UNIX Domain sockets in addition to TCP/IP sockets. This isn’t really needed, but it is handy in a shared hosting situation where you don’t want others connecting to your processes or if you have to request open ports. Sorry, no UNIX Domain sockets in SCGI.

Comparison With WEBrick

In theory WEBrick should be able to run just as fast as ruby-scgi. They are both written in pure Ruby. They both do similar processing (although WEBrick’s are a little more complicated). They both return about the same amount of data.

In practice WEBrick in production mode runs much slower than ruby-scgi in production mode. The (dis)advantage (depending on your point of view) is that you have to manage your webserver differently than you manage your application.

Comparison With CGI

CGI is where every time a request comes in for rails the whole Ruby on Rails framework is loaded. This is very slow, but it’s easy to install.

An alternative is to use the cgi2scgi program distributed with the SCGI source available from www.mems-exchange.org/software/scgi/ along with the Apache modules. This program basically is a small little C program that runs quickly as a CGI, but passes it’s requests to your ruby-scgi backend. It’s not all that fast, but if you’re stuck with cgi-bin only access then this might be just the way to go. Since SCGI runs over TCP/IP you can even host your ruby-scgi on a totally different machine with this.

Running and Configuration

ruby-scgi is now just a library and doesn’t come with a tool to run Rails. The previous command line tool (scgi_ctrl) has been greatly enhanced and is now available as a standalone gem called ruby-style.

Example configurations

Note that ruby-scgi is only tested on Lighttpd. Also, note that Lighttpd 1.4.16 has a bug which breaks redirects using server.error-handler-404, so either use mod_magnet, use 1.4.18, or apply the patch in ticket 1270 on Lighttpd’s Trac.

Lighttpd:

server.modules = ( ... "mod_scgi" ... )
server.error-handler-404 = "/dispatch.scgi"

# For Single Process or Single-Port Clustering
scgi.server = ( "dispatch.scgi" => (
   "server1" => (
       "host" => "127.0.0.1",
       "port" => 9999,
       "check-local" => "disable",
       "disable-time" => 0)
   ))

# For Multi-Port Clustering
scgi.server = ( "dispatch.scgi" => (
   "server1" => (
       "host" => "127.0.0.1",
       "port" => 9997,
       "check-local" => "disable",
       "disable-time" => 0),
   "server2" => (
       "host" => "127.0.0.1",
       "port" => 9998,
       "check-local" => "disable",
       "disable-time" => 0),
   "server3" => (
       "host" => "127.0.0.1",
       "port" => 9999,
       "check-local" => "disable",
       "disable-time" => 0)
   ))

Apache:

<VirtualHost your-ip:80>
   AddDefaultCharset utf-8
   ServerName www.yourdomain
   DocumentRoot /your-switchtower-root/current/public
   ErrorDocument 500 /500.html
   ErrorDocument 404 /404.html
   # handle all requests throug SCGI
   SCGIMount / 127.0.0.1:9999
   # matches locations with a dot following at least one more characters,
   # that is, things like   *,html, *.css, *.js, which should be delivered
   # directly from the filesystem
   <LocationMatch \..+$>
       # don't handle those with SCGI
       SCGIHandler Off
   </LocationMatch>
   <Directory /your-switchtower-root/current/public/>
       Options +FollowSymLinks
       Order allow,deny
       allow from all
   </Directory>
</VirtualHost>

Changes from version 0.9.0

The library should now run on Windows, though there may be issues shutting it down.

Changes from version 0.8.0

You can pass a socket to SCGI::Processor.new via settings
You can have a socket created for you in new if you pass settings and settings
You can pass an existing logger to new via settings
Passing a socket to listen is now optional, if you passed a socket or had one created in new
Improved RDoc for new
Most SCGI::Processor methods are now private
SCGI::Processor is easier to subclass because it will use preexisting instance variables

Changes from version 0.7.0

Command line tool is now in a seperate gem called ruby-style
You now must pass a socket to SCGI::Processor#listen
SCGI::Processor’s @log and @maxconns now have defaults
SCGI::Processor’s @host and @port are no longer used

Changes from SCGI Rails Runner by Zed Shaw

Single-port clustering is back
scgi_ctrl is fully configurable on the command line
Clustering and processing are now built into scgi_ctrl
DRb, Win32, and throttling are no longer supported
Soft reconfiguration has changed (no SIGUSR1)
Restarting via SIGHUP is only supported in supervise mode
The only commands available to scgi_ctrl are start, stop, and restart

FAQ

Q: Have you been living under a rock for the last two years? Mongrel/Nginx is the new hotness!

A: Well, aren’t you snotty. You can certainly use Mongrel if you want. The memory/performance differences are small, and it is probably better maintained. ruby-scgi is a simpler version of SCGI Rails Runner, and may be useful for certain legacy setups. Also, it works well and it’s been working for me for the last few years.