Sean's Obsessions » Uncategorized

Command line geolocation

sean — Mon, 25 Jan 2010 16:59:18 +0000

A comment in a Slashdot article lead me to iploc.org, specifically Country names zone which lets you get the country for a given IP address over DNS.

I wrapped it in a bash function… throw this at the end of your .bashrc:

geo() { dig +short TXT `echo $1 | \
 awk -F. '{print $4"."$3"."$2"."$1".cc.iploc.org"}'`;}

and you can get geo information from the command line:

$ geo 204.187.154.1
"CA"

Moving from github to gemcutter for your rails app’s gems

sean — Wed, 21 Oct 2009 15:09:15 +0000

Much hoopla has been made over Github stopping their gem building service, and for people to use Gemcutter.

All the stuff I’ve read has been that gemcutter is much better for publishing Gems, and that it’s easier to find the canonical gem (instead of deciding whether fred-mygem is better than barney-mygem)

Fair enough, but what about slobs like me that haven’t had to modify gems, and just want to start using the new source for gems and to update existing apps accordingly?

Turns out, it’s pretty easy.

# Update gem to at least 1.3.5
gem update --sytem
# install gemcutter
gem install gemcutter
# update gem sources
gem tumble

If you look at ~/.gemrc, you’ll see that github has been pushed to the end:

---
:benchmark: false
:verbose: true
gem: --no-ri --no-rdoc
:update_sources: true
:sources:
- http://gemcutter.org
- http://gems.rubyforge.org/
- http://gems.github.com
:bulk_threshold: 1000
:backtrace: false

The last thing to do is to reinstall the old github gems using their new names. In environment.rb and environments/*.rb, look for your config.gem lines:

config.gem "thoughtbot-factory_girl",
       :lib     => 'factory_girl',
       :source  => 'http://gems.github.com'

Becomes:

config.gem "factory_girl"

Note that all you’re doing is taking off the owner of the gem, and then getting rid of the extra parameters.

It would be wise to first make sure that the gem is available on gemcutter. Browse to http://gemcutter.org/gems/GEMNAME, (eg http://gemcutter.org/gems/factory_girl) to see if you get an error.

Finally, run

rake gems:install

from within your app’s directory to install the new gems.

Presto! It’s easier than I thought.

How many Mongrels or FastCGI processes do I need?

sean — Wed, 19 Nov 2008 20:10:01 +0000

I’m sitting in a course on call centre design, and yesterday there was mention of Erlangs, which are a unit of measure of the volume of traffic on a telecommunications network. These Erlangs can be used to calculate how many agents a call centre needs (or, given the number of agents, what service level can be expected)

The Erlang C model is used for this, it has the built in assumption that if agents are busy then the callers queue. This is much like a Mongrel or FastCGI “agent”, with requests coming in from a front end web server.

Using the Erlang C calculator here, I can figure out how many agents I need, given the desired service level.

Arrivals: 600/minute (10 req/sec)
Service time: 0.2s
Service level: 99.9% within 0.3 s

Gives 5 agents or Mongrels. From there you can work backward with existing models to figure out how many computers you need.

With the calculator you can also fix the number of agents and figure out capacity, or blockage, or whatever.

This assumes that incoming requests follow the Poisson distribution, which I have no idea if it is true. Anyone?
Edit: Sorry, I managed to lose half the post and had to redo it.

Pushing a CakePHP app from dev to prod

sean — Tue, 06 Nov 2007 04:27:10 +0000

After more work on a CakePHP app I wanted to host it somewhere. Because this is a fairly low volume app I went with a shared hosting provider.

One problem was that I needed two different database connections, one for my development site, and one when I push it to the server. It was fairly easy to set up two different connections in app/config/database.php:
var $default = array('driver' => 'mysql', 'connect' => 'mysql_connect', 'host' => 'localhost', .... var $production = array('driver' => 'mysql', 'connect' => 'mysql_connect', 'host' => 'PRODUCTION_HOST', .....

Then within cake/app_model.php I did a check within the constructor:

class AppModel extends Model{
        function __construct($id = false, $table = null, $ds = null) {
                if ($this->isProd()) {
                        $this->useDbConfig = 'production';
                } else {
                        $this->useDbConfig = 'default';
                }
                parent::__construct();
        }
        function isProd() {
                $server = $_SERVER["HTTP_HOST"];
                if ($server ==  "DEVELOPMENT_SERVER") {
                        return false;
                } else {
                        return true;
                }
        }
}

The next order of business was to script pushing code.

#!/bin/sh
#
# FTP information
FTPHOST=xxxx.com
FTPUSER="xxxx"
FTPPASS="xxxx"
# do we cd to a dir after logging in?
FTPDIR=.
# path to base of svn
SVNDIR="http://svnserver/svn/project"
TMPDIR=/tmp/$$
#
if [ "x$1" == "x" -o "$1" == "trunk" ]; then
        SVNURL="${SVNDIR}/trunk/"
else
        SVNURL="${SVNDIR}/tags/$1/"
fi
#
echo $SVNURL
mkdir -p $TMPDIR
#
(cd $TMPDIR && svn export $SVNURL code )
#
(cat - <