Michael Bensoussan

Register to an image loaded event with jQuery

2010-07-26T00:00:00-04:00

Register to an image loaded event with jQuery

26 July 2010

I recently was working on a lightbox where I needed to display a remote image and recenter the lighbox once the image is loaded.
This may seems pretty simple but it took me some time to discover that jQuery does the job via the load method.
As soon as the image has been loaded, the handler is called.

  $("#image_id").load(function(){
    // stuff to do after the image is loaded
  });

Creating an activity feed with rails, AR and observers

2010-05-23T00:00:00-04:00

Creating an activity feed with rails, AR and observers

23 May 2010

I recently had to build an activity feed at letitcast.com.
It’s a common thing to do, but I thought I might mention how I did it, and see if anyone else has suggestions/improvements.

We wanted to display to our actors new parts that correspond to their profile, new feedbacks and views of their auditions , recent comments …

So, I first created a model “activity”, here’s the migration :

  class CreateActivities < ActiveRecord::Migration
    def self.up
      create_table :activities do |t|
        t.integer :user_id, :null => false
        t.integer :activity_type, :null => false
        t.integer :target_id, :null => false
        t.string  :target_type, :null => false
        t.timestamps
      end

       add_index :activities, [:target_id, :target_type]
       add_index :activities, :user_id

    end

    def self.down
      drop_table :activities
    end
  end

As you can see it’s a polymorphic model, so the activity can be related to any active record model.

Here’s the model :

  class Activity < ActiveRecord::Base
    belongs_to :user
    belongs_to :target, :polymorphic => true
  
    default_scope :order => 'activities.created_at DESC', :limit => 10
  
    AUDITION_POSTED           = 1 #target --> model audition
    AUDITION_FEEDBACK_UPDATED = 2 #target --> model audition
    AUDITION_VIEWED           = 3 #target --> model video
    NEW_PART                  = 4 #target --> model part
  
    class << self
      def add(user, activity_type, target)
        return false if user.blank? or activity_type.blank? or target.blank?
        activity = Activity.new(:user => user, :activity_type => activity_type, :target => target)
        activity.save!
      end
    end
  
  end

At the beginning the activity types were mapped in an other database but it was a bit overkill and was reducing the performance a lot so I just added them into the model (AUDITION_POSTED, AUDITION_FEEDBACK_UPDATED, …)

I decided to create the activities via observers, example :

  class AuditionObserver < ActiveRecord::Observer

    # ACTIVITY OBSERVER : new audition posted
    def after_create(audition)
      if audition.actor
        Activity.add(audition.actor.user, Activity::AUDITION_POSTED, audition)
      end
    end

  end

So now, I can add any event via a simple variable in the activity model and an observer.

It was working really well but there were some performance issues with some events that required a lot of inserts in the activity model.
I first decided to execute this observer in a delayed job but after some research I ended up with a fast way to insert a batch of activities, here’s the method :

 def batch_add(users, activity_type, target)
    return false if users.blank? or activity_type.blank? or target.blank?
    inserts = []
    users.each {|user| inserts.push "('#{user.id}', '#{activity_type}', '#{target.id}', '#{target.class}', UTC_TIMESTAMP())" }

    sql = "INSERT INTO activities (`user_id`, `activity_type`, `target_id`, `target_type`, `created_at`) VALUES #{inserts.join(", ")}"
    ActiveRecord::Base.connection.execute sql
  end

To retrieve the activities :

  @user.activities

By default you’ll get 10 activities order by most recents.
If you want to change this behavior, just change the default_scope.

We’re also in the process of grouping the user activities to display them in a nice view, so there will maybe be a part II :-)

Optional local in partial that doesn't break

2010-05-22T00:00:00-04:00

Optional local in partial that doesn’t break

22 May 2010

If you have a partial called with or without local parameters, example :

= render :partial => 'user/new'
= render :partial => 'user/new', :locals => { :show_ad => true }

And you don’t want the partial to break when the local isn’t assigned, you can access it through the local_assigns variable :

- if local_assigns[:show_ad]
  = render :partial => "ad"

"can't find headers file for ruby" while installing gems

2010-01-02T00:00:00-05:00

“can’t find headers file for ruby” while installing gems

02 January 2010

I just reinstall my old MacBook and had a problem I got each time I install a Mac OSX.

$ sudo gem install RedCloth
Password:
Building native extensions.  This could take a while...
ERROR:  Error installing RedCloth:
	ERROR: Failed to build gem native extension.

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
can't find header files for ruby.


Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/RedCloth-4.2.2 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/RedCloth-4.2.2/ext/redcloth_scan/gem_make.out

And the solution is really simple but I always forget it :

Install Xcode here.

Mac OSX tricks 1 : cannot empty your trash ? use lsof

2010-01-01T00:00:00-05:00

Mac OSX tricks 1 : cannot empty your trash ? use lsof

01 January 2010

So you want to empty you Trash but you have this below message saying that the file is already in use.

You click continue but the file isn’t deleted.

In this case, the problem is that the file is a dmg and is mounted.
You just have to unmount the image to be able to delete it permanently.

But in some cases you don’t really know what’s the process currently using your file(s).

Here’s come lsof !
If you open the lsof man, you’ll read : lsof – list open files
So if you just type lsof without any arguments, it lists all open files by all processes.

lsof also take one or several files in argument so it can list all the processes using this file(s).

$ lsof .Trash/Spotify.dmg
COMMAND    PID USER   FD   TYPE DEVICE SIZE/OFF   NODE NAME
diskimage 1842 mike    3r   REG   14,2  3286498 928605 .Trash/Spotify.dmg

Here you can identify diskimage as the process using our file.
Now that you know the file is mounted, you can unmount it using the finder or the command line :

$ diskutil unmount /Volumes/Spotify

Or simply kill the process (in this case it will unmount it) by using the PID nicely given by lsof :

$ kill -9 1842

You can now empty your Trash.

Using Nginx as a load balancer

2009-12-30T00:00:00-05:00

Using Nginx as a load balancer

30 December 2009

Here’s a look at how nginx does basic load balancing :

upstream  yoursite  {
   server   yoursite1.yoursite.com;
   server   yoursite2.yoursite.com;
}

server {
   server_name www.yoursite.com;
   location / {
      proxy_pass  http://yoursite;
   }
}

This configuration will send 50% of the requests for www.yoursite.com to yoursite1.yoursite.com and the other 50% to yoursite2.yoursite.com.

ip_hash

You can specify the ip_hash directive that guarantees the client request will always be transferred to the same server.
If this server is considered inoperative, then the request of this client will be transferred to another server.

upstream  yoursite  {
   ip_hash;
   server   yoursite1.yoursite.com;
   server   yoursite2.yoursite.com;
}

down

If one of the servers must be removed for some time, you must mark that server as down.

upstream  yoursite  {
   ip_hash;
   server   yoursite1.yoursite.com down;
   server   yoursite2.yoursite.com;
}

weight

If you add a weight tag onto the end of the server definition you can modify the percentages of the requests send to the servers.
When there’s no weight set, the weight is equal to one.

upstream  yoursite  {
   server   yoursite1.yoursite.com weight=4;
   server   yoursite2.yoursite.com;
}

This configuration will send 80% of the requests to yoursite1.yoursite.com and the other 20% to yoursite2.yoursite.com.

note: It’s not possible to combine ip_hash and weight directives.

max_fails and fail_timeout

max_fails is a directive defining the number of unsuccessful attempts in the time period defined by fail_timeout before the server is considered inoperative. If not set, the number of attempts is one. A value of 0 turns off this check.
If fail_timeout is not set the time is 10 seconds.

upstream  yoursite  {
   server   yoursite1.yoursite.com;
   server   yoursite2.yoursite.com max_fails=3  fail_timeout=30s;
}

In this configuration nginx will consider yoursite2.yoursite.com as inoperative if a request fails 3 times with a 30s timeout.

backup

If the non-backup servers are all down or busy, the server(s) with the backup directive will be used.

upstream  yoursite  {
   server   yoursite1.yoursite.com max_fails=3;
   server   yoursite2.yoursite.com max_fails=3;
   server   yoursite3.yoursite.com backup;
}

This configuration will send 50% of the requests for www.yoursite.com to yoursite1.yoursite.com and the other 50% to yoursite2.yoursite.com.
If yoursite1.yoursite.com and yoursite2.yoursite.com both fails 3 times the requests will be send to yoursite3.yoursite.com.

Installing Jekyll and Pygments on ArchLinux

2009-12-23T00:00:00-05:00

Installing Jekyll and Pygments on ArchLinux

23 December 2009

Jekyll is a simple, blog aware, static site generator. I use it for this blog and the cool part about it is that is very simple and easy to use and there’s already plenty of websites using it.
I forked jtoy.net and was ready to blog in about an hour.

I didn’t use ruby1.9 but 1.8.7 because of some issues with pygments.

First if you don’t have ruby, let’s install it.
Remove the “ruby” package, so that it doesn’t mess up, and retrieve and build the packages with any way you’re comfortable with,

$ pacman -R ruby
$ yaourt -S ruby1.8
$ yaourt -S rubygems1.8

# ruby1.8 installs ruby-1.8 executable. link it to "ruby":
$ cd /usr/bin
$ ln ruby-1.8 ruby -s

If you need syntax highlighting, you need python and pygments :

$ pacman -S python

download the last version of easy_install (ruby gems equivalent for python) and install pygments :

$ wget http://pypi.python.org/packages/2.6/s/setuptools/setuptools-0.6c11-py2.6.egg
$ sudo sh setuptools-0.6c11-py2.6.eg
$ easy_install Pygments

Install Jekyll :

$ sudo gem install jekyll

Next, if you want the “Related posts” feature, you’ll need the the Ruby GSL package.
I first tried to install it via yaourt but it didn’t work (conflicts with rubygems), next I try do download the last version (1.10.3) but it didn’t work as well … So I took the last version from the SVN :

$ svn checkout svn://rubyforge.org/var/svn/rb-gsl
$ cd rb-gsl/trunk/rb-gsl
$ ruby setup.rb config
$ ruby setup.rb setup
$ sudo ruby setup.rb install

Finally, this is how I run Jekyll:

$ jekyll --pygments --lsi

To preview the website you can specify the option —server

Monitoring Apache with Bluepill

2009-12-22T00:00:00-05:00

Monitoring Apache with Bluepill

22 December 2009

I always used god to monitor my processes. god is working fine, has a lot of features and is very easy to use, but has some serious memory leaks. To handle this problem I usually set-up a cron to restart god every day.

Recently I read an article about a new process monitoring tool called bluepill based on EventMachine. The DSL looks simple and comes memory-leaks-less.

In this article I’ll cover how to install it and monitor apache.

First let’s grab it :

$ sudo gem install bluepill

Next, we need to configure the syslogger to log the local6 facility used by bluepill.

If your syslogger is syslog, add a line to /etc/syslog.conf :

local6.*          /var/log/bluepill.log

If it’s syslog-ng, add ths to /etc/syslog-ng.conf :

filter f_local6 { facility(local6); };
destination d_local6 { file("/var/log/bluepill.log"); };

log { source(src); filter(f_local6); destination(d_local6); };

You’ll also want to add /var/log/bluepill.log to /etc/logrotate.d/syslog so that it gets rotated.

Next restart your syslogger, for syslog-ng :

$ sudo /etc/rc.d/syslog-ng restart

And finally create the /var/bluepill directory for bluepill to store its pid and sock files.

Finally let’s create our bluepill script to monitor apache in apache-monitor.pill :

Bluepill.application("httpd") do |app|
	app.process("httpd") do |process|
		process.pid_file = "/var/run/httpd/httpd.pid"
		process.start_command = "apachectl start"
		process.stop_command = "apachectl stop"
		process.restart_command = "apachectl restart"
		process.start_grace_time = 10.seconds
		process.stop_grace_time = 10.seconds
		process.restart_grace_time = 10.seconds
	end
end

This simple script just checks if apache is up and if not reboot it.
You can try it by :

$ sudo bluepill load apache-monitor.pill

You can try to kill your httpd processes and you’ll see the magic happens, bluepill will restart them.

Bluepill comes with some great features to monitor your memory and cpu, so you can add to your script :

process.checks :cpu_usage, :every => 10.seconds, :below => 5, :times => 3
process.checks :mem_usage, :every => 10.seconds, :below => 100.megabytes, :times => [3,5]

The first line checks every 10 seconds to make sure the cpu usage of this process is below 5 percent; 3 failed checks results in a restart.
The second line checks every 10 seconds to make sure memory usage is below 100MB; 3 out of 5 failed attempts results in a restart.

If you want your bluepill daemon to run at boot, just add a line to /etc/rc.local :

$ sudo bluepill load /full/path/to/your/script/apache-monitor.pill

Introduction

2009-12-22T00:00:00-05:00

Introduction

22 December 2009

I always wanted to create a technical blog, but never took the time to do it.
Recently, I wanted to play with Jekyll, a simple static site generator and just bought a VPS instance on linode. So I made the jump and create this blog from a github fork.

I’m mainly doing some ruby stuff but buying this server was a way to hack a bit with archlinux and learn some basic sysadmin. I hope some of you will find something interesting here, otherwise you can just make fun of my English.