vi /etc/apt/sources.list

add the repositories
deb http://us.archive.ubuntu.com/ubuntu/ hardy main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ hardy main restricted

then run
sudo apt-get update
sudo apt-get install php5

This tried to install and upgrade a lot of packages including apache. I really needed php 5.2 and since the server is a development server, I accepted all the changes.

You need to get tilt 0.3 from gemcutter.org.
sudo gem install --no-ri --no-rdoc tilt --source=http://gemcutter.org

To get the latest Sinatra
cd myapp
git clone git://github.com/sinatra/sinatra.git

and add it to the LOAD_PATH
$LOAD_PATH.unshift File.dirname(__FILE__) + '/sinatra/lib'

To set the dash as the ‘trim’ character, add
set :erb, :trim => '-'

If you’re using sinatra, the syntax is similar to rails. Check out the rack-flash page here.

I added rack-flash to my sinatra app. Check out the git commit. Since rack-flash uses the session, don’t forget to add Rack::Session::Cookie.

Watch the video of Jon Crosby’s talk In a World of Middleware, Who Needs Monolithic Applications? at Mountain West Ruby Conference 2009 for more on rack middleware.

If you want to learn sinatra, the README will quickly show you what you can do with this framework.

I haven’t used Datamapper so I took this opportunity to learn it as well. You just need to require ‘dm-core’. That’s it. If you want to put your models on a separate file, you have to require that as well. If you’re using Rails, you’re probably used to models being available right away. I also used haml instead of erb.

The code is available at github. The Sinatra book has a list of Real World Applications. I looked at the seinfeld app as a basis for the structure.

There is more I want to learn in Sinatra. Since it uses Rack, I want to try using the different Rack Middleware available.

Paperclip is a library for ActiveRecord used for file attachment. The most common use is for uploading images. It can optionally create thumbnails when you upload images. Paperclip requires ImageMagick for resizing images but it doesn’t require any Ruby libraries like RMagick or MiniMagick.

You can install paperclip as a gem or as a plugin. The paperclip gem needs right_aws, mocha, and shoulda.
gem install right_aws
gem install mocha
gem install thoughtbot-shoulda --source=http://gems.github.com
gem install thoughtbot-paperclip --source=http://gems.github.com

To install the plugin, run ./script/plugin install git://github.com/thoughtbot/paperclip.git.

Let’s say you have a User model and you want to add an avatar. On the users table, you need to add avatar_file_name.

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :login
      t.string :avatar_file_name
    end
  end

  def self.down
    drop_table :users
  end
end

On user.rb, add has_attached_file

class User < ActiveRecord::Base
  has_attached_file :avatar
end

You just need to set avatar to an uploaded file and paperclip will handle the rest. On app/views/users/new.html.erb

  <% form_for :user, @user, :url => users_path, :html => { :multipart => true } do |form| %>
    <%= form.text_field :login %> <br />
    <%= form.file_field :avatar %> <br />
    <%= submit_tag 'Save' %>
  <% end %>

:multipart => true is needed when uploading files. Then on app/controllers/users_controller.rb

  def new
    @user = User.new
  end

  def create
    @user = User.create(params[:user])
  end

@user.avatar.url will give you the url of the uploaded image. That’s all the code you need to use paperclip. There are more options for creating thumbnails, validating the model, and post-processing.

The uploaded files will be saved on RAILS_ROOT/public/system/:attachment/:id/:style/:basename.:extension. On my computer the file is saved on RAILS_ROOT/public/system/avatars/1/original/image.jpg.

As you can see, the default style is original. To add more ’styles’,

class User < ActiveRecord::Base
  has_attached_file :avatar, :styles => { :medium => "300x300>", :thumb => "100x100>" }
end

When you upload the image, paperclip will save the original image, and resize the image to medium and thumb. On RAILS_ROOT/public/system/avatars/2, you will see the directories original, medium and thumb.

To get the medium and thumb images, you will use @user.avatar.url(:medium) and @user.avatar.url(:thumb).

On the users table, you can also add avatar_content_type (string), avatar_file_size (integer), and avatar_updated_at (datetime). These fields will be populated by paperclip automatically.

I will discuss validation and other post-processing options on my next post.

Nothing changes though on how you use sessions on Rails. On your Rails app, you’ll have something like

session[:user] = some_user_id

Let’s see how we can access the same session on a Rack application. You can read about Rack here.

Rack handles session using Rack::Session::Cookie. Create a file config.ru

use Rack::Session::Cookie, :key => '_railssession_session', :domain => 'railssession.labs.admoolabs.com'
run Proc.new {|env| [200, {"Content-Type" => "text/html"}, "Rack session 'user' has a value of #{env['rack.session'][:user] || 'nil'}."]}

The key should be the same key that you used on config/environment.rb on your Rails app.

Check out the demo. Set session[:user] on the Rails app, then view the session on the Rack app.

I will show you how to use capistrano for deploying a Rails application. The goal is to deploy an application by running one command – “cap deploy”. This should update your code from Subversion, and restart your server.

I assume that you have a rails setup on your server. I use the nginx web server, mongrels and mongrel_cluster.

To install capistrano

gem install capistrano

To start using capistrano on your Rails application,

cd RAILS_ROOT
capify .

You should see two files – Capfile and config/deploy.rb. Capistrano looks for Capfile when you run any capistrano commands. The default Capfile loads config/deploy.rb. deploy.rb contains the settings for your application.

We will deploy the Rails app “Hello Labs”. This can be found on our repository. Let’s edit deploy.rb.

Set the user and runner that will run the commands on your server.

set :user, "crigor"
set :runner, "crigor"

Set the application name

set :application, "hellolabs"

Set the scm and repository

set :scm, :subversion
set :repository, "http://labs.svn.admoolabs.com/hellolabs/trunk"

The default :scm is actually :subversion but I like to put it anyway.

Set the directory on the target server where you will deploy the application.

set :deploy_to, "/var/www/#{application}"

application is “hellolabs” which you set earlier. The deploy_to directory, which I’ll call DEPLOY_ROOT, is /var/www/hellolabs. You should create this directory on the target server. On Ubuntu, I set the group to www-data so mongrel has access to it.

Set the servers.

role :app, 'hello.labs.admoolabs.com'
role :web, 'hello.labs.admoolabs.com'
role :db, 'hello.labs.admoolabs.com', :primary => true

You can also use the IP address instead of the domain.

If nginx, mongrel, and mysql are all on the same server, put the same domain or IP address.

Now we will run our first capistrano task. Make sure /var/www/hellolabs exists on your server. On the RAILS_ROOT, run

cap deploy:setup

This will create the releases directory and shared directory under the hellolabs directory on the remote server. If you get a permission error, make sure the user you specified has access to /var/www/hellolabs.

Capistrano will ask for you server password. If you don’t want to enter your password every time you run a capistrano task, you can add

set :password, "mypassword"

Check if we have met the dependencies.

cap deploy:check

The output, if deploy:check is successful, looks like this.

Before we deploy the app, we define the deploy:restart task. By default capistrano runs /var/www/hellolabs/current/script/process/reaper. I use mongrel and mongrel_cluster so let’s add

namespace :deploy do
  desc "Restart the mongrels"
  task :restart do
    run "mongrel_rails cluster::restart -C #{shared_path}/config/mongrel_cluster.yml"
  end
end

Create the /var/www/hellolabs/shared/config directory and add mongrel_cluster.yml. We also need to add database.yml. I don’t commit database.yml in my repository since it contains the database password.

We have to symlink mongrel_cluster.yml and database.yml every time we deploy.

after "deploy:update_code", "deploy:symlink_configs"
namespace :deploy do
  desc "Symlink the config files."
  task :symlink_configs do
    run "ln -nfs #{shared_path}/config/database.yml #{latest_release}/config/database.yml"
    run "ln -nfs #{shared_path}/config/mongrel_cluster.yml #{latest_release}/config/mongrel_cluster.yml"
  end
end

We’re now ready to deploy our application.

cap deploy

If you see something similar to this, your app has been deployed.

The releases directory will contain directories with the timestamp as the name like 20081017125102 and 20081017132929. These directories will contain the rails application.

Below, you can see that current is a symlink to 20081017132929. /var/www/hellolabs/current is your RAILS_ROOT.

Check the URL of your app. http://hello.labs.admoolabs.com

If you need a username and password to checkout your repostory, add

set :scm_username, "username"
set :scm_password, "password"

To get the list of capistrano tasks available, run cap -T.

For more information, check the capistrano website.

Here is the complete deploy.rb

set :user, "crigor"
set :runner, "crigor"

set :application, "hellolabs"
set :scm, :subversion
set :repository, "http://labs.svn.admoolabs.com/hellolabs/trunk"
set :deploy_to, "/var/www/#{application}"

role :app, 'hello.labs.admoolabs.com'
role :web, 'hello.labs.admoolabs.com'
role :db, 'hello.labs.admoolabs.com', :primary => true

after "deploy:update_code", "deploy:symlink_configs"
namespace :deploy do
  desc "Symlink the config files."
  task :symlink_configs do
    run "ln -nfs #{shared_path}/config/database.yml #{latest_release}/config/database.yml"
    run "ln -nfs #{shared_path}/config/mongrel_cluster.yml #{latest_release}/config/mongrel_cluster.yml"
  end

  desc "Restart the mongrels"
  task :restart do
    run "mongrel_rails cluster::restart -C #{shared_path}/config/mongrel_cluster.yml"
  end
end

PNOI is an individual programming contest for high school students. I’m a judge (and 4 others) at this contest.

Click here for the details.