Rails - Jul 2006 - GEM-based rails application installer

I just uploaded the first version of my .gem-based Rails application installer
to Rubyforge (http://rubyforge.org/projects/rails-installer/; gem install
rails-app-installer). This is extracted from Typo 4.0, and it''s
intended to
make it easy to build user-friendly installers for Rails applications.

This isn''t intended to compete with Capistrano; it''s much
lighter-weight, and
aimed towards normal users installing applications, not production deployments
of internally-developed software.

Here''s what users need to do to install an app via this installer:

   $ sudo gem install my-app
   $ my-app install /some/path

or, without root:

   $ gem install -i ~/gems my-app
   $ ~/gems/bin/my-app install /some/path

This will build a working Typo install in /some/path, using Mongrel and
SQLite3 by default. These can both be changed via configuration settings; see
recent articles on http://scottstuff.net for details.

Here''s what you''ll need to do to add the installer to your
existing Rails app:

1.  Create a `.gem` that depends on `rails-app-installer`, `rails`, and all
    other `.gem`s that you need to have installed.
2.  Add an `executable` entry to your gemspec.  If your app is called
   `my-app`, then add `executable = [''my-app'']`.
3.  Copy the ''rails_app_installer.yml'' file from the
rails-app-installer .gem
    into a directory called ''installer'' in your application.
4.  Finally, create `bin/my-app`, using one of the examples in the
    `rails-app-installer` SVN tree as an example.

Here''s a short example `bin/my-app`:

      #!/usr/bin/env ruby

      require ''rubygems''
      require ''rails-installer''

      class AppInstaller < RailsInstaller
        application_name ''my_app''
        support_location ''my website''
        rails_version ''1.1.4''
      end

      # Installer program
      directory = ARGV[1]

      app = AppInstaller.new(directory)
      app.message_proc = Proc.new do |msg|
        STDERR.puts " #{msg}"
      end
      app.execute_command(*ARGV)

That''s all that''s needed--as long as the installer gem is
installed, this will
give you a full installer that supports installs, upgrades, db backups and
restores, and all of the other things that the Typo installer currently
provides. Adding application-specific installer subcommands is easy.
Here''s
the `sweep_cache` implementation from Typo''s installer:

      class SweepCache < RailsInstaller::Command
        help "Sweep Typo''s cache"

        def self.command(installer, *args)
          installer.sweep_cache
        end
      end

That''s all that''s needed to implement the `typo sweep_cache
/some/path`
installer command. Er, except for adding a ''sweep_cache''
method to
AppInstaller, but that''s up to you :-).