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Deploy Ruby as a Gem

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Background

I was looking at git-deploy and it looks really awesome. But it got me thinking: We have tools like bundler and rack that can handle gem versioning and dependencies, and creating clean interfaces for web applications. Why can’t we use those tools for deploying our own code?

I think ruby gems are a great way of packaging code up, and that any code you write should become a gem if it needs to be re-used. Gems are pretty easy to write, and they automatically help you package and version your code.

I also think we should be doing more version-based deploys of code. Even if it’s just a git tag. But it’s better if it’s actually an application version.

So, I stumbled across Running Sinatra inside a Ruby Gem by Florian Hanke, and I really liked it, but I wanted to take it one step further: deploying.

Application Setup

The first thing we have to do is setup our application:

bundle gem awesome_site

That will make a gem scaffold inside the awesome_site folder for a gem called AwesomeSite. Next, in awesome_site.gemspec add:

gem.add_dependency 'sinatra', '1.3.2'

Also, update the gem.description and gem.summary.

Next, we’re going to add a config.ru, which will help us test our application in development:

require 'rubygems'
require 'bundler'
Bundler.setup
require 'awesome_site'
run AwesomeSite::App

So, we need to setup AwesomeSite::App as a rack app. Edit lib/awesome_site.rb to autoload App:

module AwesomeSite
  autoload :App, 'awesome_site/app'
end

Then put this in lib/awesome_site/app.rb:

require 'sinatra'
module AwesomeSite
  class App < Sinatra::Base
    get '/' do
      'hello world!'
    end
  end
end

Note that I used autoload instead of require for App and I also didn’t require Sinatra until the app.rb file. This means that loading my gem will be fast, and that sinatra won’t have its code loaded and run until the App is needed. This will keep boot times down (like when unit testing code that doesn’t need App).

Now, you should be able to run rackup and visit the app!

The last thing we need to do is rake install to build and install the gem on our local system.

Server Setup

OK, so now that we have our great app as a gem (thanks Florian!) it’s time to setup the server. Make a new directory (to simulate the server’s application folder) outside of the awesome_site folder. I just called mine server. In this folder, make a Gemfile:

source :rubygems
source 'http://0.0.0.0:8808'
gem 'awesome_site'

This Gemfile shows how I would install awesome_site from a local gem server (by running gem server) and pull dependencies from rubygems.org. An alternative would be:

source :rubygems
gem 'awesome_site', :git => 'git://github.com/ngauthier/awesome_site.git'

That could pull the gem from github, but that’s suboptimal because you would have to also send a :ref in order to set the version, which would be a pain in the next section.

A third option would be to build the gem locally and scp it to the server and install, but that doesn’t use all the fun bundler stuff!

You can use geminabox to run your own gem server that you can push gems too.

OK, now we need a config.ru file for the server. It’s the same as awesome_site’s config.ru:

require 'rubygems'
require 'bundler'
Bundler.setup
require 'awesome_site'
run AwesomeSite::App

Now, we can run bundle and rackup and we’re running our server based off our gem!

Deployment

As mentioned previously, you need to push the gem to your own gem server. That means either your gem server can check out the latest code and install the gem, or simply use geminabox to let developers push a gem. So the deployment steps would be:

  1. Update awesome_site in some way, and set AwesomeSite::VERSION to an updated number.
  2. rake build
  3. gem inabox ./pkg/awesome_site-1.0.0.gem (then enter the geminabox server url when prompted)
  4. ssh production "bundle update awesome_site && sudo restart awesome_site"

This is assuming you use upstart to manage your server process (probably my next blog topic).

Now, if you want more control, put the server code into git and manually set the version number in the gemfile. That way you can roll back to a version if you have a problem with a deploy. But, you could also reverse the commit, but bump the gem version and deploy as usual. This is a more honest representation of what happened and it means the HEAD of the code is accurate.

Disclaimer

This is theoretical. The code is available at ngauthier/awesome_site and it does work. However I have never done this on a production application, so take care if you decide to go for it. I was just curious about what the process would be like.

Happy monday!

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