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Kirk: a JRuby Rack server based on Jetty

Kirk is a wrapper around Jetty that hides all of the insanity and wraps your Rack application in a loving embrace. Also, Kirk is probably the least HTTP retarded ruby rack server out there.

TL;DR

gem install kirk
rackup -s Kirk config.ru

Features

Here is a brief highlight of some of the features available.

  • 0 Downtime deploys: Deploy new versions of your rack application without losing a single request. This happens atomically so it will work even under heavy load. Also, if the redeploy fails for some reason (the application fails to boot), then the previous application remains live.

  • Request body streaming: Have a large request body to handle? Why wait until receiving the entire thing before starting the work?

  • HTTP goodness: Transfer-Encoding: chunked, Content-Encoding: gzip (and deflate) support on the request.

  • Concurrency: As it turns out, it's nice to not block your entire application while waiting for an HTTP request to finish. It's also nice to be able to handle more than 50 concurrent requests without burning over 5GB of RAM. Sure, RAM is cheap, but using Kirk is cheaper ;)

  • Run on the JVM: I, for one, am a fan of having a predictable GC, a JIT compiler, and other goodness.

Getting Started

To take advantage of the zero downtime redeploy features, you will need to create a configuration file that describes to Kirk how to start and watch the rack application. You can create the file anywhere. For example, let's say that we are going to put the following configuration file at /path/to/Kirkfile.

# Set the log level to ALL.
log :level => :all

rack "/path/to/my/rackup/config.ru" do
  # Set the host and / or port that this rack application will
  # be available on. This defaults to "0.0.0.0:9090"
  listen 80

  # Set the host names that this rack application wll be available
  # on. This defaults to "*"
  hosts "example.com", "*.example.org"

  # Set arbitrary ENV variables
  env :RAILS_ENV => "production"

  # Set the file that controls the redeploys. This is relative to
  # the applications root (the directory that the rackup file lives
  # in). Touch this file to redepoy the application.
  watch "REVISION"
end

rack "/path/to/another/rackup/config.ru" do
  # More settings here
end

Once you have Kirk configured, start it up with the following command:

kirk -c /path/to/Kirkfile

... and you're off.

Redeploying

As showed above, one way to trigger a redeploy is to specify a magic file to watch and then touch it. While this is simple, it doesn't give you any insight into the process of the redeploy. If the redeploy fails, there is no feedback.

Another way to deploy is by running kirk redeploy -R /path/to/app/config.ru

$ kirk redeploy -R /path/to/app/config.ru
Waiting for response...
Redeploying application...
Redeploy complete.

... that was easy.

Daemonizing Kirk

Use your OS features. For example, write an upstart script or use start-stop-daemon.

Logging to a file or syslog

Kirk just dumps logs to stdout, so just pipe Kirk to logger.

Kirk::Client - For all your HTTP needs

Need to make one off HTTP requests?

resp = Kirk::Client.get 'http://www.google.com'
puts resp.body

That was cool, but I wouldn't recommending doing that in your Rails app. Following is the more advanced API.

First, create an instance of Kirk::Client. This object is thread-safe (or at least it should be) and will manage your connection pool. Any connection that can be kept alive will be stored by Kirk::Client and reused on subsequent requests.

MY_CLIENT = Kirk::Client.new

Next, you'll want to implement a class to handle the responses. Just implement any method that you want to use.

class MyHandler
  # Handle exceptions
  def on_exception(exception)
  end

  # The request to the server has finished, but the
  # server has not responded yet.
  def on_request_complete
  end

  # The server has finished sending the response header
  def on_response_head(response)
    puts "STATUS: #{response.status}"
    response.headers.each do |name, val|
      puts "  #{name}: #{val}"
    end
  end

  # The server is sending the response body. This method could
  # be called multiple times depending on the number of chunks
  # that are received.
  #
  # Also, if this method is implemented, the response body won't
  # be buffered in the response object.
  def on_response_body(response, chunk)
    # response.body == nil
    print chunk
  end

  def on_response_complete(response)
    puts "The response has been received"
  end
end

Now, you can start making the requests.

MY_CLIENT.group do |g|

  # All of these requests will happen in parallel.
  g.get  'http://www.google.com',  MyHandler.new
  g.post 'http://www.twitter.com', MyHandler.new, "Some request body"
  g.get  'http://www.amazon.com', nil, nil, 'X-Custom-Header' => 'Blah'

  # The group will block until all of the requests are completed.
end

Hopefully that is enough to get started.

Caveats

This is still a pretty new project and a lot of settings that should be abstracted are still hardcoded in the source.

  • Kirk requires JRuby 1.6.0 RC 1 or greater. This is due to a JRuby bug that was fixed in the 1.6 branch but never backported to older versions of JRuby. Crazy stuff happens without the bug fix.

  • The JDBC drivers will keep connections open unless they are explicitly cleaned up, something which Rack applications do not do. A future release of the jdbc ruby drivers will correctly clean up after the JDBC garbage, but for now, you will have to manually do it. If you are running a Rails app, add the following to the config.ru file:

    at_exit { ActiveRecord::Base.clear_all_connections! }

Getting Help

Ping me (carllerche) on Freenode in #carlhuda

Reporting Bugs

Just post them to the Github repository's issue tracker.