Zero-Downtime deploys with JRuby

lifecycle_listener_host.rb

def check_monitors
  @contexts.each do |c|
    #...
    c[:context] = create_takeover(c)
    Thread.new { c[:context].start }
  end
end

def create_takeover(c)
  web_app = c[:app]
  old_context = c[:context]

  context = Trinidad::Tomcat::StandardContext.new
  context.name = rand.to_s
  context.path = old_context.path
  context.doc_base = web_app.web_app_dir

  context.add_lifecycle_listener Trinidad::Tomcat::Tomcat::DefaultWebXmlListener.new

  config = Trinidad::Tomcat::ContextConfig.new
  config.default_web_xml = 'org/apache/catalina/startup/NO_DEFAULT_XML'
  context.add_lifecycle_listener config

  Trinidad::Extensions.configure_webapp_extensions(web_app.extensions, @tomcat, context)

  web_app.generate_class_loader
  context.add_lifecycle_listener(web_app.define_lifecycle)
  context.add_lifecycle_listener(Trinidad::Lifecycle::Takeover.new(c))

  old_context.parent.add_child context

  context
end

myapp-v2-knob.yml

application:
  root: /path/to/myapp.knob
web:
  context: myapp-v2/
environment:
  RAILS_ENV: production