deploy:rolling_restart

gistfile1.rb

namespace :deploy do
  
  desc "Restarts each app role one at a time, removing from load balancing during restart"
  serial_task self, :rolling_restart, :roles => :app do
    lb          = fetch(:load_balancer)
    lb_removal  = lambda { `elb-deregister-instances-from-lb #{lb} --instances #{@instance_id}` }
    lb_addition = lambda { `elb-register-instances-with-lb #{lb} --instances #{@instance_id}`   }
    
    watch       = "rails"
    port        = 8080
    heartbeat   = "/heartbeat"
    n_heartbeat = 3
 
    # Capture EC2 InstanceID by querying meta-data web service on remote instance
    run "curl -s http://169.254.169.254/2007-01-19/meta-data/instance-id" do |_,_,out| 
      @instance_id = out
    end
 
    logger.info "Removing #{@instance_id} from #{lb} load balancer..."
    lb_removal.call
    logger.info "Removed #{@instance_id} from #{lb} load balancer."
 
    logger.info "Restarting process..."
    sudo %(god restart #{watch}; sleep 2) # sleep a bit to let process fully reap (restart is async)
 
    logger.info "Waiting for port #{port} to come back up..."
    run %(while true; do echo 'waiting for port...' ; if netstat -tan | grep -q :::#{port}; then echo '#{port} up' && exit 0; fi; sleep 5; done)
 
    logger.info "Sending #{n_heartbeat} heartbeat checks to #{heartbeat}..."
    run %(for i in {1..#{n_heartbeat}}; do echo -n Attempting $i of #{n_heartbeat} requests to #{heartbeat}... && curl -s http://localhost:#{port}#{heartbeat} && echo; done)
    logger.info "Heartbeat checks successful, restart complete."
 
    logger.info "Adding #{@instance_id} to #{lb} load balancer..."
    lb_addition.call
    logger.info "Added #{@instance_id} to #{lb} load balancer."
  end
 
  desc "Custom restart behavior"
  task :restart, :roles => :app, :except => { :no_restart => true } do
    rolling_restart
  end
  
end