gistfile1.txt

# Hot deploy Rails apps (rolling restart) with Capistrano, Haproxy, and cluster of Passengers

# Capistrano config

namespace :passenger do
  task :disable_load_balancing, :roles => :app do
     run "rm -f #{current_path}/public/http-check.txt"
  end

  task :enable_load_balancing, :roles => :app do
     run "touch #{current_path}/public/http-check.txt"
  end

  task :restart, :roles => :app do
     sudo "/etc/init.d/apache2 restart"
  end
end

namespace :deploy do

  # If there is a more Capistrano-y way to do this? 
  # Using roles and somehow getting rid of the ENV[HOSTS] bit would be nice

  task :hot do
    ["assets1", "assets2"].each do |h|
      puts "Updating asset server #{h}"
      ENV['HOSTS'] = h

      update
    end
    
    ["app1", "app2", "app3"].each do |h|
      puts "Updating app server #{h}"
      ENV['HOSTS'] = h

      passenger.disable_load_balancing
      sleep 10
 
      update
      passenger.restart

      passenger.enable_load_balancing
      sleep 10
    end
  end
end

# To run...

cap deploy:hot

# Set up Haproxy to remove servers from the cluster when the http-check file is not present

backend passengers
  option httpchk GET /http-check.txt
  http-check disable-on-404
  
  server app1...
  server app2...
  server app3...


# You could also dress up the HTTP check with some extra sanity checks...

# haproxy

option httpchk GET /http-check

# rails

map.connect 'http-check', :controller => 'http_check' 

class HttpCheckController < ApplicationController
  def index
    if File.exists?("#{RAILS_ROOT}/public/http-check.txt")
      # check database connection and other stuff here..
      render :text => "OK", :layout => false
    else
      render :text => "404 Not Found : http-check does not exist", :layout => false, :status => 404
    end
  end
end

# TODO: add Nagios config - alert if an http check fails for more than X seconds