Zookeeper leader election using Ruby

election_candidate.rb

# http://zookeeper.apache.org/doc/r3.3.4/recipes.html#sc_leaderElection
require 'rubygems'
require 'bundler/setup'
require 'zookeeper'
require 'hashie'

class ElectionCandidate
  attr_reader :zookeeper, :children, :root_path, :node_path, :my_path
  attr_accessor :logger

  def initialize zookeeper_uri, root_path, node_path, logger=Logger.new(STDOUT)
    root_path = "/#{root_path}" if root_path[0] !='/'
    @root_path, @node_path, @logger = root_path, node_path, logger
    @zookeeper = Zookeeper.new(zookeeper_uri)
    root_path_create! unless root_path_exists?
    register!
  end

  def root_path_create!
    resp = @zookeeper.create(path: @root_path, data: @root_path)
    raise "Unable to create root node" if resp[:path] == @root_path
    resp
  end

  def root_path_exists?
    Hashie::Mash.new(@zookeeper.get(path: @root_path)).stat.exists?
  end

  def register!
    raise "Already registered: #{@my_path}" if registered?
    path = "#{@root_path}/#{@node_path}"
    @logger.info "Registering node..#{path}"
    result = Hashie::Mash.new(@zookeeper.create(path: path, data: path, ephemeral: true, sequence: true))
    if result.rc == 0
      @my_path = result.path
      @logger.info([self.class, __method__].join('.')){ "My node..#{@my_path}" }
    end
  end

  def unregister!
    raise "Not registered" unless registered?
    resp = Hashie::Mash.new(@zookeeper.delete(path: @my_path))
    if resp.rc == 0
      @logger.info([self.class, __method__].join('.')){ "Succesfully unregistered #{@my_path}"}
      @my_path = nil
      return true
    end
    false
  end

  def registered?
    !@my_path.nil? && Hashie::Mash.new(@zookeeper.get(path: @my_path)).stat.exists?
  end

  def candidates
    Hashie::Mash.new(@zookeeper.get_children(path: @root_path))
  end

  def leader?
    result = candidates
    @children = result.children
    @logger.info([self.class, __method__].join('.')){"Found #{@children.size} children.."}
    @logger.debug([self.class, __method__].join('.')){@children}
    @logger.error([self.class, __method__].join('.')){"ERROR: #{result}"} if result.rc != 0

    leader = result.children.select{|c| c[/#{@node_path}/] }.sort.first
    leader_path = "#{@root_path}/#{leader}"
    @logger.debug([self.class,__method__].join('.')){"#{leader_path} is leader"}
    result.rc == 0 && result.children && @my_path == leader_path
  end
end