zk_monitor.rb

require 'zk'
require 'msgpack'

class Events
  def initialize
    @zk = ZK.new
    @root_node = '/fuzz'
    @node_metadata=MessagePack.pack 'required_workers'=>3
    if @zk.stat( @root_node ).exists?
      @zk.set @root_node, @node_metadata
    else
      @zk.create @root_node, @node_metadata
    end
  end

  def run
    begin
      @zk.register(@root_node) do |event|
        case event
        when node_changed?
          # fetch the latest data and re-set watch
          data = @zk.get(@root_node, watch: true).first
          puts "Metadata was changed: #{MessagePack.unpack(data)}"
        when node_children?
          # Get data, reset watch on the root node (NOT the child)
          puts "Children changed: #{@zk.children(@root_node, watch: true)}"
        end
      end
    ensure
      @zk.close!
    end
  end
end

Events.new.run