Partial serverspec Rake file that loops through all nodes in a HDFS cluster automatically

Rakefile

# Two approaches to getting the list of nodes automatically.
# Some stuff re: roles from serverspec-example repository

...

def hdfsnodes()
  # Requires special access to HDFS reporting tool...
  clusterreport,nodesreport = `sudo su hdfs -c 'hdfs dfsadmin -report'`.split("\n\n-------------------------------------------------\n")
  nodesreplist=nodesreport.strip.split("\n")
  nodenamelist = nodesreplist.grep(/Name/)
  nodenamelist = nodenamelist.map! { |n| n.split(":")[0] == "Name" ? n.split(":")[1].strip : n }.sort
  nodenamelist
end

def yarnnodes()
  # All users should be able to run this
  nodes = `yarn node -list`.split("Containers\n")[1].split("\n").map! { |n|  n.split("\t")[2].split(":")[0] }
  nodes
end

...


hosts = yarnnodes() 
hosts.map! { |host|
  host.strip!
  {
    :name => host,
    :roles => roles(host),
    :tags => tags(host)
  }
}

...
  task :all => hosts.map { |h| h[:name] }
    hosts.each do |host|
      desc "Run serverspec to host #{host[:name]}"
      ServerspecTask.new(host[:name].to_sym) do |t|
        dirs = host[:roles] + [ host[:name] ]
        t.target = host[:name]
        t.tags = host[:tags]
        t.pattern = File.join('.', 'spec', '{' + dirs.join(",") + '}', '*_spec.rb')
      end
    end
  end
...
  # Per role tasks
  namespace :role do
    roles = hosts.map {|h| h[:roles]}
    roles = roles.flatten.uniq
    roles.each do |role|
      desc "Run serverspec to role #{role}"
      task "#{role}" => hosts.select { |h| h[:roles].include? role }.map {
        |h| "check:server:" + h[:name]
      }
    end
  end
end