Check the FQDN is valid and resolvable

mass_dns_check.rb

#!/usr/bin/env ruby

# Google Public DNS
#DNS = %w( 8.8.8.8 8.8.4.4 )

# (Recommended) Google Public DNS, Dnsadvantage, OpenDNS, NortonDNS, Level 3
DNS = %w( 8.8.8.8 8.8.4.4 156.154.70.1 156.154.71.1 208.67.222.222 208.67.220.220 198.153.192.1 198.153.194.1 4.2.2.1 4.2.2.2 4.2.2.3 4.2.2.4 4.2.2.5 4.2.2.6 )

WAITMAX = 5000 # ms

unless ARGV[0]
  puts <<README
Usage:
$ ./#{File.basename(__FILE__)} filename

Check if the FQDN is valid and can be name resolution.
File contents must be separated by newlines.
README
  exit
end

file = File.expand_path ARGV[0]
if ! File.exist? ARGV[0]
  puts "File (#{file}) is not found."
  exit
end

fqdn = []
begin
  f = open file
  f.each {|l| fqdn << l.strip }
  f.close
rescue
  puts "Failed to read file (#{file})."
  exit
end

nxdomain = []
noerror  = []
servfail = []
other    = []

threads = []

fqdn.each {|h|
  threads << Thread.new(h) {|h|
    sleep(rand(WAITMAX).to_f / 1000)

    s = DNS.at(rand(DNS.size))
    r = `dig #{h} @#{s}`.strip
    o = "#{h} [#{s}]"

    if r.include? 'status: NOERROR'
      noerror << o
    elsif r.include? 'status: NXDOMAIN'
      nxdomain << o
    elsif r.include? 'status: SERVFAIL'
      servfail << o
    else
      r = r.gsub(/[\n\r;<>]/, ' ')
      r = r.gsub(/\s+/, ' ')

      other << "#{o}\n(#{r})"
    end
  }
}

max = threads.size - 1
for i in 0..max
  threads[i].join
end

noerror = [] # prevent display noerror (too verbose)

v = false
if ! noerror.empty?
  puts if v
  puts '## NOERROR ##'
  puts noerror
  v = true
end
if ! nxdomain.empty?
  puts if v
  puts '## NXDOMAIN ##'
  puts nxdomain
  v = true
end
if ! servfail.empty?
  puts if v
  puts '## SERVFAIL ##'
  puts servfail
  v = true
end
if ! other.empty?
  puts if v
  puts '## OTHERWISE ##'
  puts other
  v = true
end