Module: ElbPing::Resolver

Defined in:
lib/elbping/resolver.rb

Overview

Handles all DNS resolution and, more specifically, ELB node discovery

Class Method Summary collapse

Class Method Details

.find_elb_nodes(target, timeout = 5) ⇒ Object

Resolve an ELB address to a list of node IPs. Should always return a list as long as the server responded, even if it’s empty.

Arguments:

target: (string)
timeout: (fixnum)

Could raise:

  • Timeout::Error

  • ArgumentError

Raises:

  • (ArgumentError) 


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# File 'lib/elbping/resolver.rb', line 54

def self.find_elb_nodes(target, timeout=5)
  raise ArgumentError, "Could not query DNS" if target.nil?

  resp = nil

  unless target.end_with? ".elb.amazonaws.com"
    Timeout::timeout(timeout) do
      Resolv::DNS.open do |sysdns|
        resp = sysdns.getresources target, Resolv::DNS::Resource::IN::CNAME
        cname = resp[0].name.to_s if resp and resp.size > 0
        return find_elb_nodes(cname, timeout)
      end
    end
  end

  # Resolv::DNS never completes queries successfully if you pass a list
  # of nameservers to it
  nameserver = find_elb_ns(target, timeout).sample

  Timeout::timeout(timeout) do
    Resolv::DNS.open :nameserver => nameserver do |dns|
      # TODO: Exceptions
      resp = dns.getresources "all.#{target}", Resolv::DNS::Resource::IN::A
    end
  end

  if resp
    resp.select { |r| r.respond_to? "address" and r.address }.map { |r| r.address.to_s  }
  end
end

.find_elb_ns(target, timeout = 5) ⇒ Object

Find addresses authoritative DNS server

Arguments:

target: (string) ELB hostname
timeout: (fixnum) in seconds

Could raise:

  • Timeout::Error

  • ArgumentError



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# File 'lib/elbping/resolver.rb', line 19

def self.find_elb_ns(target, timeout=5)
  resp = []

  unless target.end_with? ".elb.amazonaws.com"
    raise ArgumentError, "Not an Amazon ELB hostname"
  end

  Timeout::timeout(timeout) do
    Resolv::DNS.open do |sysdns|
      resp = sysdns.getresources target, Resolv::DNS::Resource::IN::NS
    end
  end

  if resp.empty?
    parent = target.split(".")[1..-1].join('.')
    if parent.empty?
      raise ArgumentError, "Could not find Amazon nameserver for ELB"
    end
    find_elb_ns(parent, timeout)
  else
    resp.map { |ns| ns.name.to_s }
  end
end