Ruby: Parse API Response - ruby

Question

I am trying to geht this script to run: http://dysinger.net/2008/10/13/using-amazon-ec2-metadata-as-a-simple-dns but dosnt work because it is using an old amazon sdk version, i rewrote it to use the new one:
#!/usr/bin/env ruby
require "rubygems"
require "aws-sdk"
%w(optparse rubygems aws-sdk resolv pp).each {|l| require l}
options = {}
parser = OptionParser.new do |p|
p.banner = "Usage: hosts [options]"
p.on("-a", "--access-key USER", "The user's AWS access key ID.") do |aki|
options[:access_key_id] = aki
end
p.on("-s",
"--secret-key PASSWORD",
"The user's AWS secret access key.") do |sak|
options[:secret_access_key] = sak
end
p.on_tail("-h", "--help", "Show this message") {
puts(p)
exit
}
p.parse!(ARGV) rescue puts(p)
end
if options.key?(:access_key_id) and options.key?(:secret_access_key)
puts "127.0.0.1 localhost"
AWS.config(options)
AWS::EC2.new(options)
answer = AWS::EC2::Client.new.describe_instances
answer.reservationSet.item.each do |r|
r.instancesSet.item.each do |i|
if i.instanceState.name =~ /running/
puts(Resolv::DNS.new.getaddress(i.privateDnsName).to_s +
" #{i.keyName}.ec2 #{i.keyName}")
end
end
end
else
puts(parser)
exit(1)
end
What this should do is outputing a new /etc/hosts file with my ec2 instances in it.
And i get a response =D, but answer is a hash and therefore i get the
error undefined method `reservationSet' for #<Hash:0x7f7573b27880>.
And this is my problem, since i dont know Ruby at all ( All I was doing was reading Amazon Documentation and playing around so i get an answer ). Somehow in the original example this seemed to work. I suppose that back then, the API did not return a hash, anyway...how can i iterate through a hash like above, to get this to work?

Answer 1

This code may help you:
answer = AWS::EC2::Client.new.describe_instances
reservations = answer[:reservation_set]
reservations.each do |reservation|
instances = reservation[:instances_set]
instances.each do |instance|
if instance[:instance_state][:name] == "running"
private_dns_name = instance[:private_dns_name]
key_name = instance[:key_name]
address = Resolv::DNS.new.getaddress(private_dns_name)
puts "{address} #{key_name}.ec2 #{key_name}"
end
end
end
Generally change your code from using methods with names e.g. item.fooBarBaz to using a hash e.g. item[:foo_bar_baz]
When you're learning Ruby the "pp" command is very useful for pretty-printing variables as you go, such as:
pp reservations
pp instances
pp private_dns_name