Update /etc/hosts based on a template usinf Knife/Chef provided info.

updhosts.rb

#Rebuild hosts file from knife node list,
require 'erb'
require 'json'
require 'ohai' #to find my own IP

def myaddress
  thissys=Ohai::System.new
	thissys.all_plugins
	myip=thissys['cloud']['private_ips'][0]
	return myip
end

#This is called in the template file by erb
def findremoteip(name=nil)
	return "#No such name" if name.nil?
	svrname=name+'.somedomain.com'
	nodes.search("name:#{svrname}") do |thisnode|
		return "#{thisnode['cloud']['private_ips'][0]} #{name} #{svrname}" if thisnode['fqdn']==svrname	
	end
	return "# No nodes entry for "+svrname
end

template='/etc/hosts.erb'
#These are used in the template.
scriptname="#{$0} #{$1}"
myip_ohai=myaddress
abort "Could not find my IP?" if myip_ohai.nil?

erb=ERB.new File.new(template).read,nil, '<>'
puts erb.result(binding)

See https://gist.github.com/4322280 for hosts.erb. Assuming you have a chef/knife env fully setup, you can run "knife exec scripts/updhosts.erb > /etc/hosts" (as root) to update the /etc/hosts file on your management work station to update IP addresses of all the managed instances in hosts to be their internal (EC2, private) addresses.
If you management work station is outside EC2, then you could change findremoteip() to return node['cloud']['public_ips'][0] - This will populate your local hosts file with the public address of the instance. Of course, this wont help if your nodes are in a VPC.