Capistrano 3 (ruby) snippet to deploy to multiple AWS servers attached to ELB dynamically. Add this to production.rb (or whatever stage) instead of servers definition. AWS ec2 cli required.

elb_aws_deploy.rb

require 'rubygems'
require 'json'

LOADBALANCER = 'your-elb-load-balancer-name'

lb_instances = %x( aws elb describe-instance-health --load-balancer-name #{LOADBALANCER} )
lb_instances = JSON.parse(lb_instances)
instances = lb_instances["InstanceStates"]


ec2_cmd = "aws ec2 describe-instances --instance-ids "
instances.each do |data|
	ec2_cmd += data['InstanceId'] + " ";
end

ec2_instances = %x( #{ec2_cmd} )
ec2_instances = JSON.parse(ec2_instances)

available_ips = Array.new
parse_instances = Array.new
if ec2_instances.has_key? 'Reservations'
  reservations = ec2_instances["Reservations"]
  reservations.each do |data|
    data['Instances'].each do |instance_data|
    	server instance_data["PublicIpAddress"], user: 'ubuntu', roles: %w{web app db}, port: 22 #change to PrivateIpAddress  if using access VPN
    end
  end
end