creates capistrano autoscaling_servers command to get instance list from AWS autoscaling groups

autoscaling.rb

require 'aws-sdk-v1'
require 'capistrano/framework'

@autoscaling_groups = []

def autoscaling_servers(opts = {})
  Array(opts[:regions]).each do |region|
    AWS::AutoScaling.new(region: region).groups[opts[:group]].tap do |group|
      @autoscaling_groups.push(group)
    end.ec2_instances.each do |instance|
      if instance.status == :running
        server instance.ip_address, roles: opts[:roles], user: opts[:user]
      end
    end
  end
end

def load_balancers(opts = {})
  Array(opts[:regions]).map do |region|
    AWS::AutoScaling.new(region: region).groups[opts[:group]].load_balancer_names
  end
end

namespace :aws do

  desc 'ssh and run command on servers, e.g. cap staging "aws:servers[hostname]"'
  task :ssh, :cmd do |task, args|
    on roles(:all) do |server|
      execute args[:cmd]
    end
  end

  desc 'List server IPs'
  task :servers do
    on roles(:all) do |server|
      puts "#{server}\n"
    end
  end

  desc 'List load-balancers and instance health'
  task :elb do
    @autoscaling_groups.map(&:load_balancers).flatten.each do |lb|
      puts "#{lb.name}:"
      lb.instances.health.each do |h|
        puts "#{h[:instance].public_ip_address}\t#{h.state}"
      end
    end
  end

end

## helpful aliases
task :elb => 'aws:elb'
task :lb  => 'aws:elb'

production.rb

## example usage
require 'autoscaling'

set :stage, :production
set :application, 'web-prod@*'
set :branch, 'master'

autoscaling_servers group: 'web-prod',  regions: %w[us-east-1], user: 'core', roles: %w[app web]