gistfile1.rb

```ruby
# recipes/zones.rb
AVAILABILITY_ZONES.each do |zone|
  with_driver "aws::#{zone}" do
    aws_subnet "" do
    end
    aws_vpc "" do
    end

    machine_image "base_image_#{zone}" do
      recipe 'apt'
      recipe 'base'
    end
    machine_image "web_image_#{zone}" do
      from_image "base_image_#{zone}"
      recipe 'apache2'
      recipe 'myapp'
    end

    with_machine_options convergence_options: ... do
      include_recipe "webservers"
    end
  end
end
```

```ruby
# recipes/webservers.rb
machine 'web1' do
  from_image "web_image_#{zone}"
end
```