Getting spot instances with fog ...

add.rb

      def provision_server
        if options[:spot]
          request = compute.spot_requests.create(
            :price => price, :instance_count => 1, 
            :tags => {"Name" => generate_server_name},
            :region => region, :flavor_id => flavor, :image_id => image, 
            :security_group_ids => security_group, :key_name => keypair)
          server = nil
          Fog.wait_for { server = compute.servers.get(request.reload.instance_id) }
          server
        else
          compute.servers.create(
              :tags => {"Name" => generate_server_name},
              :region => region, :flavor_id => flavor, :image_id => image, 
              :security_group_ids => security_group, :key_name => keypair)
        end
      end