# File lib/aws/ec2/client.rb, line 22
      def sign_request request
        version = @config.ec2_signature_version ?
          @config.ec2_signature_version.to_sym :
          (@region =~ /cn-/ ? :v4 : :v2)
        case version
        when :v4 then v4_signer.sign_request(request)
        when :v2 then v2_signer.sign_request(request)
        else
          raise "invalid signature version #{version.inspect}"
        end
      end