# File lib/fog/aws/requests/rds/describe_db_instances.rb, line 35
        def describe_db_instances(identifier=nil, opts={})
          response = Excon::Response.new
          server_set = []
          if identifier
            if server = self.data[:servers][identifier]
              server_set << server
            else
              raise Fog::AWS::RDS::NotFound.new("DBInstance #{identifier} not found")
            end
          else
            server_set = self.data[:servers].values
          end

          server_set.each do |server|
             case server["DBInstanceStatus"]
             when "creating"
                 if Time.now - server['InstanceCreateTime'] >= Fog::Mock.delay * 2
                   region = "us-east-1"
                   server["DBInstanceStatus"] = "available"
                   server["AvailabilityZone"] ||= region + 'a'
                   server["Endpoint"] = {"Port"=>3306, 
                                         "Address"=> Fog::AWS::Mock.rds_address(server["DBInstanceIdentifier"],region) }
                   server["PendingModifiedValues"] = {}
                 end
              when "rebooting"
                if Time.now - self.data[:reboot_time] >= Fog::Mock.delay
                  # apply pending modified values
                  server.merge!(server["PendingModifiedValues"])
                  server["PendingModifiedValues"] = {}

                  server["DBInstanceStatus"] = 'available'
                  self.data.delete(:reboot_time)
                end
              when "modifying"
                # TODO there are some fields that only applied after rebooting
                if Time.now - self.data[:modify_time] >= Fog::Mock.delay
                  server.merge!(server["PendingModifiedValues"])
                  server["PendingModifiedValues"] = {}
                  server["DBInstanceStatus"] = 'available'
                end
              when "available" # I'm not sure if amazon does this
                unless server["PendingModifiedValues"].empty?
                  server["DBInstanceStatus"] = 'modifying'
                end

             end
          end

          response.status = 200
          response.body = {
            "ResponseMetadata"=>{ "RequestId"=> Fog::AWS::Mock.request_id },
            "DescribeDBInstancesResult" => { "DBInstances" => server_set }
          }
          response
        end