[2017-06-29T09:19:37,727][DEBUG][logstash.pipeline ] output received {"message"=>"{"my_id":"1:4656476"}"}}
This suggests that your events don't have a my_id field but that the message field contains {"my_id":"1:4656476"}, indicating that you need a json filter or a codec => json or codec => json_lines setting in your input plugin in order to deserialize the JSON payload.