Record-based processors should be writing the "record.count" attribute to outgoing flow files, but PutElasticsearchHttpRecord does not currently. I have written NIFI-5356 to cover this improvement. In the meantime, if you are using other record-based processors upstream, you may find you already have a record.count attribute, and since PutElasticsearchHttpRecord transfers the entire flow file to either success or failure, then if the attribute is there and the flow file is transferred to success, then "record.count" correctly indicates the number of records loaded into ES by that processor (for that flow file).