Confluent Kafka connect ElasticSearch ID document creation - elasticsearch

Question

I'm using the kafka connect elasticsearch connector to write data from a topic to an ElasticSearch index. Both the key and value of the topic messages are in json format. The connector is not able to start because of the following error:
org.apache.kafka.connect.errors.DataException: MAP is not supported as the document id.
Following is the format of my messages (key | value):
{"key":"OKOK","start":1517241690000,"end":1517241695000} | {"measurement":"responses","count":9,"sum":1350.0,"max":150.0,"min":150.0,"avg":150.0}
And following is the body of the POST request I'm using to create the connector:
{
"name": "elasticsearch-sink-connector",
"config": {
"connector.class":"io.confluent.connect.elasticsearch.ElasticsearchSinkConnector",
"tasks.max": "1",
"topics": "output-topic-elastic",
"connection.url": "http://elasticsearch:9200",
"type.name": "aggregator",
"schemas.enable": "false",
"topic.schema.ignore": "true",
"topic.key.ignore": "false",
"value.converter": "org.apache.kafka.connect.json.JsonConverter",
"value.converter.schemas.enable": "false",
"key.converter": "org.apache.kafka.connect.json.JsonConverter",
"key.converter.schemas.enable": "false",
"key.ignore":"false",
"topic.index.map": "output-topic-elastic:aggregator",
"name": "elasticsearch-sink",
"transforms": "InsertKey",
"transforms.InsertKey.type":"org.apache.kafka.connect.transforms.ValueToKey",
"transforms.InsertKey.fields":"key"
}}
Any help would be really appreciated. I've found out a similar question on stackoverflow 1 but I've got no luck with the answers.
ES document ID creation

Answer 1

You also need ExtractField in there
"transforms": "InsertKey,extractKey",
"transforms.InsertKey.type":"org.apache.kafka.connect.transforms.ValueToKey",
"transforms.InsertKey.fields":"key",
"transforms.extractKey.type":"org.apache.kafka.connect.transforms.ExtractField$Key",
"transforms.extractKey.field":"key"
Check out this post for more details.