ElasticsearchSinkConnector can't connect to Elastic

Question

Using the kafka-lenses-dev image, I ran into problems connecting Kafka to the local Elasticsearch 7.1.1 instance. As you can see, the connection is refused, although the instance is up and running and it's possible to curl docs in. Is the version of Elastic problematic for the connector or is the config wrong?

Config

connector.class=io.confluent.connect.elasticsearch.ElasticsearchSinkConnector
type.name=kafka-connect
key.converter.schemas.enable=false
topics=cc_data
name=elastic-sink
value.converter.schemas.enable=false
connection.url=http://localhost:9200
key.ignore=true

Error

org.apache.kafka.connect.errors.ConnectException: Couldn't start ElasticsearchSinkTask due to connection error:
    at io.confluent.connect.elasticsearch.jest.JestElasticsearchClient.<init>(JestElasticsearchClient.java:147)
    at io.confluent.connect.elasticsearch.jest.JestElasticsearchClient.<init>(JestElasticsearchClient.java:114)
    at io.confluent.connect.elasticsearch.ElasticsearchSinkTask.start(ElasticsearchSinkTask.java:120)
...
Caused by: io.searchbox.client.config.exception.CouldNotConnectException: Could not connect to http://localhost:9200
    at io.searchbox.client.http.JestHttpClient.execute(JestHttpClient.java:60)
    at io.confluent.connect.elasticsearch.jest.JestElasticsearchClient.getServerVersion(JestElasticsearchClient.java:168)
    at io.confluent.connect.elasticsearch.jest.JestElasticsearchClient.<init>(JestElasticsearchClient.java:145)
Caused by: org.apache.http.conn.HttpHostConnectException: Connect to localhost:9200 [localhost/127.0.0.1] failed: Connection refused (Connection refused)
...
Caused by: java.net.ConnectException: Connection refused (Connection refused)
...

Answer 1

You've specified Elasticsearch as being at localhost:9200. Unless Elasticsearch is running on the same container as Kafka Connect then this hostname is wrong. You need to specify the hostname of Elasticsearch in a form that is reachable from where Kafka Connect is running.

As an example, you can see an example of how to configure this based on this Docker Compose here.