title: Kafka-connect, Bootstrap broker disconnected
body: <p><br/>
  Im trying to setup Kafka Connect with the intent of running a ElasticsearchSinkConnector.<br/>
  The Kafka-setup, consisting of 3 brokers secured using Kerberos, SSL and and ACL.<br/>
  <br/>
  So far Ive been experimenting with running the connect-framework and the elasticserch-server localy using docker/docker-compose (Confluent docker-image 5.4 with Kafka 2.4) connecting to the remote kafka-installation (Kafka 2.0.1 - actually our production environement).<br/></p>
  
  <pre><code>KAFKA_OPTS: -Djava.security.krb5.conf=/etc/kafka-connect/secrets/krb5.conf
        CONNECT_BOOTSTRAP_SERVERS: srv-kafka-1.XXX.com:9093,srv-kafka-2.XXX.com:9093,srv-kafka-3.XXX.com:9093
        CONNECT_REST_ADVERTISED_HOST_NAME: kafka-connect
        CONNECT_REST_PORT: 8083
        CONNECT_GROUP_ID: user-grp
        CONNECT_CONFIG_STORAGE_TOPIC: test.internal.connect.configs
        CONNECT_OFFSET_STORAGE_TOPIC: test.internal.connect.offsets
        CONNECT_STATUS_STORAGE_TOPIC: test.internal.connect.status
        CONNECT_CONFIG_STORAGE_REPLICATION_FACTOR: 1
        CONNECT_STATUS_STORAGE_REPLICATION_FACTOR: 1
        CONNECT_OFFSET_STORAGE_REPLICATION_FACTOR: 1
        CONNECT_KEY_CONVERTER: org.apache.kafka.connect.json.JsonConverter
        CONNECT_VALUE_CONVERTER: org.apache.kafka.connect.json.JsonConverter
        CONNECT_INTERNAL_KEY_CONVERTER: org.apache.kafka.connect.json.JsonConverter
        CONNECT_INTERNAL_VALUE_CONVERTER: org.apache.kafka.connect.json.JsonConverter
        CONNECT_ZOOKEEPER_CONNECT: srv-kafka-1.XXX.com:2181,srv-kafka-2.XXX.com:2181,srv-kafka-3.XXX.com:2181
        CONNECT_SECURITY_PROTOCOL: SASL_SSL
        CONNECT_SASL_KERBEROS_SERVICE_NAME: "kafka"
        CONNECT_SASL_JAAS_CONFIG: com.sun.security.auth.module.Krb5LoginModule required \
                                  useKeyTab=true \
                                  storeKey=true \
                                  keyTab="/etc/kafka-connect/secrets/kafka-connect.keytab" \
                                  principal="&lt;principal&gt;;
        CONNECT_SASL_MECHANISM: GSSAPI
        CONNECT_SSL_TRUSTSTORE_LOCATION: &lt;path_to_truststore.jks&gt;
        CONNECT_SSL_TRUSTSTORE_PASSWORD: &lt;PWD&gt;
  </code></pre>
  
  <p><br/>
  When starting the connect-framework everything seem to work fine, I can see logs claiming that the kerberos authentication is successfull etc.<br/>
  <br/>
  The problem comes when I try to start a connect-job using curl. <br/></p>
  
  <pre><code>curl -X POST -H "Content-Type: application/json" --data '{ "name": "kafka-connect", "config": { "connector.class": "io.confluent.connect.elasticsearch.ElasticsearchSinkConnector", "tasks.max": 1, "topics": "test.output.outage", "key.ignore": true, "connection.url": "http://elasticsearch1:9200", "type.name": "kafka-connect" } }' http://localhost:8083/connectors
  </code></pre>
  
  <p>The job seem to startup without issues but as soon as it is about to start consuming from the kafka-topic I get:<br/></p>
  
  <pre><code>kafka-connect     | [2020-04-06 10:35:33,482] WARN [Consumer clientId=connector-consumer-user-grp-2-0, groupId=connect-user-2] Bootstrap broker srv-kafka-1.XXX.com:9093 (id: -1 rack: null) disconnected (org.apache.kafka.clients.NetworkClient)
  </code></pre>
  
  <p>repeted in the connect-log for all brokers.<br/>
  <br/>
  What is the nature of this issue? Comunication with the brokers seem to work well - the connect-job is communicated back to the kafka as intended and when the connect-framework is restarted the job seem to resume as intended (even though still faulty).<br/>
  <br/>
  Anyone have an idea what might be causing this? or how I should go about to debug it.<br/>
  <br/>
  Since it is our production-environment I have only a limited possibility to change the server-configuration. But from what I can tell nothing in the logs seems to indicate there is something wrong. <br/>
  <br/>
  Thanks in advance</p>