Hickups with Kafka Elasticsearch WorkerSinkTask initialization

[FlorianNachtigall]

elasticsink connector fails and restarts regularly due to error in WorkerSinkTask initialization:

[2020-06-29 10:31:11,342] INFO Finished starting connectors and tasks (org.apache.kafka.connect.runtime.distributed.DistributedHerder)
ERROR StatusLogger No log4j2 configuration file found. Using default configuration: logging only errors to the console. Set system property 'log4j2.debug' to show Log4j2 internal initialization logging.
[2020-06-29 10:31:13,838] ERROR WorkerSinkTask{id=elasticsink-0} Task threw an uncaught and unrecoverable exception (org.apache.kafka.connect.runtime.WorkerTask)
java.lang.IllegalArgumentException: Address must be resolved but wasn't - InetSocketAddress#getAddress() returned null
	at org.elasticsearch.common.transport.TransportAddress.<init>(TransportAddress.java:64)
	at com.sksamuel.elastic4s.xpack.security.XPackElasticClient$$anonfun$apply$2.apply(XPackElasticClient.scala:25)
	at com.sksamuel.elastic4s.xpack.security.XPackElasticClient$$anonfun$apply$2.apply(XPackElasticClient.scala:24)
	at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:733)
	at scala.collection.immutable.List.foreach(List.scala:392)
	at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:732)
	at com.sksamuel.elastic4s.xpack.security.XPackElasticClient$.apply(XPackElasticClient.scala:24)
	at com.datamountaineer.streamreactor.connect.elastic6.KElasticClient$.getClient(KElasticClient.scala:69)
	at com.datamountaineer.streamreactor.connect.elastic6.ElasticWriter$.apply(ElasticWriter.scala:44)
	at com.datamountaineer.streamreactor.connect.elastic6.ElasticSinkTask.start(ElasticSinkTask.scala:56)
	at org.apache.kafka.connect.runtime.WorkerSinkTask.initializeAndStart(WorkerSinkTask.java:302)
	at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:191)
	at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:175)
	at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:219)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
[2020-06-29 10:31:13,843] ERROR WorkerSinkTask{id=elasticsink-0} Task is being killed and will not recover until manually restarted (org.apache.kafka.connect.runtime.WorkerTask)
[2020-06-29 10:31:13,843] INFO Stopping Elastic sink. (com.datamountaineer.streamreactor.connect.elastic6.ElasticSinkTask)