See also Kafka Listeners - Explained
A short post to help Googlers. On a single-node sandbox Apache Kafka / Confluent Platform installation, I was getting this error from Schema Registry, Connect, etc:
WARN [AdminClient clientId=adminclient-3] Connection to node -1 could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient) KSQL was throwing a similar error:
KSQL cannot initialize AdminCLient. I had correctly set the machine’s hostname in my Kafka server.