kafka-avro-console-producer - Error registering Avro schema / io.confluent.kafka.schemaregistry.client.rest.exceptions.RestClientException

By default, the kafka-avro-console-producer will assume that the schema registry is on port 8081, and happily connect to it. Unfortunately, this can lead to some weird errors if another process happens to be listening on port 8081 already!

[oracle@bigdatalite tmp]$ kafka-avro-console-producer \
>  --broker-list localhost:9092 --topic kudu_test \
>  --property value.schema='{"type":"record","name":"myrecord","fields":[{"name":"id","type":"int"},{"name":"random_field", "type": "string"}]}'

{"id": 999, "random_field": "foo"}

org.apache.kafka.common.errors.SerializationException: Error registering Avro schema: {"type":"record","name":"myrecord","fields":[{"name":"id","type":"int"},{"name":"random_field","type":"string"}]}
Caused by: io.confluent.kafka.schemaregistry.client.rest.exceptions.RestClientException: Unexpected character ('<' (code 60)): expected a valid value (number, String, array, object, 'true', 'false' or 'null')
 at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@4e0ae11f; line: 1, column: 2]; error code: 50005
        at io.confluent.kafka.schemaregistry.client.rest.RestService.sendHttpRequest(RestService.java:170)
        at io.confluent.kafka.schemaregistry.client.rest.RestService.httpRequest(RestService.java:187)
        at io.confluent.kafka.schemaregistry.client.rest.RestService.registerSchema(RestService.java:238)
        at io.confluent.kafka.schemaregistry.client.rest.RestService.registerSchema(RestService.java:230)
        at io.confluent.kafka.schemaregistry.client.rest.RestService.registerSchema(RestService.java:225)
        at io.confluent.kafka.schemaregistry.client.CachedSchemaRegistryClient.registerAndGetId(CachedSchemaRegistryClient.java:59)
        at io.confluent.kafka.schemaregistry.client.CachedSchemaRegistryClient.register(CachedSchemaRegistryClient.java:91)
        at io.confluent.kafka.serializers.AbstractKafkaAvroSerializer.serializeImpl(AbstractKafkaAvroSerializer.java:72)
        at io.confluent.kafka.formatter.AvroMessageReader.readMessage(AvroMessageReader.java:158)
        at kafka.tools.ConsoleProducer$.main(ConsoleProducer.scala:55)
        at kafka.tools.ConsoleProducer.main(ConsoleProducer.scala)

Solution? Make sure you specify the schema URL when you launch the producer, using --property schema.registry.url=http://localhost:18081 :

kafka-avro-console-producer \
--broker-list localhost:9092 --topic kudu_test \
--property value.schema='{"type":"record","name":"myrecord","fields":[{"name":"id","type":"int"},{"name":"random_field", "type": "string"}]}' \
--property schema.registry.url=http://localhost:18081