Kafka Sink Connector fails: Schema not found; error code: 40403

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I have a sink connector with the following configuration

{
    "name": "sink-test-mariadb-MY_TOPIC",
    "config": { 
                "connector.class":"io.confluent.connect.jdbc.JdbcSinkConnector",
                "tasks.max":"10",
                "topics":"MY_TOPIC",
                "connection.url":"jdbc:mariadb://localhost:3306/myschema?user=myuser&password=mypass",
                "auto.create":"false",
                "auto.evolve":"true",
                "table.name.format":"MY_TABLE",
                "pk.mode":"record_value",
                "pk.fields":"ID",
                "insert.mode":"upsert",
                "transforms":"ExtractField",
                "transforms.ExtractField.type":"org.apache.kafka.connect.transforms.ExtractField$Value",
                "transforms.ExtractField.field":"data"
        }
}

and after a while all the tasks of the connector fail with the following error: 

{
    "state": "FAILED",
    "trace": "org.apache.kafka.connect.errors.DataException: MY_TOPIC
                at io.confluent.connect.avro.AvroConverter.toConnectData(AvroConverter.java:95)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.convertMessages(WorkerSinkTask.java:468)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:301)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:205)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:173)
                at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:170)
                at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:214)
                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)
            Caused by: org.apache.kafka.common.errors.SerializationException: Error retrieving Avro schema for id 802
            Caused by: io.confluent.kafka.schemaregistry.client.rest.exceptions.RestClientException: Schema not found; error code: 40403
                at io.confluent.kafka.schemaregistry.client.rest.RestService.sendHttpRequest(RestService.java:202)
                at io.confluent.kafka.schemaregistry.client.rest.RestService.httpRequest(RestService.java:229)
                at io.confluent.kafka.schemaregistry.client.rest.RestService.getId(RestService.java:409)
                at io.confluent.kafka.schemaregistry.client.rest.RestService.getId(RestService.java:402)
                at io.confluent.kafka.schemaregistry.client.CachedSchemaRegistryClient.getSchemaByIdFromRegistry(CachedSchemaRegistryClient.java:119)
                at io.confluent.kafka.schemaregistry.client.CachedSchemaRegistryClient.getBySubjectAndId(CachedSchemaRegistryClient.java:192)
                at io.confluent.kafka.schemaregistry.client.CachedSchemaRegistryClient.getById(CachedSchemaRegistryClient.java:168)
                at io.confluent.kafka.serializers.AbstractKafkaAvroDeserializer.deserialize(AbstractKafkaAvroDeserializer.java:121)
                at io.confluent.kafka.serializers.AbstractKafkaAvroDeserializer.deserializeWithSchemaAndVersion(AbstractKafkaAvroDeserializer.java:194)
                at io.confluent.connect.avro.AvroConverter$Deserializer.deserialize(AvroConverter.java:120)
                at io.confluent.connect.avro.AvroConverter.toConnectData(AvroConverter.java:83)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.convertMessages(WorkerSinkTask.java:468)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:301)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:205)
                at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:173)
                at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:170)
                at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:214)
                at java.util.concurrent.Executors$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)",
    "id": 0,
    "worker_id": "localhost:8083"
}

The connector manages to synchronise the topic with tha database but it suddenly fails without any reason. I am also very sure that the schema is there. Its subject appears in the list returned by calling schema registry API localhost:8081/subjects 

[
  ...
  MY_TOPIC-value
  ...
]
confluent-schema-registry apache-kafka avro
2 Answers

The message on the Kafka topic is serialised with a different version of the schema that the one you have on the Schema Registry. Perhaps it was generated by a tool that wrote the schema to a different Schema Registry, or in a different environment? In order to be able to deserialise it Kafka Connect needs to be able to retrieve the schema ID that is in the magic byte at the beginning of the Kafka message on the topic.

The schema is not present on your Schema Registry, as seen by : 

GET /schemas/ids/803
 { "error_code": 40403, "message": "Schema not found" }

You can inspect the ID of the schema that you do have by looking at

curl -s "http://localhost:8081/subjects/MY_TOPIC-value/versions/3/"|jq '.id'
user_3506130

I had the same problem and I realized that the code 40403 doesn't really mean that the schema was not found, it means that the schema does not correspond to the required one. a different code exists in case the schema was not found at all (40401).

So all I did was to change the schema accordingly and it worked for me.

user_116284110
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