Schema Registry won't start after upgrading to Confluent 4.1 - apache-kafka

Question

I have recently upgraded Confluent to 4.1 but schema registry seems to have some issues. On confluent start schema-registry (and consequently ksql-server) cannot start.
Here's the error I get in the logs of schema-registry:
[2018-04-20 11:27:38,426] ERROR Error starting the schema registry (io.confluent.kafka.schemaregistry.rest.SchemaRegistryRestApplication:65)
io.confluent.kafka.schemaregistry.exceptions.SchemaRegistryInitializationException: Error initializing kafka store while initializing schema registry
at io.confluent.kafka.schemaregistry.storage.KafkaSchemaRegistry.init(KafkaSchemaRegistry.java:203)
at io.confluent.kafka.schemaregistry.rest.SchemaRegistryRestApplication.setupResources(SchemaRegistryRestApplication.java:63)
at io.confluent.kafka.schemaregistry.rest.SchemaRegistryRestApplication.setupResources(SchemaRegistryRestApplication.java:41)
at io.confluent.rest.Application.createServer(Application.java:165)
at io.confluent.kafka.schemaregistry.rest.SchemaRegistryMain.main(SchemaRegistryMain.java:43)
Caused by: io.confluent.kafka.schemaregistry.storage.exceptions.StoreInitializationException: io.confluent.kafka.schemaregistry.storage.exceptions.StoreException: Failed to write Noop record to kafka store.
at io.confluent.kafka.schemaregistry.storage.KafkaStore.init(KafkaStore.java:139)
at io.confluent.kafka.schemaregistry.storage.KafkaSchemaRegistry.init(KafkaSchemaRegistry.java:201)
... 4 more
Caused by: io.confluent.kafka.schemaregistry.storage.exceptions.StoreException: Failed to write Noop record to kafka store.
at io.confluent.kafka.schemaregistry.storage.KafkaStore.getLatestOffset(KafkaStore.java:423)
at io.confluent.kafka.schemaregistry.storage.KafkaStore.waitUntilKafkaReaderReachesLastOffset(KafkaStore.java:276)
at io.confluent.kafka.schemaregistry.storage.KafkaStore.init(KafkaStore.java:137)
... 5 more
Caused by: java.util.concurrent.ExecutionException: org.apache.kafka.common.errors.NotLeaderForPartitionException: This server is not the leader for that topic-partition.
at org.apache.kafka.clients.producer.internals.FutureRecordMetadata.valueOrError(FutureRecordMetadata.java:94)
at org.apache.kafka.clients.producer.internals.FutureRecordMetadata.get(FutureRecordMetadata.java:77)
at org.apache.kafka.clients.producer.internals.FutureRecordMetadata.get(FutureRecordMetadata.java:29)
at io.confluent.kafka.schemaregistry.storage.KafkaStore.getLatestOffset(KafkaStore.java:418)
... 7 more
Caused by: org.apache.kafka.common.errors.NotLeaderForPartitionException: This server is not the leader for that topic-partition.
[2018-04-20 11:27:38,430] INFO Shutting down schema registry (io.confluent.kafka.schemaregistry.storage.KafkaSchemaRegistry:726)
[2018-04-20 11:27:38,430] INFO [kafka-store-reader-thread-_schemas]: Shutting down (io.confluent.kafka.schemaregistry.storage.KafkaStoreReaderThread:66)
[2018-04-20 11:27:38,431] INFO [kafka-store-reader-thread-_schemas]: Stopped (io.confluent.kafka.schemaregistry.storage.KafkaStoreReaderThread:66)
[2018-04-20 11:27:38,440] INFO [kafka-store-reader-thread-_schemas]: Shutdown completed (io.confluent.kafka.schemaregistry.storage.KafkaStoreReaderThread:66)
[2018-04-20 11:27:38,446] INFO KafkaStoreReaderThread shutdown complete. (io.confluent.kafka.schemaregistry.storage.KafkaStoreReaderThread:227)
I have no clue why this error is reported and the error messages are not that meaningful to me.
After failing, confluent start schema-registry and confluent start ksql-server bring both services up but when starting KSQL I get the following warning:
**************** WARNING ******************
Remote server address may not be valid:
Error issuing GET to KSQL server
Caused by: java.net.ConnectException: Connection refused (Connection refused)
Caused by: Could not connect to the server.
*******************************************
When trying to run a command (e.g. show tables;) the following error is reported:
ksql> show tables;
Error issuing POST to KSQL server
Caused by: java.net.ConnectException: Connection refused (Connection refused)
Caused by: Could not connect to the server.
EDIT: I've fixed this by destroying current run (confluent destroy) but it would be interesting if someone could explain this issue.

Answer 1

From the info you've posted it feels like you may have had some zombie processes or bad data somewhere, though I can't be sure.
The Schema Registry was complaining that it couldn't write a message to Kafka, because the Kafka broker was complaining that it didn't own the topic partition the Schema Registry was writing to. This might of been caused by a previous Kafka broker, (from the old install), still running.
Did you confluent stop before upgrading?
Using confluent destroy, as you did, to flatted/reset the installation is always a good option, as long as you're not precious about your data. Checking for spurious processes, (or using the old 'reboot machine' trick), can also be a good place to start when things aren't behaving as you'd expect.
Glad its all sorted now :D
Andy