Kafka InconsistentGroupProtocolException: Cause and Fix
Kafka InconsistentGroupProtocolException: the group member's supported protocols are incompatible. Why it hits mid-upgrade and how to fix the assignor mismatch.
Java
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Kafka FencedInstanceIdException: Fix Static Membership Collisions
FencedInstanceIdException means two live consumers share one group.instance.id. Here's why the broker fences the old one, and how to fix it for good.
Kafka "Failed to construct kafka consumer": Every Cause, Fixed
KafkaException: Failed to construct kafka consumer — how to triage every common cause (deserializer class, classpath, DNS, JAAS, SSL) and fix each one fast.
Kafka Failed to Acquire Lock on File .lock: How to Fix It
Kafka broker won't start: 'Failed to acquire lock on file .lock ... A Kafka instance in another process is using this directory.' Why it happens and how to fix it.
Kafka CorruptRecordException: Record Is Corrupt — Fix It
Kafka CorruptRecordException: Record is corrupt (stored crc != computed crc). Why the CRC check fails, how to recover the partition, and how to stop it recurring.
Kafka: Consumer Is Not Subscribed to Any Topics — Fix
IllegalStateException: Consumer is not subscribed to any topics or assigned any partitions — why poll() throws it, the subscribe/assign contract, and the fix.
Fix KafkaConsumer Is Not Safe for Multi-Threaded Access
Hitting ConcurrentModificationException: KafkaConsumer is not safe for multi-threaded access? Here's why the thread guard fires and the correct fix.
Kafka Connect Failed to Flush: Offset Commit Timeout Fix
Kafka Connect source task logs 'Failed to flush, timed out while waiting for producer to flush outstanding N messages'. Here's the real cause and the fix.
Kafka Connect: Failed to Find Any Class That Implements Connector
Kafka Connect throws 'Failed to find any class that implements Connector' when plugin.path is wrong or classloader isolation hides your JAR. Here's the fix.
Kafka SerializationException: Can't Convert Value of Class Fix
Kafka SerializationException: Can't convert value of class X to StringSerializer? The ClassCastException behind it, the config fix, and the safer design.