Skip to content

Gopi Gorantala

I'm Gopi — 15+ years in Java, building Kafka and Flink platforms for banks, where one lost event is a financial discrepancy. I write javahandbook.com because the guides I needed didn't exist. Everything here is tested against a real cluster first.

Kafka RebalanceInProgressException: Why It Happens and How to Fix It

Kafka RebalanceInProgressException on commitSync/commitAsync with CooperativeStickyAssignor? Here's why it's not CommitFailedException, and the correct 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 "Connection to node -1 could not be established" — Fix

Fix Kafka's "Connection to node -1 (localhost/127.0.0.1:9092) could not be established. Broker may not be available" — the Docker advertised.listeners fix.

Kafka IllegalStateException: No Current Assignment for Partition

Getting java.lang.IllegalStateException: No current assignment for partition on seek()? Why Kafka's lazy assignment causes it — and the correct fix.

Kafka Connect Task Threw an Uncaught and Unrecoverable Exception

Kafka Connect task killed with 'uncaught and unrecoverable exception'? It's usually a converter poison pill. Here's the DataException root cause, DLQ fix, and design.

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.

5 Steps to Ace Your FAANG Interview: Checklists for DSA, LLD & HLD

Stop grinding blindly. Follow this structured 5-phase checklist to master Data Structures, Low-Level Design, System Architecture, and behavioral questions for major tech company interviews.

Kafka: Cannot Perform Operation After Producer Closed

Kafka IllegalStateException 'Cannot perform operation after producer has been closed' explained: why it happens, the Spring share