Queues, Kafka and event-driven interview questions
Queues vs pub/sub, Kafka partitions and consumer groups, delivery semantics, ordering, dead letters, backpressure, event sourcing and schema evolution.
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Questions
- Work queues vs publish/subscribePick the fix
- Background job queuesOrder the steps
- Kafka partitions, keys and orderingPick the fix
- Consumer groups and rebalancingPredict
- Committing offsets: at-most-once vs at-least-onceSpot the bug
- Keeping messages in orderPredict
- Dead-letter queues and poison messagesPick the fix
- Idempotent consumers and deduplicationPredict
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Quick facts
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Kafka ordering
Guaranteed only within a partition, never across a whole topic.
Kafka 4
Runs in KRaft mode only; ZooKeeper support was removed in 4.0.
Idempotent producer
Enabled by default since Kafka 3.0; stops producer retries from writing duplicates.
Consumers vs partitions
A group can't have more active consumers than partitions; extras sit idle (seen in our Kafka 4.1.2 run).
Partitioner difference
The Java client hashes keys with murmur2;
librdkafkadefaults to a CRC32-based partitioner.Redis pub/sub
Fire-and-forget: subscribers that aren't connected miss messages. Streams keep them.
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Sources: Topic outline informed by System Design Primer by Donne Martin and the Zalando RESTful API Guidelines, both licensed under CC BY 4.0. Every question and answer is written by Best Latest Apps. Credits and license