Kafka Simulator · 135 scenarios in 16 modules

Kafka scenarios: 135 interactive simulations

Every scenario is a recorded run of the simulator's Apache Kafka 4.3 engine. Each page walks through it step by step and opens the playground at any step. To build your own cluster instead, start in free play.

Kafka errors and symptoms, with the scenario that reproduces each

Kafka configs explained, each with the scenario that shows it

Anatomy 8 scenarios

Kafka topics, partitions and offsets explained · Beginner · 2 min
Kafka write path: one record from producer to consumer · Beginner · 1 min
Kafka message keys: how a key picks the partition · Beginner · 2 min
Kafka offsets are per partition, not global · Beginner · 2 min
Kafka replication factor, leader and follower replicas · Beginner · 2 min
Kafka high watermark vs log end offset (LEO) · Intermediate · 2 min
Why Kafka consumers cannot read past the high watermark · Intermediate · 2 min
Kafka log start offset: why the earliest offset is not 0 · Intermediate · 2 min

Producers & EOS 12 scenarios

Kafka producer acks=0: fire and forget, silent data loss · Intermediate · 2 min
Kafka producer acks=1: acknowledged by the leader only · Intermediate · 2 min
Kafka acks=0 vs acks=1 vs acks=all on a degraded ISR · Intermediate · 2 min
Kafka acks=1 data loss: min.insync.replicas does not help · Intermediate · 3 min
Kafka linger.ms vs batch.size: when the producer sends · Intermediate · 3 min
Kafka producer partitioners: keyed, round-robin and sticky · Intermediate · 3 min
Kafka compression.type: fewer, larger producer batches · Intermediate · 3 min
Kafka buffer.memory and max.block.ms: producer backpressure · Intermediate · 3 min
Kafka idempotent producer: retrying NOT_ENOUGH_REPLICAS · Intermediate · 2 min
Kafka enable.idempotence=false: a retry writes a duplicate · Intermediate · 2 min
Kafka idempotent producer dedup vs a plain producer · Intermediate · 3 min
Kafka max.in.flight.requests.per.connection and ordering · Intermediate · 3 min

Consumer groups 13 scenarios

Kafka consumer poll loop: subscribe, poll, fetch · Intermediate · 2 min
Kafka auto.offset.reset: earliest vs latest vs none · Intermediate · 3 min
Kafka committed offsets: enable.auto.commit and restart · Intermediate · 3 min
Replay a Kafka topic: consumed records stay in the log · Intermediate · 3 min
Kafka consumer group: how partitions split across members · Intermediate · 2 min
Kafka consumer group rebalance when a consumer joins · Intermediate · 3 min
Kafka partition assignors: range vs round-robin vs sticky · Advanced · 3 min
Kafka eager vs cooperative rebalancing (cooperative-sticky) · Advanced · 4 min
Kafka consumer crash and session.timeout.ms · Intermediate · 3 min
Kafka max.poll.interval.ms: evicting a stuck consumer · Intermediate · 3 min
Kafka static membership: group.instance.id avoids rebalances · Intermediate · 4 min
Kafka consumer lag: why it grows and how it drains · Intermediate · 3 min
Evicted Kafka consumer: how a survivor takes its partition · Intermediate · 3 min

Replication 12 scenarios

Kafka ISR (in-sync replicas): how replicas leave and rejoin · Intermediate · 2 min
min.insync.replicas with acks=all: when Kafka refuses writes · Beginner · 1 min
Kafka slow follower: replica.lag.time.max.ms and the ISR · Intermediate · 2 min
Kafka high watermark pinned by a slow in-sync replica · Intermediate · 3 min
Losing two Kafka brokers with min.insync.replicas=2 · Intermediate · 2 min
Kafka preferred leader election after a rack failure · Advanced · 3 min
Kafka unclean.leader.election.enable: offline or data loss · Advanced · 3 min
Kafka unclean leader election: permanent loss of acked data · Advanced · 4 min
Kafka log truncation when an old leader returns · Advanced · 4 min
Kafka broker.rack: rack-aware replica placement · Advanced · 3 min
Kafka rack-aware reassignment after adding a rack · Advanced · 3 min
Increase the replication factor of an existing Kafka topic · Intermediate · 2 min

Transactions 10 scenarios

Kafka at-most-once vs at-least-once vs exactly-once · Intermediate · 3 min
At-least-once delivery in Kafka: where duplicates come from · Intermediate · 3 min
Kafka transaction commit vs abort with read_committed · Advanced · 3 min
Kafka isolation.level: read_committed vs read_uncommitted · Advanced · 3 min
Kafka last stable offset (LSO) with concurrent transactions · Advanced · 3 min
Kafka transaction.timeout.ms: the coordinator aborts · Advanced · 3 min
Kafka read_committed during a leader election · Advanced · 3 min
Kafka consume-process-produce loop with exactly-once · Advanced · 3 min
Kafka zombie producer fencing with transactional.id · Advanced · 3 min
Kafka processing.guarantee=exactly_once_v2 end to end · Advanced · 4 min

Storage 12 scenarios

Kafka retention.ms and a consumer that falls behind · Intermediate · 3 min
Kafka retention.bytes: size-based log retention · Intermediate · 2 min
Kafka OFFSET_OUT_OF_RANGE with auto.offset.reset=none · Intermediate · 2 min
Kafka log compaction: cleanup.policy=compact explained · Intermediate · 2 min
Kafka tombstones: deleting a key with delete.retention.ms · Intermediate · 3 min
Kafka cleanup.policy=compact,delete: both policies at once · Intermediate · 3 min
Kafka tiered storage: offloading old segments to remote · Advanced · 2 min
Kafka tiered storage: a consumer reads from the remote tier · Advanced · 3 min
Kafka local.retention.ms vs retention.ms in tiered storage · Advanced · 4 min
Diskless Kafka topics (KIP-1163): the write path · Advanced · 3 min
Diskless vs classic Kafka: cross-AZ replication traffic · Advanced · 3 min
Diskless Kafka produce latency: the price of object storage · Advanced · 3 min

KRaft 4 scenarios

What the Kafka controller does when a broker dies · Intermediate · 3 min
Kafka KRaft quorum: losing a majority of controllers · Intermediate · 4 min
Kafka KRaft controller failover and metadata log catch-up · Advanced · 4 min
Kafka ZooKeeper vs KRaft: what freezes leader elections · Advanced · 4 min

Operations 6 scenarios

Add a Kafka broker and reassign partitions onto it · Intermediate · 3 min
Remove a Kafka broker safely: drain it first · Intermediate · 3 min
kafka-reassign-partitions: change a replica set by hand · Intermediate · 2 min
Kafka replication throttle during partition reassignment · Intermediate · 3 min
Change Kafka min.insync.replicas at runtime, no restart · Intermediate · 2 min
producer_byte_rate: how a Kafka client quota throttles · Intermediate · 3 min

Chaos 6 scenarios

Kafka broker failure: how the partition leader fails over · Intermediate · 3 min
Kafka split-brain: what a network partition does to leaders · Intermediate · 3 min
Kafka network partition: the majority side keeps writing · Intermediate · 3 min
Kafka NOT_ENOUGH_REPLICAS: brokers failing one by one · Intermediate · 4 min
Kafka ISR re-expansion: how a restarted broker catches up · Intermediate · 3 min
Kafka rack failure: why RF=4 on two racks refuses writes · Intermediate · 3 min

Disaster recovery 22 scenarios

Kafka stretched cluster across two data centers · Advanced · 3 min
2.5-DC Kafka stretched cluster with a witness site · Advanced · 3 min
3-DC Kafka cluster: the KRaft quorum survives losing a site · Advanced · 3 min
Kafka in two DCs without a witness: KRaft quorum is lost · Advanced · 3 min
Kafka data center failure: leader failover to the other DC · Advanced · 3 min
Kafka network split inside one DC: ISR drops to the floor · Advanced · 3 min
Kafka MirrorMaker 2 active-passive DR and replication lag · Advanced · 3 min
Kafka DR failover with MirrorMaker 2: measuring RPO · Advanced · 4 min
Active-active Kafka with MirrorMaker 2 and region topics · Advanced · 3 min
MirrorMaker 2 offset translation for Kafka consumer failover · Advanced · 4 min
Kafka failback after a MirrorMaker 2 DR failover · Advanced · 4 min
Active-active Kafka DR drill: move clients to the survivor · Advanced · 5 min
Confluent MRC observers: Kafka replicas outside the ISR · Advanced · 3 min
Kafka observer lag in Confluent Multi-Region Clusters · Advanced · 3 min
Kafka observer promotion in Confluent Multi-Region Clusters · Advanced · 4 min
Confluent MRC observer promotion: losing the Kafka leader DC · Advanced · 5 min
Kafka replica placement: durability vs latency across DCs · Advanced · 4 min
Confluent Cluster Linking: offset-preserving Kafka mirroring · Advanced · 4 min
Kafka mirror topics (Confluent): read-only until promoted · Advanced · 4 min
Cluster Linking vs MirrorMaker 2 for Kafka replication · Advanced · 4 min
Kafka consumer offset sync: Cluster Linking vs MirrorMaker 2 · Advanced · 4 min
Kafka failover and failback with Confluent Cluster Linking · Advanced · 5 min

Tiered storage 2 scenarios

Kafka tiered storage lifecycle: offload, read back, expire · Advanced · 4 min
Kafka tiered storage with infinite retention (Redpanda) · Advanced · 4 min

Schema registry 3 scenarios

Confluent Schema Registry subjects and versions for Kafka · Intermediate · 3 min
Kafka schema compatibility: BACKWARD vs FORWARD vs FULL · Advanced · 4 min
Kafka breaking schema change rejected by Schema Registry · Advanced · 3 min

Authorization (ACLs & RBAC) 2 scenarios

TopicAuthorizationException: authorizing a Kafka producer · Intermediate · 3 min
Confluent RBAC role bindings for Kafka topics · Intermediate · 3 min

Capstones 5 scenarios

Kafka exactly-once pipeline that survives a region failover · Advanced · 5 min
Zero data loss through a Kafka DC outage with Confluent MRC · Advanced · 4 min
Zero-downtime Kafka migration with Confluent Cluster Linking · Advanced · 4 min
Multi-region active-active Kafka event backbone · Advanced · 4 min
Tune Kafka throughput: linger.ms, batch.size and zstd · Advanced · 4 min

Terminal ops 9 scenarios

Kafka from the terminal: hosts, ssh and the KRaft controller · Intermediate · 3 min
Diagnose consumer lag with kafka-consumer-groups --describe · Intermediate · 3 min
Kafka log segments on disk: leader vs follower · Intermediate · 3 min
Under-replicated vs under-min-ISR partitions in Kafka · Intermediate · 3 min
Reset Kafka consumer group offsets with --to-earliest · Intermediate · 3 min
Set retention.ms on a live topic with kafka-configs · Intermediate · 3 min
Kafka partition reassignment: execute, throttle, verify · Intermediate · 4 min
Graceful broker shutdown with kafka-server-stop · Intermediate · 3 min
Kafka tools on two clusters: --bootstrap-server decides · Advanced · 4 min

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