Kafka Streams: Perfectly Balanced as all things should be
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John Roesler, Confluent, Software Engineer Kafka Streams cluster management is getting a huge overhaul. We are tackling many of the hardest problems in distributed systems to solve the biggest pain points in managing Streams application clusters. There are numerous improvements recently completed or in progress right now: * Fast ownership transfer of tasks (KIP-429) * Balanced assignment of tasks (KIP-441) * Background state migration (KIP-441) * High-availability Interactive Query (KIP-535) * Graceful recovery from exceptions (KIP-572) This talk is a deep dive into our solution to distributing and managing stateful workloads in Kafka Streams application clusters. We'll talk about the assignment algorithm itself, as well as how Streams is able to keep the cluster up for processing and serving queries while state gets migrated around the cluster in the background. We'll go over the configurations and log messages as well as the behavior you'll observe when operating your cluster. Finally, we will talk about future opportunities for Streams cluster management and open the floor for discussion. https://www.meetup.com/Dallas-Kafka/events/270468566/
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Kafka Streams: Perfectly Balanced as all things should be
- 1. Perfectly Balanced, as All Streams Should Be John Roesler vvcephei@apache.org https://s.apache.org/perfectly-balanced-streams
- 2. Problem 1: Cluster workload becomes skewed after adding nodes Problem 2: Long restoration/rebalance pauses after adding nodes
- 3. builder .stream("sentences") .flatMapValues(whitespaceSplitter) .groupBy((k, v) -> v) .count() .toStream() .to("word-counts"); sentences split repartition count word-counts
- 4. “the quick brown fox” “it was the best of times” “it was the worst of times” best brown fox it it of of quick the the the times times was was worst 1 best 1 brown 1 fox 2 it 2 of 1 quick 3 the 2 times 2 was 1 worst sentences split repartition count word-counts
- 7. sentences-0 split repartition-1 count word-counts sentences-1 split repartition-0 count repartition-2 count Task 0_0 Task 1_0 Task 0_1 Task 1_1 Task 1_2
- 8. sentences-0 split repartition-1 count word-counts sentences-1 split repartition-0 count repartition-2 count Task 0_0 Task 1_0 Task 0_1 Task 1_1 Task 1_2
- 9. Task 0_0 Task 1_0 Task 0_1 Task 1_1 Task 1_2
- 10. Task 0_0 Task 1_0 Task 0_1 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Active Stateless Active Stateful Standby (Stateful)
- 11. Pop Quiz: Is it balanced?
- 12. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2
- 13. Balance Checklist ● Balance the overall number of tasks
- 14. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2
- 15. Balance Checklist ● Balance the overall number of tasks ● Balance the active tasks
- 16. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Host 1 Host 2 Task 0_2
- 17. Balance Checklist ● Balance the overall number of tasks ● Balance the active tasks ● Balance stateful tasks
- 18. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2
- 19. Assignment Checklist ● Balance the overall number of tasks ● Balance the active tasks ● Balance stateful tasks ● For each task, assign standby to different hosts than active
- 20. Task 1_0 Task 1_1 Task 1_2 Host 1 Host 2 Task 0_0 Task 0_1 Task 0_1
- 21. Assignment Checklist ● Balance the overall number of tasks ● Balance the active tasks ● Balance stateful tasks ● For each task, assign standby to different hosts than active ● Balance partitions for each task across nodes
- 22. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2
- 23. Problem 1: Cluster workload becomes skewed after adding nodes Problem 2: Long restoration/rebalance pauses after adding nodes
- 24. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2 Problem 1: Cluster workload becomes skewed after adding nodes Host 3
- 25. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2 Problem 1: Cluster workload becomes skewed after adding nodes Host 3
- 26. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2 Problem 2: Long restoration/rebalance pauses after adding nodes Host 3
- 27. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0Task 1_1 Host 1 Host 2 Problem 2: Long restoration/rebalance pauses after adding nodes Host 3
- 28. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2 Solution: Warm up the new host before moving stateful tasks Host 3
- 29. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2 Solution: Warm up the new host before moving stateful tasks Host 3 Task 1_2 Task 1_0
- 31. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_0 Task 1_1 Host 1 Host 2 Solution: Warm up the new host before moving stateful tasks Host 3 Task 1_2 Task 1_0
- 32. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_1 Host 1 Host 2 Solution: Warm up the new host before moving stateful tasks Host 3 Task 1_0
- 33. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_1 Host 1 Host 2 What if we lose a node? Host 3 Task 1_0
- 34. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_1 Host 1 Host 2 What if we lose a node? Host 3 Task 1_0
- 35. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Host 1 Host 2 What if we lose a node? Host 3 Task 1_0
- 36. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_1 Host 1 Host 2 What if we lose a node? Host 3 Task 1_0
- 37. Later on, Host 2 comes back
- 38. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_1 Host 1 Host 2 What if we lose a node? (Recovery) Host 3 Task 1_0
- 39. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_1 Host 1 Host 2 What if we lose a node? (Recovery) Host 3 Task 1_0 Task 1_2 Task 1_1
- 41. Task 0_0 Task 0_1 Task 1_0 Task 1_1 Task 1_2 Task 1_2 Task 1_1 Host 1 Host 2 What if we lose a node? (Recovery) Host 3 Task 1_0 Task 1_2 Task 1_1
- 42. Task 0_0 Task 0_1 Task 1_0 Task 1_2 Task 1_1 Task 1_1 Host 1 Host 2 What if we lose a node? (Recovery) Host 3 Task 1_0 Task 1_2
- 43. Configs to care about num_standbys acceptable_recovery_lag probing_rebalance_interval_ms max_warmup_replicas
- 44. Other tips Register a StateRestoreListener to monitor progress: KafkaStreams#setGlobalStateRestoreListener onRestoreStart( TopicPartition topicPartition, String storeName, long startingOffset, long endingOffset ); onBatchRestored( TopicPartition topicPartition, String storeName, long batchEndOffset, long numRestored ); onRestoreEnd(TopicPartition topicPartition, String storeName, long totalRestored);
- 45. Best log messages to watch out for INFO Decided on assignment: {...} with followup probing rebalance INFO Scheduled a followup probing rebalance for ... ms. INFO Finished unstable assignment of tasks, a followup probing rebalance will be triggered. INFO Decided on assignment: {...} with no followup probing rebalance INFO Finished stable assignment of tasks, no followup rebalances required.
- 46. Kafka-Summit.org A T T E N D S P E A K COMMUNITY DISCOUNT 25% OFF Use the discount code KSA20Meetup at kafka-summit.org/ Submit a proposal to speak in Austin Deadline 17 May 2020 Apply at kafka-summit.org/