Exactly-Once, Again: Adding EOS Support for Kafka Connect Source Connectors with Chris Egerton

1. Exactly-Once, Again: Adding EOS Support for Kafka Connect Source Connectors Chris Egerton

2. Nice to meet you! Chris Egerton Open Source Program Office @Aiven Apache Kafka committer and PMC member (Official bio) (Unofficial bio)

3. Exactly-Once, Again: Adding EOS Support for Kafka Connect Source Connectors

4. ● “Exactly-once semantics” ● “Semantics” instead of “delivery”, “guarantees”, “delivery guarantees”, etc. (see Two Generals’ Problem) ● Levels: ○ Probably-once ○ At-least-once ○ At-most-once ○ Exactly-once ● With all else equal, exactly-once is best ● But of course, it’s the hardest to implement EOS

6. Source Connectors ● Kafka stores and transmits events. Where do these events come from, and where do they go? ● DYI producer/consumer application? Nah 👎 ● Connectors: no-code (or low-code) applications to integrate Kafka with other systems ● Sink connectors write data from Kafka to the external system ● Source connectors read data from the external system into Kafka

8. Kafka Connect ● Distributed, horizontally-scalable, fault- tolerant ingest/export tool for Kafka ● Developers implement connectors against the Kafka Connect API ● Cluster administrators install connectors onto one or more Kafka Connect workers, which combine to form a cluster ● Users can then create and manage connectors on that cluster by submitting JSON configurations via a REST API ● (For users) No code required! { "name": "local-file-source", "connector.class": "FileStreamSink", "tasks.max": "1", "file": "test.txt", "topic": "connect-test" }

9. We’re going to talk about designing support for exactly-once semantics (EOS) with source connectors developed for Kafka Connect. In summary…

10. Challenges 1⃣ƿ Ø#μГ& Г& όƿ „)} +Ρ#ƿ )μμ„#–„ 2⃣ƿ q–)+Г& όƿ / & 0ƿ +#–+Г#¤Г& όƿ „)} +Ρ#ƿ )μμ„#–„ 3⃣ƿ ò#–+№ Г& όƿ 0#Ю Г¤#+№ ƿ –)ƿ ǽ/ μЧ/ 4⃣ƿ̀ )8 ΛГ#„ƿ 🧟🧟🧟🧟🧟

11. Source offsets, in detail ● Source connectors provide source records ● Source records come with source offsets (partition + offset) ● On startup, connectors use source offsets to know where to resume from ● Source offsets are stored in an offsets topic by Kafka Connect ✅🎉 // TODO ɀ Ø"μГ%Г%όƿ „)} +Ρ#ƿ )μμ„#–„ƿ ;1⃣<ƿ Г„ƿ –φ#ƿ +#„ъ)& „ГΛГЮ Г–№ ƿ )μƿ –φ#ƿ Ρ)& & #Ρ–)+ ɀ q–)*Г%όƿ , %-ƿ *"–*Г"¤Г%όƿ „)} +Ρ#ƿ )μμ„#–„ƿ ;2⃣<ƿ Г„ƿ –φ#ƿ +#„ъ)& „ГΛГЮ Г–№ ƿ )μƿ ǽ/μЧ/ƿ Ņ)& & #Ρ–

12. Exactly-once for Kafka clients ɀ ǽ@ nBCDEƿ ŚG/ Ρ–Ю № ƿ H& Ρ#ƿ Ø#Ю Г¤#+№ ƿ / & 0ƿ ſ +/ & „/ Ρ–Г)& / Ю ƿ ë #„„/ όГ& ό ɂ ò#Ю #/ „#0ƿ Г& ƿ LMNNMLML ɂ O #& Ρ#P ƿ Q ό/ Г& Sƿ Г& ƿ –φ#ƿ –Г–Ю # ɀ / -"0 ъ)–"%–ƿ ъ*)-} Ρ"*Tƿ +#–+Г#„ƿ $ Г–φ)} –ƿ 0} ъЮ ГΡ/ –#„ƿ ;3⃣< ɀ ſ *, %„, Ρ–Г)%, Ю ƿ ъ*)-} Ρ"*Tƿ / –)8 ГΡƿ Ρ+)„„V –)ъГΡƿ $ +Г–#„ ɀ ſ *, %„, Ρ–Г)%, Ю ƿ / Ø„Tƿ „Г& όЮ #ƿ $ +Г–#+ƿ ъ#+ƿ @ Ø ɂ / %Г–Г, Ю Г7"ƿ –*, %„, Ρ–Г)%„ƿ $ Г–φƿ / ƿ ъ+)0} Ρ#+ƿ –)ƿ μ"%Ρ"ƿ )} –ƿ )–φ#+ƿ ъ+)0} Ρ#+„ƿ $ Г–φƿ –φ#ƿ „/ 8 #ƿ –+/ & „/ Ρ–Г)& / Ю ƿ @ Ø ✅🎉

13. Tracking source offsets (2⃣) Ļ #μ)+#T ɀ n)Ю Ю ƿ Ρ)& & #Ρ–)+ƿ μ)+ƿ „)} +Ρ#ƿ +#Ρ)+0„ ɀ ỳ +Г–#ƿ +#Ρ)+0„ƿ –)ƿ ǽ/ μЧ/ ɀ n#+Г)0ГΡ/ Ю Ю № ƿ $ +Г–#ƿ ;Ρ)8 8 Г–<ƿ „)} +Ρ#ƿ )μμ„#–„ƿ –)ƿ ǽ/ μЧ/ ɀ n+)¤Г0#„ƿ / –V Ю #/ „–V )& Ρ#ƿ „} ъъ)+– μ–#+T ɀ Ļ #όГ& ƿ –+/ & „/ Ρ–Г)& ɀ n)Ю Ю ƿ Ρ)& & #Ρ–)+ƿ μ)+ƿ „)} +Ρ#ƿ +#Ρ)+0„ ɀ ỳ +Г–#ƿ +#Ρ)+0„ƿ Г8 8 #0Г/ –#Ю № ƿ –)ƿ ǽ/ μЧ/ ƿ ;„–ГЮ Ю < ɀ ỳ +Г–#ƿ „)} +Ρ#ƿ )μμ„#–„ƿ –)ƿ ǽ/ μЧ/ ƿ ɀ Ņ)8 8 Г–ƿ –+/ & „/ Ρ–Г)& ɀ n+)¤Г0#„ƿ #G/ Ρ–Ю № V )& Ρ#ƿ „} ъъ)+– ✅🎉

14. 75% done! 1⃣ƿ Ø#μГ& Г& όƿ „)} +Ρ#ƿ )μμ„#–„ 2⃣ƿ q–)+Г& όƿ / & 0ƿ +#–+Г#¤Г& όƿ „)} +Ρ#ƿ )μμ„#–„ 3⃣ƿ ò#–+№ Г& όƿ 0#Ю Г¤#+№ ƿ –)ƿ ǽ/ μЧ/ 🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟 🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟 🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟🧟 ✅ ✅ ✅ 4⃣ƿ ſ φ/ –ƿ Ю #/¤#„Y

15. “Chekhov’s gun cabinet” Kafka Connect: diving deeper ɀ Ņ)%%"Ρ–)*„ƿ ό#& #+/–#ƿ Ρ)& μГό} +/–Г)& „ƿ μ)+ƿ )& #ƿ )+ƿ 8 )+#ƿ –, „Ч„ ɀ ſ / „Ч„ƿ Ρ/ & ƿ Λ#ƿ „ъ+#/ 0ƿ / Ρ+)„„ƿ 8 } Ю –ГъЮ #ƿ ǽ/ μЧ/ ƿ Ņ)& & #Ρ–ƿ $ )+Ч#+„ ɀ ſ / „Ч„ƿ / +#ƿ / „„Гό& #0ƿ –)ƿ $ )+Ч#+„ƿ 0} +Г& όƿ / ƿ *"Λ, Ю , %Ρ" ɀ ƿ „Г& όЮ #ƿ $ )+Ч#+P ƿ –φ#ƿ Ю ", -"*P ƿ 0#–#+8 Г& #„ƿ –φ/ –ƿ / „„Гό& 8 #& – ɀ ſ / „Чƿ Ρ)& μГό} +/ –Г)& „ƿ / +#ƿ „–)+#0ƿ Г& ƿ / ƿ „Г& όЮ #V ъ/+–Г–Г)& ƿ ǽ/μЧ/ƿ –)ъГΡƿ Ρ/ Ю Ю #0ƿ –φ#ƿ Ρ)%μГόƿ –)ъГΡ ɀ Z)+ƿ „)} +Ρ#ƿ Ρ)& & #Ρ–)+„P ƿ ǽ/ μЧ/ ƿ Ņ)& & #Ρ–ƿ } „#„ƿ )& #ƿ ъ+)0} Ρ#+ƿ ъ#+ƿ –/ „Чƿ –)ƿ „#& 0ƿ „)} +Ρ#ƿ +#Ρ)+0„ƿ –)ƿ ǽ/μЧ/

16. Zombie fencing: correctness goals ſ )Ю #+/ –#0ƿ „Ρ#& / +Г)„T ɀ ;[ & <ό+/ Ρ#μ} Ю ƿ $ )+Ч#+ƿ „φ} –0)$ & ɀ +ΛГ–+/ +№ ƿ $ )+Ч#+ƿ „–/ +–} ъ„ ɀ +ΛГ–+/ +ГЮ № V Ю )& όP ƿ / +ΛГ–+/ +ГЮ № V ъЮ /Ρ#0P ƿ / & 0ƿ /+ΛГ–+/+ГЮ № V –Г8 #0ƿ ъ/ } „#„

17. Zombie fencing: UX goals ● Minimal unnecessary interruptions (keep processing data) ● Minimal changes to connector code ● Minimal connector management API changes

18. Zombie fencing: actually pretty easy? ● Give each task a transactional ID derived from the name of the connector and the task ID ○ E.g., “reddit-source-0” or “chris-ksl-3” ● Let tasks fence out older instances on startup ○ Fencing: disabling a producer from writing to Kafka

19. Zombie fencing: actually pretty easy? reddit-source-0 reddit-source-1 reddit-source-2 reddit-source-3 ò#00Г–ƿ „)} +Ρ#ƿ ;)Ю 0ƿ –/ „Ч„< reddit-source-0 reddit-source-1 reddit-source-2 reddit-source-3 ò#00Г–ƿ „)} +Ρ#ƿ ;& #$ ƿ –/ „Ч„< Fences out ;"%Ρ"„ƿ )} – ;"%Ρ"„ƿ )} – Fences out ɀ q)Y ƿ 0)#„ƿ –φГ„ƿ $ )+Ч ɀ ])Ю ƿ @ ƿ $ Г„φƿ 🥲

20. Source partition reshuffling problem ɀ q)} +Ρ#ƿ Ρ)& & #Ρ–)+„ƿ +#/ 0ƿ μ+)8 ƿ „)} *Ρ"ƿ ъ, *–Г–Г)%„ ɂ Ø/ –/ Λ/ „#ƿ –/ ΛЮ #„P ƿ ǽ/ μЧ/ ƿ –)ъГΡ„P ƿ #–ΡM ɀ ſ φ#„#ƿ / +#ƿ / Ю Ю )Ρ/ –#0ƿ / Ρ+)„„ƿ –/ „Ч„ ɀ ſ φ/ –ƿ / Ю Ю )Ρ/ –Г)& ƿ Ρ/ & ƿ Ρφ/ & ό#ƿ )¤#+ƿ –Г8 #

21. Source partition reshuffling problem P0 Task 0 P1 ſ / „Чƿ N @ & Г–Г/ Ю ƿ / Ю Ю )Ρ/ –Г)& ƿ ^Ţƿ –/ „Ч„P ƿ Ţƿ ъ/ +–Г–Г)& „< P0 Task 0 P2 ƿ & #$ ƿ ъ/ +–Г–Г)& ƿ ^nŢ`ƿ Г„ƿ Ρ+#/ –#0 P1 ſ / „Чƿ N & ƿ #GГ„–Г& όƿ ъ/ +–Г–Г)& ƿ ^nN`ƿ Г„ƿ 0#Ю #–#0 P0 ſ / „Чƿ L P2 ſ / „Чƿ N P1 P2

22. Source partition reshuffling problem P0 ſ / „Чƿ L P2 HЮ 0ƿ –/ „Ч„ P1 Task 1 ﬀ #$ ƿ –/ „Ч„ P2 ſ / „Чƿ N ;"%Ρ"„ƿ )} – ● New task T1 starts before old task T0 stops ɀ Ļ )–φƿ / +#ƿ / „„Гό& #0ƿ ъ/+–Г–Г)& ƿ nŢ ɀ Ø} ъЮ ГΡ/ –#„ƿ / Λ)} & 0b

23. Zombie fencing: second try ɀ ỳ φ#& #¤#+ƿ & #$ ƿ –/„Чƿ Ρ)& μГό} +/–Г)& „ƿ /+#ƿ +#/0ƿ μ+)8 ƿ –φ#ƿ Ρ)& μГόƿ –)ъГΡP ƿ ъ#+μ)+8 ƿ /ƿ +)} & 0ƿ )μƿ 7)0 ΛГ"ƿ μ"%ΡГ%ό ɂ Z)+ƿ #¤#+№ ƿ & #$ ƿ –/ „ЧP ƿ –/ Ч#ƿ Г–„ƿ –+/ & „/ Ρ–Г)& / Ю ƿ @ Øƿ / & 0ƿ ъ+##8 ъ–Г¤#Ю № ƿ Г& Г–Г/Ю Гc#ƿ –+/& „/Ρ–Г)& „ ɀ ﬀ )$ ƿ Г–d„ƿ Г8 ъ)„„ГΛЮ #ƿ μ)+ƿ / &№ ƿ )Ю 0#+ƿ Г& „–/ & Ρ#„ƿ )μƿ & #$ Ю № V Ρ+#/ –#0ƿ –/ „Ч„ƿ –)ƿ Λ#ƿ +} & & Г& όƿ Λ#μ)+#ƿ / &№ ƿ & #$ #+ƿ Г& „–/ & Ρ#„ƿ / +#ƿ „–/ +–#0 ɀ Ø)ƿ –φГ„ƿ 0} +Г& όƿ +#Λ/ Ю / & Ρ#

24. Zombie fencing: first try reddit-source-0 reddit-source-1 reddit-source-2 reddit-source-3 ò#00Г–ƿ „)} +Ρ#ƿ ;)Ю 0ƿ –/ „Ч„< reddit-source-0 reddit-source-1 reddit-source-2 reddit-source-3 ò#00Г–ƿ „)} +Ρ#ƿ ;& #$ ƿ –/ „Ч„< ;"%Ρ"„ƿ )} – Fences out ;"%Ρ"„ƿ )} – ;"%Ρ"„ƿ )} –

25. Zombie fencing: second try reddit-source-0 reddit-source-1 reddit-source-2 reddit-source-3 ò#00Г–ƿ „)} +Ρ#ƿ ;)Ю 0ƿ –/ „Ч„< reddit-source-0 reddit-source-1 reddit-source-2 reddit-source-3 ò#00Г–ƿ „)} +Ρ#ƿ ;& #$ ƿ –/ „Ч„< ` )0 ΛГ"ƿ μ"%ΡГ%ό *)} %- ● Woohoo, we did it! ● Just kidding, put your hand back down

26. Zombie fencing: second try ɀ ỳ φ#& #¤#+ƿ & #$ ƿ –/„Чƿ Ρ)& μГό} +/–Г)& „ƿ /+#ƿ +#/0ƿ μ+)8 ƿ –φ#ƿ Ρ)& μГόƿ –)ъГΡP ƿ ъ#+μ)+8 ƿ /ƿ +)} & 0ƿ )μƿ 7)0 ΛГ"ƿ μ"%ΡГ%ό ɂ Z)+ƿ #¤#+№ ƿ & #$ ƿ –/ „ЧP ƿ –/ Ч#ƿ Г–„ƿ –+/ & „/ Ρ–Г)& / Ю ƿ @ Øƿ / & 0ƿ ъ+##8 ъ–Г¤#Ю № ƿ Г& Г–Г/Ю Гc#ƿ –+/& „/Ρ–Г)& „ ɀ ﬀ )$ ƿ Г–d„ƿ Г8 ъ)„„ГΛЮ #ƿ μ)+ƿ / &№ ƿ )Ю 0#+ƿ Г& „–/ & Ρ#„ƿ )μƿ & #$ Ю № V Ρ+#/ –#0ƿ –/ „Ч„ƿ –)ƿ Λ#ƿ +} & & Г& όƿ Λ#μ)+#ƿ / &№ ƿ & #$ #+ƿ Г& „–/ & Ρ#„ƿ / +#ƿ „–/ +–#0 ɀ Ø)ƿ –φГ„ƿ 0} +Г& όƿ +#Λ/ Ю / & Ρ#

27. Connector resizing T0 T1 T2 T3 Z)} +ƿ –/ „Ч„ T0 T1 T2 ſ φ+##ƿ –/ „Ч„ ` )0 ΛГ"ƿ μ"%ΡГ%ό *)} %-= * - based on new tasks ɀ HЮ 0ƿ –/ „Чƿ +} & & Г& όƿ / μ–#+ƿ & #$ #+ƿ –/ „Ч„ƿ / +#ƿ „–/ +–#0 ɀ @ μƿ / ƿ ъ/ +–Г–Г)& ƿ Г„ƿ +#/„„Гό& #0ƿ μ+)8 ƿ )Ю 0ƿ ſ e ƿ –)ƿ & #$ ƿ ſ Lfſ Nfſ ŢY ɀ Ø} ъЮ ГΡ/ –#„ƿ / Λ)} & 0

28. Zombie fencing: third time’s the charm ɀ @ & „–#/ 0ƿ )μƿ } „Г& όƿ –φ#ƿ & #$ ƿ „#–ƿ )μƿ –/ „Чƿ Ρ)& μГό„ƿ μ)+ƿ )} +ƿ +)} & 0ƿ )μƿ c)8 ΛГ#ƿ μ#& ΡГ& όP ƿ } „#ƿ –φ#ƿ )Ю 0ƿ „#– ɀ ό/ Г& P ƿ 0)ƿ –φГ„ƿ 0} +Г& όƿ +#Λ/ Ю / & Ρ# ɀ Ю +Гόφ–P ƿ –φГ„ƿ φ/ „ƿ –)ƿ Λ#ƿ #& )} όφP ƿ +Гόφ– ɀ ỳ #Ю Ю Y ƿ φ)$ ƿ 0)ƿ $ #ƿ Ч& )$ ƿ / Λ)} –ƿ –φ#ƿ )Ю 0ƿ „#–ƿ )μƿ –/ „Чƿ Ρ)& μГό„

29. Zombie leaders ɀ ſ φ#ƿ Ю #/ 0#+ƿ )μƿ –φ#ƿ ΡЮ } „–#+ƿ Г„ƿ –φ#ƿ )& Ю № ƿ )& #ƿ / Ю Ю )$ #0ƿ –)ƿ ъ} ΛЮ Г„φƿ –/ „Чƿ Ρ)& μГό„ƿ –)ƿ –φ#ƿ Ρ)& μГόƿ –)ъГΡ ɀ O )$ #¤#+P ƿ $ #ƿ 0)& d–ƿ #& μ)+Ρ#ƿ –φГ„ƿ ¤#+№ ƿ „–+)& όЮ № ɀ q)8 #ƿ $ )+Ч#+„ƿ 8 /№ ƿ 8 Г„–/ Ч#& Ю № ƿ Λ#Ю Г#¤#ƿ –φ#№ ƿ / +#ƿ –φ#ƿ Ю #/ 0#+ ɀ @ & / ΡΡ} +/ –#ƿ –/ „Чƿ Ρ)& μГό„ƿ 8 /№ ƿ Λ#ƿ ъ} ΛЮ Г„φ#0ƿ Г& ƿ +/ ъГ0ƿ „} ΡΡ#„„Г)& P ƿ )¤#+$ +Г–Г& όƿ ¤/ Ю Г0ƿ –/ „Чƿ Ρ)& μГό„

30. ● Leader should fence out three tasks ● But leader only fences out two Zombie leaders my-connector (3 tasks) Ņ)%μГόƿ –)ъГΡ my-connector (2 tasks) my-connector (1 task) q–/ +–Г& όƿ „–/ –# Write by zombie leader ỳ +Г–#ƿ Λ№ ƿ / Ρ–} / Ю ƿ Ю #/ 0#+ ò#Λ/ Ю / & Ρ# Ś¤"%– ɀ H& ƿ +#Λ/ Ю / & Ρ#P ƿ Ю #/ 0#+ƿ „##„T ○ One new task ɂ ſ $ )ƿ )Ю 0ƿ –/ „Ч„

31. Zombie fencing: guarded config topic ɀ O )$ ƿ 0)ƿ $ #ƿ ъ+#¤#& –ƿ c)8 ΛГ#ƿ Ю #/ 0#+„ƿ μ+)8 ƿ / ΡΡ#„„Г& όƿ –φ#ƿ Ρ)& μГόƿ –)ъГΡ ɀ ſ +/ & „/ Ρ–Г)& / Ю ƿ ъ+)0} Ρ#+ƿ –)ƿ –φ#ƿ +#„Ρ} #ƿ ;/ ό/ Г& <b ɀ @ „ƿ –φГ„ƿ #& )} όφ ɀ +#ƿ $ #ƿ ό} / +/ & –##0ƿ –φ/ –ƿ –φ#ƿ Ρ)& μГόƿ –)ъГΡƿ Ρ/ & ƿ Λ#ƿ } „#0ƿ / „ƿ / ƿ „)} +Ρ#ƿ )μƿ –+} –φƿ μ)+ƿ c)8 ΛГ#ƿ μ#& ΡГ& όƿ & )$ ɀ 🙃🙃🙃

32. Leadership change ɀ @ μƿ / ƿ Ю #/ 0#+ƿ μ/ Ю Ю „ƿ )} –ƿ )μƿ –φ#ƿ ΡЮ } „–#+P ƿ / ƿ & #$ ƿ )& #ƿ Г„ƿ Ρφ)„#& ɀ O )$ ƿ 0)#„ƿ –φ#ƿ & #$ ƿ Ю #/ 0#+ƿ Ч& )$ ƿ $ φ/ –ƿ & ##0„ƿ μ#& ΡГ& ό

33. Leadership change (with new tasks) my-connector (3 tasks) Config topic my-connector (2 tasks) q–/ +–Г& όƿ „–/ –# ỳ +Г–#ƿ Λ№ ƿ Ю #/ 0#+ ò#Λ/ Ю / & Ρ#ƿ ;g ƿ c)8 ΛГ#ƿ μ#& ΡГ& ό< Leader falls out of cluster Ś¤"%– ɀ H& ƿ μГ+„–ƿ +#Λ/ Ю / & Ρ#P ƿ )Ю 0ƿ –/ „Ч„ƿ / +#ƿ μ#& Ρ#0ƿ )} –ƿ „} ΡΡ#„„μ} Ю Ю № Rebalance (+ new leader) ɀ H& ƿ „#Ρ)& 0ƿ +#Λ/ Ю / & Ρ#P ƿ & #$ ƿ Ю #/ 0#+ƿ 0)#„& d–ƿ φ/¤#ƿ –)ƿ 0)ƿ / &№ ƿ μ#& ΡГ& ό

34. Leadership change (with new tasks) my-connector (3 tasks) Config topic my-connector (2 tasks) q–/ +–Г& όƿ „–/ –# Write by leader ]#/ 0#+ƿ μ/ Ю Ю „ƿ )} –ƿ )μƿ ΡЮ } „–#+ƿ ;Λ#μ)+#ƿ +#Λ/ Ю / & Ρ#< ò#Λ/ Ю / & Ρ#ƿ ;g ƿ & #$ ƿ Ю #/ 0#+< Ś¤"%– ɀ H& ƿ +#Λ/ Ю / & Ρ#P ƿ & #$ ƿ Ю #/ 0#+ƿ φ/ „ƿ –)ƿ μ#& Ρ#ƿ )} –ƿ )Ю 0ƿ –/ „Ч„ ● But how can it tell? ɀ ſ φ#ƿ Ρ)& μГόƿ –)ъГΡƿ Ю ))Ч„ƿ –φ#ƿ „/ 8 #ƿ Г& ƿ Λ)–φƿ „Ρ#& / +Г)„ ɀ ò#8 #8 Λ#+P ƿ $ #ƿ $ / & –ƿ –)ƿ /¤)Г0ƿ } & & #Ρ#„„/ +№ ƿ Г& –#++} ъ–Г)& „

35. Zombie fencing: fence, then write ɀ Ņ} ++#& –ƿ „#я } #& Ρ#ƿ )μƿ #¤#& –„T ɂ n} ΛЮ Г„φƿ & #$ ƿ –/ „Чƿ Ρ)& μГό„ ɂ ò#Λ/ Ю / & Ρ# ɂ i ƿ̀ )8 ΛГ#ƿ μ#& ΡГ& ό ɂ q–/ +–ƿ & #$ ƿ –/ „Ч„ ɀ ﬀ #$ ƿ )+0#+T ɂ ` )8 ΛГ#ƿ μ#& ΡГ& ό ɂ n} ΛЮ Г„φƿ & #$ ƿ –/ „Чƿ Ρ)& μГό„ ɂ ò#Λ/ Ю / & Ρ# ɂ q–/ +–ƿ & #$ ƿ –/ „Ч„ ɀ ſ φГ„ƿ φ/ „ƿ –)ƿ Λ#ƿ Г–P ƿ +Гόφ– ɀ j )} ƿ $ Г„φƿ 😈

36. That was not a good idea ● Poor UX ○ Causes tasks to fail in between zombie fencing and end of rebalance ○ Forcibly kills them, no chance to commit pending offsets ○ Looks like a bug to users ● Correctness issue ○ Users can manually restart failed tasks ○ Even in between zombie fencing and publishing new task configs ○ Uh oh, a zombie task made it to the other end of the rebalance!

37. Zombie fencing: durable task counts ● Forget the “fence then write” logic ● Instead, we explicitly track the number of to-be-fenced tasks in the config topic with a task count record ● These serve two purposes: ○ Explicitly: if fencing is necessary, how many tasks have to be fenced out ○ Implicitly: determine whether zombie fencing is necessary

38. Zombie fencing: durable task counts my-connector (3 tasks) Ņ)%μГόƿ –)ъГΡ my-connector (2 tasks) my-connector-task-count (2) q–/ +–Г& όƿ „–/ –# ﬀ #$ ƿ –/ „Чƿ Ρ)& μГό„ Rebalance (+ zombie fencing) Ś¤"%– ɀ H& ƿ +#Λ/ Ю / & Ρ#T ɂ ]#/ 0#+ƿ μ#& Ρ#„ƿ –φ+##ƿ –/ „Ч„ƿ Λ/ „#0ƿ )& ƿ Ю / –#„–ƿ –/ „Чƿ Ρ)} & –ƿ +#Ρ)+0 ɂ ]#/ 0#+ƿ $ +Г–#„ƿ & #$ ƿ –/ „Чƿ Ρ)} & –ƿ )μƿ –$ )ƿ –/ „Ч„ƿ Λ/ „#0ƿ )& ƿ Ю / –#„–ƿ –/ „Чƿ Ρ)& μГό„ my-connector-task-count (3)

39. Zombie fencing: durable task counts my-connector (3 tasks) Config topic my-connector (2 tasks) my-connector-task-count (2) q–/ +–Г& όƿ „–/ –# ﬀ #$ ƿ –/ „Чƿ Ρ)& μГό„ Rebalance (+ zombie fencing) Ś¤"%– my-connector-task-count (3) Safe to run bring up tasks? ✅ ❌ ✅

40. ɀ ỳ φ/–ƿ Ρ)} Ю 0ƿ ъ)„„ГΛЮ № ƿ Λ+#/Чƿ –φГ„ƿ & )$ ɀ Hφƿ № #/ φP ƿ $ φ/ –ƿ $ / „ƿ –φ/ –ƿ / Λ)} –ƿ –/ „Чƿ +#„–/ +–„ Zombie fencing: durable task counts

41. Laggy task startup ● Zombie fencing disables all initialized task producers from writing to Kafka ● What if a zombie task lags and hasn’t initialized its producer by the time zombie fencing for a new generation of tasks takes place? ● Or, what if a task is restarted on a zombie worker after zombie fencing takes place?

42. Laggy task startup reddit-source-0 reddit-source-1 reddit-source-2 reddit-source-3 ò#00Г–ƿ „)} +Ρ#ƿ ^k ƿ )Ю 0ƿ –/ „Ч„< reddit-source-0 reddit-source-1 reddit-source-2 ò#00Г–ƿ „)} +Ρ#ƿ ^e ƿ & #$ ƿ –/ „Ч„< ` )0 ΛГ"ƿ μ"%ΡГ%ό *)} %- reddit-source-3 ^ſ / „Чƿ Г„ƿ Ю / όόГ& όƿ 0} +Г& όƿ „–/ +–} ъ< ^ſ / „Чƿ φ/ „ƿ μГ& Г„φ#0ƿ „–/ +–} ъ<

43. Zombie fencing: check your work ɀ μ–#+ƿ Г& Г–Г/ Ю ГcГ& όƿ –+/ & „/ Ρ–Г)& „ƿ μ)+ƿ / ƿ –/ „Чƿ ъ+)0} Ρ#+P ƿ φ/¤#ƿ –)ƿ 8 / Ч#ƿ „} +#ƿ Г–d„ƿ „–ГЮ Ю ƿ „/ μ#ƿ –)ƿ +} & ƿ –φ#ƿ –/ „Ч ɀ ﬀ #$ ƿ „#я } #& Ρ#ƿ )μƿ #¤#& –„T ɂ Ø#ΡГ0#ƿ –)ƿ ;+#<„–/ +–ƿ –/ „Ч ɂ Ņ+#/ –#ƿ ъ+)0} Ρ#+ƿ μ)+ƿ –/ „Чƿ / & 0ƿ Г& Г–Г/ Ю Гc#ƿ –+/ & „/ Ρ–Г)& „ ɂ ò#/ 0ƿ –)ƿ #& 0ƿ )μƿ Ρ)& μГόƿ –)ъГΡ ɂ @ μƿ & #$ ƿ –/ „Чƿ Ρ)& μГό„ƿ μ)} & 0P ƿ / Λ)+–ƿ „–/ +–} ъƿ / & 0ƿ / Λ/ & 0)& ƿ –φ#ƿ –/ „Ч ɂ H–φ#+$ Г„#P ƿ „/ μ#ƿ –)ƿ „–/ +–ƿ ъ+)Ρ#„„Г& όƿ 0/ –/ ɀ O /¤#ƿ $ #ƿ μГ& / Ю Ю № ƿ 0)& #ƿ Г–

44. 🎉🎉🎉 Yes! 🎉🎉🎉 (But…)

45. Caveats ● Fencing during rebalancing is not a good idea ○ Makes rebalances more brittle ○ Requires a new rebalance any time we want to restart a task that failed due to failed zombie fencing ● Instead, we fence outside of rebalances ○ During task startup, workers issue a REST request to the leader to perform zombie fencing for the connector ○ The leader will perform that round (if necessary), then send back a 2XX response ○ If a non-2XX response is received, the task is marked failed ○ Tasks can easily be restarted

46. Caveats ɀ ſ φ+)$ / $ /№ ƿ ъ+)0} Ρ#+„ƿ μ)+ƿ Г& Г–Г/ Ю ГcГ& όƿ –+/ & „/ Ρ–Г)& „ƿ Г„ƿ $ / „–#μ} Ю ɀ ỳ #ƿ / 00#0ƿ / ƿ & #$ ƿ / 08 Г& ƿ ΡЮ Г#& –ƿ n@ ƿ Г& ƿ e Me ƿ –)ƿ 0)ƿ –φГ„ƿ Г& „–#/ 0 ɀ ỳ #ƿ φ/¤#ƿ –)ƿ Λ#ƿ Ρ/ +#μ} Ю ƿ / Λ)} –ƿ φ)$ ƿ –φ#ƿ Ю #/ 0#+ƿ } „#„ƿ –φ#ƿ –+/ & „/ Ρ–Г)& / Ю ƿ ъ+)0} Ρ#+ ɀ qГ8 ГЮ / +ƿ QΡЮ / Г8 V –φ#& V Ρφ#ΡЧSƿ Ю )όГΡƿ –)ƿ „)} +Ρ#ƿ –/ „Ч„

47. In practice @ 8 ъЮ #8 #& –/ –Г)& ƿ 0#–/ ГЮ „ƿ / +#ƿ Λ)+Г& όP ƿ φ)$ ƿ 0)ƿ $ #ƿ / Ρ–} / Ю Ю № ƿ } „#ƿ –φГ„ƿ μ#/ –} +#

48. In practice (cluster administrators) ɀ ﬀ #$ ƿ ΡЮ } „–#+„T ɂ [ „#ƿ ¤#+„Г)& ƿ e Me MLƿ )+ƿ Ю / –#+ ɂ Ņ)& μГό} +#ƿ #¤#+№ ƿ $ )+Ч#+ƿ $ Г–φƿ exactly.once.source.support = enabled ɀ ŚGГ„–Г& όƿ ΡЮ } „–#+„T ɂ ò)Ю Ю Г& όƿ } ъό+/ 0#ƿ NE ɂ Ļ +Г& όƿ / Ю Ю ƿ $ )+Ч#+„ƿ –)ƿ e Me MLƿ )+ƿ Ю / –#+ ɂ Ņ)& μГό} +#ƿ #¤#+№ ƿ $ )+Ч#+ƿ $ Г–φƿ exactly.once.source.support = preparing ○ ò)Ю Ю Г& όƿ } ъό+/ 0#ƿ ŢE ɂ Ņ)& μГό} +#ƿ #¤#+№ ƿ $ )+Ч#+ƿ $ Г–φƿ exactly.once.source.support = enabled

49. In practice (downstream readers) ● Have to filter out records from aborted transactions ● If using the Java consumer, configure with isolation.level = read_committed ● For sink connectors, do at least one of the following: ○ Configure worker with consumer.isolation.level = read_committed ○ Configure connector with consumer.override.isolation.level = read_committed with (3.0.0 or later, with default worker configuration)

50. In practice (writing connectors) Have to define source offsets correctly public abstract class SourceTask { public abstract List<SourceRecord> poll(); } public class SourceRecord { public SourceRecord(Map<String, ?> sourcePartition, Map<String, ?> sourceOffset, ...) }

51. In practice (writing connectors) O /¤#ƿ –)ƿ } „"ƿ „)} +Ρ#ƿ )μμ„#–„ƿ Ρ)++#Ρ–Ю № public abstract class SourceTask { protected SourceTaskContext context; public abstract void start(Map<String, String> props); } public interface SourceTaskContext { OffsetStorageReader offsetStorageReader(); } public interface OffsetStorageReader { <T> Map<Map<String, T>, Map<String, Object>> offsets(Collection<Map<String, T>> partitions); }

52. In summary ɀ ŚG/ Ρ–Ю № V )& Ρ#ƿ Г„ƿ φ/ +0ƿ –)ƿ Г8 ъЮ #8 #& – ɂ Ś„ъ#ΡГ/ Ю Ю № ƿ φ/ & 0Ю Г& όƿ c)8 ΛГ#ƿ $ )+Ч#+„fc)8 ΛГ#ƿ –/ „Ч„ƿ / Ρ+)„„ƿ –/ „Чƿ +#Ρ)& μГό} +/ –Г)& „ ɀ ŚG/ Ρ–Ю № V )& Ρ#ƿ Г„ƿ ;φ)ъ#μ} Ю Ю № <ƿ #/ „№ ƿ –)ƿ } „# ɂ @ μƿ Г–d„ƿ & )–P ƿ φ/ +/ „„ƿ ъГ& όƿ 8 #ƿ )& ƿ ăГ+/b ɂ φ––ъ„TffГ„„} #„M/ ъ/ Ρφ#M)+όfТ Г+/ fъ+)Т #Ρ–„fǽ Zǽ fГ„„} #„ ɀ Z)+ƿ / Ю Ю ƿ –φ#ƿ 0#–/ ГЮ „P ƿ Ρφ#ΡЧƿ )} –ƿ ǽ@ nBnND ɂ φ––ъ„TffΡ$ ГЧГM/ ъ/ Ρφ#M)+όfΡ)& μЮ } #& Ρ#f0Г„ъЮ /№ fǽ Zǽ fǽ@ n BnNDṊ e i ŚG/ Ρ–Ю № V H& Ρ#g q} ъъ)+–g μ)+g q)} +Ρ#g Ņ)& & #Ρ–)+„

53. Thank you! ƿ Open Source Program Office @Aiven Ρφ#Г„&' ( Г¤&* +Г, Chris Egerton -Г* -Ρφ#Г„. &ό&#–,* . 12 33456 3 @C0urante

Exactly-Once, Again: Adding EOS Support for Kafka Connect Source Connectors with Chris Egerton

Exactly-Once, Again: Adding EOS Support for Kafka Connect Source Connectors with Chris Egerton

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