Multi-Datacenter Kafka - Strata San Jose 2017
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This document discusses strategies for building large-scale stream infrastructures across multiple data centers using Apache Kafka. It outlines common multi-data center patterns like stretched clusters, active/passive clusters, and active/active clusters. It also covers challenges like maintaining ordering and consumer offsets across data centers and potential solutions.
Multi-Datacenter Kafka - Strata San Jose 2017
- 1. When One Data Center Is Not Enough Building Large-scale Stream Infrastructures Across Multiple Data Centers with Apache Kafka Gwen Shapira
- 2. There’s a book on that! Actually… a chapter
- 3. Outline Kafka overview Common multi data center patterns Future stuff
- 4. What is Kafka? ▪ It’s like a message queue, right? -Actually, it’s a “distributed commit log” -Or “streaming data platform” 0 1 2 3 4 5 6 7 8 Data Source Data Consumer A Data Consumer B
- 5. Topics and Partitions ▪ Messages are organized into topics, and each topic is split into partitions. - Each partition is an immutable, time-sequenced log of messages on disk. - Note that time ordering is guaranteed within, but not across, partitions. 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 Partition 0 Partition 1 Partition 2 Data Source Topic
- 6. Scalable consumption model Topic T1 Partition 0 Partition 1 Partition 2 Partition 3 Consumer Group 1 Consumer 1 Topic T1 Partition 0 Partition 1 Partition 2 Partition 3 Consumer Group 1 Consumer 1 Consumer 2 Consumer 3 Consumer 4
- 7. Kafka usage
- 8. Common use case Large scale real time data integration
- 9. Other use cases Scaling databases Messaging Stream processing …
- 10. Important things to remember: 1. Consumers offset commits 2. Within a cluster – each partition has replicas 3. Inter-cluster replication, producer and consumer defaults – all tuned for LAN
- 11. Why multiple data centers (DC) Offload work from main cluster Disaster recovery Geo-localization • Saving cross-DC bandwidth • Better performance by being closer to users • Some activity is just local • Security / regulations Cloud Special case: Producers with network issues
- 12. Why is this difficult? 1. It isn’t, really – you consume data from one cluster and produce to another 2. Network between two data centers can get tricky 3. Consumers have state (offsets) – syncing this between clusters get tough • And leads to some counter intuitive results
- 13. Pattern #1: stretched cluster Typically done on AWS in a single region • Deploy Zookeeper and broker across 3 availability zones Rely on intra-cluster replication to replica data across DCs Kafka producers consumer s DC 1 DC 3DC 2 producersproducers consumer s consumer s
- 14. On DC failure Producer/consumer fail over to new DCs • Existing data preserved by intra-cluster replication • Consumer resumes from last committed offsets and will see same data Kafka producers consumer s DC 1 DC 3DC 2 producers consumer s
- 15. When DC comes back Intra cluster replication auto re-replicates all missing data When re-replication completes, switch producer/consumer back Kafka producers consumer s DC 1 DC 3DC 2 producersproducers consumer s consumer s
- 16. Be careful with replica assignment Don’t want all replicas in same AZ Rack-aware support in 0.10.0 • Configure brokers in same AZ with same broker.rack Manual assignment pre 0.10.0
- 17. Stretched cluster NOT recommended across regions Asymmetric network partitioning Longer network latency => longer produce/consume time Cross region bandwidth: no read affinity in Kafka region 1 Kafk a ZK region 2 Kafk a ZK region 3 Kafk a ZK
- 18. Pattern #2: active/passive Producers in active DC Consumers in either active or passive DC Kafka producers consumer s DC 1 Replication DC 2 Kafka consumer s Critical Apps Nice Reports
- 19. Cross Datacenter Replication Consumer & Producer: read from a source cluster and write to a target cluster Per-key ordering preserved Asynchronous: target always slightly behind Offsets not preserved • Source and target may not have same # partitions • Retries for failed writes Options: • Confluent Multi-Datacenter Replication • MirrorMaker
- 20. On active DC failure Fail over producers/consumers to passive cluster Challenge: which offset to resume consumption • Offsets not identical across clusters Kafka producers consumer s DC 1 Replication DC 2 Kafka
- 21. Solutions for switching consumers Resume from smallest offset • Duplicates Resume from largest offset • May miss some messages (likely acceptable for real time consumers) Replicate offsets topic • May miss some messages, may get duplicates Set offset based on timestamp • Old API hard to use and not precise • Better and more precise API in Apache Kafka 0.10.1 (Confluent 3.1) • Nice tool coming up! Preserve offsets during replication • Harder to do
- 22. When DC comes back Need to reverse replication • Same challenge: determining the offsets Kafka producers consumer s DC 1 Replication DC 2 Kafka
- 23. Limitations Reconfiguration of replication after failover Resources in passive DC under utilized
- 24. Pattern #3: active/active Local aggregate replication to avoid cycles Producers/consumers in both DCs • Producers only write to local clusters Kafka local Kafka aggregat e Kafka aggregat e producers producer s consumer s consumer s Replication Kafka local DC 1 DC 2 consumer s consumer s
- 25. On DC failure Same challenge on moving consumers on aggregate cluster • Offsets in the 2 aggregate cluster not identical • Unless the consumers are continuously running in both clusters Kafka local Kafka aggregat e Kafka aggregat e producers producer s consumer s consumer s Replication Kafka local DC 1 DC 2 consumer s consumer s
- 27. When DC comes back No need to reconfigure replication Kafka local Kafka aggregat e Kafka aggregat e producers producer s consumer s consumer s Replication Kafka local DC 1 DC 2 consumer s consumer s
- 28. Alternative: avoid aggregate clusters Prefix topic names with DC tag Configure replication to replicate remote topics only Consumers need to subscribe to topics with both DC tags Kafka producers consumers DC 1 Replication DC 2 Kafka producers consumers
- 30. Beyond 2 DCs More DCs better resource utilization • With 2 DCs, each DC needs to provision 100% traffic • With 3 DCs, each DC only needs to provision 50% traffic Setting up replication with many DCs can be daunting • Only set up aggregate clusters in 2-3
- 31. Comparison Pros Cons Stretched • Better utilization of resources • Easy failover for consumers • Still need cross region story Active/passive • Needed for global ordering • Harder failover for consumers • Reconfiguration during failover • Resource under-utilization Active/active • Better utilization of resources • Can be used to avoid consumer failover • Can be challenging to manage • More replication bandwidth
- 32. Multi-DC beyond Kafka Kafka often used together with other data stores Need to make sure multi-DC strategy is consistent
- 33. Example application Consumer reads from Kafka and computes 1-min count Counts need to be stored in DB and available in every DC
- 34. Independent database per DC Run same consumer concurrently in both DCs • No consumer failover needed Kafka local Kafka aggregat e Kafka aggregat e producers producer s consumer consumer Replication Kafka local DC 1 DC 2 DB DB
- 35. Stretched database across DCs Only run one consumer per DC at any given point of time Kafka local Kafka aggregat e Kafka aggregat e producers producer s consumer consumer Replication Kafka local DC 1 DC 2 DB DB on failover
- 36. Practical tips • Consume remote, produce local • Unless you need encrypted data on the wire • Monitor! • Burrow for replication lag • Confluent Control Center for end-to-end • JMX metrics for rates and “busy-ness” • Tune! • Producer / Consumer tuning • Number of consumers, producers • TCP tuning for WAN • Don’t forget to replicate configuration • Separate critical topics from nice-to-have topics
- 37. Future work Offset reset tool Offset preservation “Remote Replicas” 2-DC stretch cluster Other cool Kafka future: • Exactly Once • Transactions • Headers
- 38. THANK YOU! Gwen Shapira| gwen@confluent.io | @gwenshap Kafka Training with Confluent University • Kafka Developer and Operations Courses • Visit www.confluent.io/training Want more Kafka? • Download Confluent Platform Enterprise at http://www.confluent.io/product • Apache Kafka 0.10.2 upgrade documentation at http://docs.confluent.io/3.2.0/upgrade.html • Kafka Summit recordings now available at http://kafka-summit.org/schedule/
- 39. Discount code: kafstrata Special Strata Attendee discount code = 25% off www.kafka-summit.org Kafka Summit New York: May 8 Kafka Summit San Francisco: August 28 Presented by
Editor's Notes
- #5: We earlier described Kafka as a pub-sub system, so it’s tempting to compare it to a message queue system, but the semantics are actually different from a traditional messaging service – it’s more accurate to call it a distributed commit log. Kafka was created by LinkedIn to address scalability and integration challenges they had with traditional systems. Kafka is highly scalable, fault-tolerant, high throughput, low latency, and very flexible.
- #6: Note that each partition is just a log on disk – an immutable, time-ordered sequence of messages. This goes back to why we classify this layer as “storage”. Messages are “committed” once written to all partitions.
- #18: Zookeeper used to detect failures. Communication between 1 & 3 gets disconnected. All brokers can be registered in the ZK instance in region 2. They all appear alive. Can assign leaders in all 3 regions. If we assign a leader into region 1, we then won’t be able to replicate from the leader in region 1 to region 3, which will block data from becoming accessible to consumers. Assymetric between how we detect failures and the actual network state.
- #29: Disjoint set of topics Consumers need to adjust their subscription. Can impact all applications.
- #31: With 2, need 100% of traffic supported in both to support the failure case of losing 1 DC. With 3, each DC only needs to handle extra traffic from 1. As you add more, get an N^2 pipeline, becomes daunting. Don’t need to do aggregation in all N. Generally ok to choose just 2 or 3 DCs to do aggregation. Reduces overhead.
- #33: Need to think holistically. Need to make sure all data stores use a consistent strategy.
- #35: Run independent consumers with independent databases. Easy for consumers because failures doesn’t require any coordination. But are paying full 2x costs for storage in your DB and computation.
- #36: With a stretched database, you need to run only one consumer at a time, so on failover you need to coordinate the consumers, moving from one DC to the other.