Kafka Summit SF 2017 - Kafka and the Polyglot Programmer
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An Overview of the Kafka clients ecosystem. APIs – wire protocol clients – higher level clients (Streams) – REST Languages (with simple snippets – full examples in GitHub) – the most developed clients – Java and C/C++ – the librdkafka wrappers node-rdkafka, python, GO, C# – why use wrappers Shell scripted Kafka ( e.g. custom health checks) kafkacat Platform gotchas (e.g. SASL on Win32) Presented at Kafka Summit SF 2017 by Edoardo Comar and Andrew Schofield, IBM
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Kafka Summit SF 2017 - Kafka and the Polyglot Programmer
- 1. © 2017 IBM Corporation Edoardo Comar ecomar@uk.ibm.com Andrew Schofield andrew_schofield@uk.ibm.com IBM Message Hub Kafka and the Polyglot Programmer A brief overview of the Kafka clients ecosystem
- 2. © 2017 IBM Corporation Session objectives • Show some comparable Kafka usage from different languages • Show a little of what goes underneath a Kafka client • To appreciate the heavy lifting a client has to do • We’ll proceed in reverse order though J
- 3. © 2017 IBM Corporation How does an application talk to Kafka ? • Protocol-level client libraries (implementing the Kafka “wire” API) • The “official” Java client • librdkafka C/C++ library and wrappers for other languages • Other clients from a large open-source ecosystem • Alternative “message-level” APIs • Kafkacat, REST • Higher-level APIs • Kafka Connect, Kafka Streams
- 4. © 2017 IBM Corporation What is the Kafka protocol (the ‘wire’ API) ? • A set of Request/Response message pairs • e.g.: ProduceRequest, ProduceResponse (ApiKey=0) • A set of error codes • e.g.: Unknown Topic Or Partition (code=3) • Messages exchanged using Kafka’s own binary protocol • Over TCP (or TLS) • It’s not HTTP, AMQP, MQTT … • All requests initiated by the clients. • Brokers send Responses
- 5. © 2017 IBM Corporation Kafka’s TCP binary protocol • Open-source protocol (obviously!) • Messages defined in terms of Serializable data structures • Primitive types (intNN, nullable string) + Arrays • Struct types, e.g. RecordBatch for sequence of Records (key, value, metadata) • Clients typically holds multiple long-lived TCP connections • One per broker node • Clients expected to use non-blocking I/O http://kafka.apache.org/protocol
- 6. © 2017 IBM Corporation Kafka message capture with Wireshark $ bin/kafka-console-producer.sh --broker-list localhost:9092 --topic test
- 7. © 2017 IBM Corporation Anatomy of a wire message Magic 1 (v.0.10.x)
- 8. © 2017 IBM Corporation In 0.11 RecordBatch superseded MessageSet • Magic value = 2 • Records have Headers (KIP-82) • They look like footers 😀 • Metadata for Exactly-Once Semantics • Space savings for large batches https://cwiki.apache.org/confluence/display/KAFKA/A+Guide+To+The+ Kafka+Protocol#AGuideToTheKafkaProtocol-Messagesets
- 9. © 2017 IBM Corporation It’s an open Source protocol … … so anyone can write a client, in any language ? • In theory, yes • In practice, it’s a very big investment • A lot of intelligence goes in the client • Partitioning • Consumer Group assignment • Complexity has grown a lot since 0.8 … • Consumer group protocol • Security protocols/SASL mechanisms • KIP-4 (administrative actions) • Exactly-Once Semantics
- 10. © 2017 IBM Corporation The evolution of the Kafka API Kafka Version released # of API Keys (RPCs) # of Error Codes Including -1 UNKNOWN 0 NO_ERROR 0.7.2 Nov 2012 5 6 0.8.0 Nov 2013 8 13 0.9.0 Nov 2015 17 33 0.10.0 May 2016 19 37 0.10.2 Feb 2017 21 46 0.11.0 June 2017 33 55 • Brokers support older clients • Recent clients support somewhat older brokers
- 11. © 2017 IBM Corporation • Good support for the features of Apache Kafka • Message keys, committing offsets, exactly-once semantics, ... • Blending natural idioms of the language with proper use of Kafka • Solid software engineering • Responsive community support • Native code or ‘pure’ • Particularly important in the cloud • Does it support the technologies you have chosen to use? • Message encoding, Schema Registry, ... What makes for a good choice of client?
- 12. © 2017 IBM Corporation Project Language Pure or native code Apache Kafka client Java pure librdkafka C / C++ – node-kafka-native JavaScript (Node.js) native node-rdkafka JavaScript (Node.js) native confluent-kafka-go Go native Sarama Go pure kafkacat CLI / Shell scripts – Confluent Kafka REST Any – Let’s take a look at some different clients
- 13. © 2017 IBM Corporation Java producer • Part of Apache Kafka • Best for feature support and performance • Asynchronous with batching • Highly configurable • Rich metrics https://kafka.apache.org/0110/javadoc/index.html
- 14. © 2017 IBM Corporation • Part of Apache Kafka • Best for feature support and performance • Single-threaded • Polls for records and this is also a liveness check • Commits offsets automatically, async or sync Java consumer https://kafka.apache.org/0110/javadoc/index.html
- 15. © 2017 IBM Corporation C / C++ librdkafka • Fully featured native code Kafka client library • Portable so supports Linux, MacOS, Windows and more • Used as the basis for many other client libraries for other languages • Does a good job of keeping track with the Kafka releases • A bit tricky to build on platforms other than Linux if you want security • SASL only recently supported on Windows • SSL on Mac requires homebrew • Can emit metrics • At broker and topic-partition levels https://github.com/edenhill/librdkafka
- 16. © 2017 IBM Corporation • Concepts very similar to Apache Kafka client • But you have to manage memory yourself • Uses callbacks to report status but you have to poll to have them fire C librdkafka producer
- 17. © 2017 IBM Corporation • This is the low-level consumer interface • The high-level one supports consumer groups • Thread-safe (unlike Java) C librdkafka consumer
- 18. © 2017 IBM Corporation • Built on top of the C library • Looks more similar to Java, primarily because it’s object- oriented • Again, there’s a need to make a regular call to respond to callbacks C++ librdkafka consumer
- 19. © 2017 IBM Corporation • Another Node.js module wrapping librdkafka • Looked promising but ultimately not updated to keep up with new features • No updates for a long time now • Use node-rdkafka instead https://github.com/alfred-landrum/node-kafka-native JS node-kafka-native
- 20. © 2017 IBM Corporation • Third-party Node.js module wrapping librdkafka • Natural Node.js style of event delivery • A good example of the community working well https://github.com/Blizzard/node-rdkafka JS node-rdkafka producer
- 21. © 2017 IBM Corporation • Supports many of the features of consuming such as rebalancing, committing offsets • There’s also a streaming interface https://github.com/Blizzard/node-rdkafka JS node-rdkafka consumer
- 22. © 2017 IBM Corporation confluent-kafka-go producer • Confluent Go client based on librdkafka • Two variants of producer • Function-based • Channel-based • Delivery reports emitted on Events channel
- 23. © 2017 IBM Corporation • This variant of the API uses polling and then a type switch confluent-kafka-go consumer
- 24. © 2017 IBM Corporation • This variant of the API uses a channel to deliver messages and events such as rebalance confluent-kafka-go consumer
- 25. © 2017 IBM Corporation • Third-party pure Go client • Currently at 0.10.2.x level Go Sarama producer https://shopify.github.io/sarama/
- 26. © 2017 IBM Corporation • Consumer groups not supported yet • No offset tracking • Available as 3rd party extensions Go Sarama consumer https://shopify.github.io/sarama/
- 27. © 2017 IBM Corporation kafkacat https://github.com/edenhill/kafkacat • Command line non-JVM Kafka producer and consumer • Unsurprisingly, uses librdkafka too • Useful in shell scripts and just for trying stuff out on the command line
- 28. © 2017 IBM Corporation • Part of Confluent Platform • Integrated with Schema Registry • Use any language… • A bit tricky to format the data correctly Confluent Kafka REST https://github.com/confluentinc/kafka-rest
- 29. © 2017 IBM Corporation Do non-Java users face many issues? • Most problems are conceptual • Many new users struggle with the concepts of Kafka L • Users assume it’s the same as traditional messaging systems • Partitions, consumer groups, at-least-once semantics, ... • Documentation nowadays is getting really good • Historically, lack of best-practice examples in the various languages • Handling expected errors properly is a common theme • Failed commits, producer timeouts, ... • Non-Java clients lag behind Java in features • librdkafka doing a great job here, but dependent clients need to expose the features • Even more true for independent clients
- 30. © 2017 IBM Corporation Summary • Kafka has mature clients for several popular languages • Java still gives the best experience • librdkafka is delivering a solid base for non-Java clients • At the expense of native code • Some third-party ‘pure’ clients look good too • But the community support needs to stay the course
- 31. © 2017 IBM Corporation A few links Kafka Protocol http://kafka.apache.org/protocol https://cwiki.apache.org/confluence/display/KAFKA/A+Guide+To+The+Kafka+Protocol Kafka Clients directory https://cwiki.apache.org/confluence/display/KAFKA/Clients Code samples / modules https://github.com/ibm-messaging/message-hub-samples https://www.npmjs.com/package/message-hub-rest http://docs.confluent.io/current/clients/index.html
- 32. © 2017 IBM Corporation Q & A Contact us through the Summit App or via email ecomar@uk.ibm.com andrew_schofield@uk.ibm.com Thanks !