Deploying to Kafka

Simple Sourcing is a library that makes use of Kafka Streams. It does not need to be deployed separately - it runs in process as part of your application.

The minimum viable Simple Sourcing deployment consists of the following:

  • A Zookeeper instance
  • 3 or more Kafka broker instances
  • If using Avro serialization, an instance of the Confluent Schema registry

See the auction example app for an example docker configuration.

Inspecting data in Kafka

It can be useful to see the data contained in the topics to understand the data structures used and to validate correctness.

To see a list of available topics

docker-compose exec broker kafka-topics --zookeeper zookeeper:2181 --list

To see what data is available in a given topic

docker-compose exec broker kafka-run-class \
  --offsets 10 --broker-list broker:9092 \
  --topic simple-events

This outputs one line per topic partition in the following format

<TOPICNAME> : <PARTITION> : Highest offset in latest log file [ highest offset in rest of log files ] [ , earliest offset held of oldest log file ]

To see the contents of the event source topic from the beginning if using Avro

docker-compose exec schema_registry kafka-avro-console-consumer \
  --bootstrap-server broker:9092 \
  --property schema.registry.url=http://schema_registry:8081 \
  --property print.key=true \
  --from-beginning \
  --topic simple-events

If using text-based encodings like JSON you can use

docker-compose exec broker kafka-console-consumer \
  --bootstrap-server broker:9092 \
  --property print.key=true \
  --from-beginning \
  --topic simple-events

The Simple Sourcing example repo also consists of scripts to perform these tasks on a running docker stack.