Exercise 3

In this exercise, we'll turn our model (png | json) into code to run our system on the Streaming Data Platform. The Event Model will guide our creation of Domain Transfer Objects, Domain Types, and our Decide and Evolve functions. Finally, we'll wire these code components into the Kafka Producer and Streams APIs.

Exercise Instructions

Each step has its own directory containing a README with instructions, and with tests that initially fail.

First, we'll follow the Event Model as a guide to defining some Command, Event, and Read Model transfer types using Protocol Buffers. See the Step 1 README for details.
Then, we'll define a selection of the domain types that correspond to our transfer types, but which enforce more of the business constraints. We'll also define mapping functions to convert between transfer and domain types. See the Step 2 README for details.
Next, we'll implement Decide and Evolve on our domain types. We'll also expose these methods, as well as defining React, as pure Domain Functions defined in terms of our transfer types. These Domain Functions fully encapsulate the business logic of our bounded contexts: Rides and Vehicles. See the Step 3 README for details.
Finally, we'll wire up our Decide function to a Kafka Producer, and our Evolve function to a Kafka Streams topology. See the Step 4 README for details.

Running the Final App

The final app code (no peeking!) is in final/. The app must be configured to run with a Kafka cluster, and you can do this in one of two ways.

Running with Confluent Cloud

To run with a Confluent Cloud Kafka cluster, first sign up for a Confluent Cloud account. Then create a cluster and download the configuration file. Export the values in the configuration file as the following environment variables before running the app:

export KAFKA_BOOTSTRAP_SERVERS=[from config file]
export KAFKA_SECURITY_PROTOCOL=SASL_SSL
export KAFKA_SASL_JAAS_CONFIG='org.apache.kafka.common.security.plain.PlainLoginModule required username="[from config file]" password="[from config file]";'
export KAFKA_SASL_MECHANISM=PLAIN
export KAFKA_SCHEMA_REGISTRY_URL=[confluent cloud schema registry]
./gradlew :final:run

Running with local Kafka via Docker Stack

Run locally using:

docker-compose up -d
./gradlew :final:run

To clean up the docker-compose stack that runs our Kafka and Schema Registry:

docker-compose down