##Objectives
-
Demonstrate microservices connected via Kafka
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Demonstrate schema evolution via AVRO
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Demonstrate bi-directional messages from websockets to kafka and vice-versa
The app exposes a /cars REST endpoint capable of receiving a JSON message via HTTP POST. Below example, shows POST via curl and the car schema
curl -i -H "Content-Type: application/json" -X POST -d '{"year":"2014","make":"toyota19","model":"something cool","engine":"2.67"}' http://<<DOCKER_HOST_IP>>:8080/cars
In my case, i am running docker-machine on OS X, hence the typical DOCKER_HOST_IP would be 192.168.99.100. If you are running docker directly on linux, it would probably be 127.0.0.1
The REST endpoint in turn publishes the AVRO version of that message to the kafka topic called "avroautos". Another service, picks up the AVRO message and logs it to the console in JSON format.
Avro was chosen primarily due to schema evolution features.
To demonstrate bi-directional messages from websockets, a user-agent sends carIDs(aka activity event) that it would like to track via websockets to a destination "/app/activity" and the user-agent subscribes to a topic called "/topic/tracker". On server side, the server timestamp is added to every activity event and message is routed to a kafka topic called "cartracker". Then a java component subscribes to the "cartracker" topic and dispatches the event to SimpleMessageRouter,which in turn broadcasts the message to all subscribed user-agents.
To access UI for websockets:
- Direct your browser to
http://<<DOCKER_HOST_IP>>:8080/index.html - Press connect
- Send car identifier
- Browser displays the message from kafka
The websockets endpoint for protocol upgrade is /websocket
To compile the application, cd to the application root folder and issue : ./gradlew build
To run the application:
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If you are not running docker version, first start zookeeper and kafka. Then run the application via command
java -jar build/libs/demo-0.0.1-SNAPSHOT.jar -
If you are running via docker, simply issue:
docker-compose up --build. This will start one container for zookeeper, other for kafka and yet another for demo application. -
To view docker images:
docker images -
To view docker containers:
docker ps -a -
You can run each docker image as standalone and get access to bash shell to view environment variables. Another way to view environment variables for running containers is through the command
docker inspect --format '{{ .Config.Env }}'