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Kafka Workshop

In this workshop, you'll learn how to build a simple Kafka producer-consumer application. This is the main documentation page and applies to all languages. Each language has a small, project-specific readme.

Pre-requisites

Backing Apps

Our local setup includes Kafka, a Postgres database, and a Kafka UI. To start them run ./scripts/start_services.sh.

  • Kafka UI: http://localhost:8080
  • Kafka broker: localhost:9092 (PLAINTEXT)
  • Postgres DB: postgres://postgres:password@localhost:5432/app (run ./scripts/psql_prompt.sh to run queries)
  • Schema Registry: required by kafka-ui (we won't be using it in this exercise)

Scripts

There are utility scripts in the ./scripts directory.

Script Name Description
create_topics.sh (re)create the order-status topic. Can also be done in UI (http://localhost:8080).
psql_prompt.sh opens a psql command prompt
db_query_order_status.sh queries the order_status table and outputs the results
db_truncate_order_status.sh truncates the order_status table
reset_services.sh alias for docker-compose down && docker-compose up -d - resets backing services (destructive)
start_services.sh alias for docker-compose up -d - starts backing services
stop_services.sh alias for docker-compose down -d -- stops backing services (destructive)

You can return to a clean slate by running ./scripts/reset_services.sh. This will clear all data from Kafka and Postgres and restart them.

Exercise

Objective

The goal of this workshop is to build a simple Kafka Producer-Consumer Data flow. We start with the Kafka producer that will publish 3,500 order status updates to the order-status table. After that we will build the consumer (postgres sink) that consumes the messages from kafka and writes the data to the Postgres database.

After running the consumer, you should see 500 records in the public.order_status table, all in the CLOSED status.

1. Building the Producer

Look for PRODUCER_START in the project of your choice. If you haven't already, start Kafka and all backing services.

  • ./scripts/start_services.sh - start Kafka, Kafka UI, and PostgresQL
  • ./scripts/create_topics.sh - create the order-status topic

Our Kafka producer will read order status updates from a txt file (./data/order-status-updates.txt, the scala project uses scala/src/main/resources/order-status-updates.txt) and publish each record to the order-status topic. The data looks like this:

{
  "id": "A3A25E64-CF72-4EB5-B387-C73E24DE02A2",
  "accountId": "acct_0",
  "status": "IN_PROCESS",
  "timestamp": "2023-05-11T20:05:07.225Z"
}
{
  "id": "A3A25E64-CF72-4EB5-B387-C73E24DE02A2",
  "accountId": "acct_0",
  "status": "PENDING",
  "timestamp": "2023-05-11T20:05:06.225Z"
}

2. Building Consumer (Postgres Sink)

Next build the kafka consumer. Look for CONSUMER_START in the project of your choice. The consumer is responsible for reading from the order-status topic and writing the messages to the public.order_status table. It uses a consumer group (order-status-consumer) to track offsets and to allow for multiple instances to run in parallel. See the project docs for how to run multiple instance.

Each record in the table should correspond to an order status insert or update (no deletes). The table is keyed off the order id, so each update for a given order id will overwrite the previous row for that id.

Note: the consumers don't stop, you can see whether it's processed all records by looking at the consumer group () in the kafka ui (http://localhost:8080). Add some logging so you know it's working. Check the consumer group in the kafka UI to see if it has processed all records.

Completion

Once you have completed both parts of the exercise, you should be able to run the producer to publish messages to Kafka, and then run the consumer to consume those messages and write them to the Postgres database.

When the public.order_status table contains 500 records, and all of them are in the "CLOSED" status, you have successfully completed the workshop.

Good luck, and have fun learning about Kafka, producers, consumers!

Troubleshooting

If you run into any issues:

  • Use ./scripts/reset_services.sh to clear all data from Kafka and Postgres and start over.
  • Double-check that all services are running. Run docker-compose ps and see if anything is (exited). Use docker-compose logs (kafka1|postgres|akfka-ui|zookeeper) to see what You can use the ./scripts/start_services.sh command to start all services.
  • Make sure your messages are correctly formatted and that the order-status topic exists.

If you're still having trouble, don't hesitate to ask for help.

Docker Install

If you don't have docker installed, the following will install Colima.

brew install colima docker docker-compose docker-buildx

mkdir -p ~/.docker/cli-plugins
ln -sfn $(brew --prefix)/opt/docker-compose/bin/docker-compose ~/.docker/cli-plugins/docker-compose

colima start --cpu 2 --memory 6 --disk 80