Create an Apache Kafka Client App for Ruby¶

In this tutorial, you will run a Ruby client application using the rdkafka gem that produces messages to and consumes messages from an Apache Kafka® cluster.

After you run the tutorial, use the provided source code as a reference to develop your own Kafka client application.

Prerequisites¶

Client¶

Bundler installed on your machine. Install using gem install bundler.

Kafka Cluster¶

The easiest way to follow this tutorial is with Confluent Cloud because you don’t have to run a local Kafka cluster. From the Console, click on LEARN to provision a cluster and click on Clients to get the cluster-specific configurations and credentials to set for your client application.

You can alternatively use the supported CLI or REST API, or the community-supported ccloud-stack utility for Confluent Cloud.

If you don’t want to use Confluent Cloud, you can also use this tutorial with a Kafka cluster running on your local host or any other remote server.

Setup¶

Clone the confluentinc/examples GitHub repository and check out the 7.4.8-post branch.

git clone https://github.com/confluentinc/examples
cd examples
git checkout 7.4.8-post

Change directory to the example for Ruby.
```
cd clients/cloud/ruby/
```
Create a local file (for example, at $HOME/.confluent/librdkafka.config) with configuration parameters to connect to your Kafka cluster. Starting with one of the templates below, customize the file with connection information to your cluster. Substitute your values for {{ BROKER_ENDPOINT }}, {{CLUSTER_API_KEY }}, and {{ CLUSTER_API_SECRET }} (see Configure Confluent Cloud Clients for instructions on how to manually find these values, or use the ccloud-stack utility for Confluent Cloud to automatically create them).
- Template configuration file for Confluent Cloud
```
# Required connection configs for Kafka producer, consumer, and admin
bootstrap.servers={{ BROKER_ENDPOINT }}
security.protocol=SASL_SSL
sasl.mechanisms=PLAIN
sasl.username={{ CLUSTER_API_KEY }}
sasl.password={{ CLUSTER_API_SECRET }}

# Best practice for higher availability in librdkafka clients prior to 1.7
session.timeout.ms=45000
```
- Template configuration file for local host
```
# Kafka
bootstrap.servers=localhost:9092
```

Basic Producer and Consumer¶

In this example, the producer application writes Kafka data to a topic in your Kafka cluster. If the topic does not already exist in your Kafka cluster, the producer application will use the Kafka Admin Client API to create the topic. Each record written to Kafka has a key representing a username (for example, alice) and a value of a count, formatted as json (for example, {"count": 0}). The consumer application reads the same Kafka topic and keeps a rolling sum of the count as it processes each record.

Produce Records¶

Install gems:
```
bundle install
```
Run the producer, passing in arguments for:
- the local file with configuration parameters to connect to your Kafka cluster
- the topic name
```
ruby producer.rb -f $HOME/.confluent/librdkafka.config --topic test1
```

Verify the producer sent all the messages. You should see:

Creating topic test1
Producing record: alice {"count":0}
Producing record: alice {"count":1}
Producing record: alice {"count":2}
Producing record: alice {"count":3}
Producing record: alice {"count":4}
Producing record: alice {"count":5}
Producing record: alice {"count":6}
Producing record: alice {"count":7}
Producing record: alice {"count":8}
Producing record: alice {"count":9}
10 messages were successfully produced to topic test1!

View the producer code.

Consume Records¶

Run the consumer, passing in arguments for:
- the local file with configuration parameters to connect to your Kafka cluster
- the topic name you used earlier
```
ruby consumer.rb -f $HOME/.confluent/librdkafka.config --topic test1
```

Verify the consumer received all the messages:

Consuming messages from test1
Consumed record with key alice and value {"count":0}, and updated total count 0
Consumed record with key alice and value {"count":1}, and updated total count 1
Consumed record with key alice and value {"count":2}, and updated total count 3
Consumed record with key alice and value {"count":3}, and updated total count 6
Consumed record with key alice and value {"count":4}, and updated total count 10
Consumed record with key alice and value {"count":5}, and updated total count 15
Consumed record with key alice and value {"count":6}, and updated total count 21
Consumed record with key alice and value {"count":7}, and updated total count 28
Consumed record with key alice and value {"count":8}, and updated total count 36
Consumed record with key alice and value {"count":9}, and updated total count 45
...

View the consumer code.