Node.js: Code Example for Apache Kafka®¶

In this tutorial, you will run a Node.js client application 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¶

Node.js version 8.6 or higher installed on your local machine.
Users of macOS 10.13 (High Sierra) and later should read node-rdkafka’s additional configuration instructions related to OpenSSL before running npm install.
OpenSSL version 1.0.2.

Kafka Cluster¶

You can use this tutorial with a Kafka cluster in any environment:
- In Confluent Cloud
- On your local host
- Any remote Kafka cluster
If you are running on Confluent Cloud, you must have access to a Confluent Cloud cluster with an API key and secret.
- The first 20 users to sign up for Confluent Cloud and use promo code C50INTEG will receive an additional $50 free usage (details)
- For an automated way to create a Kafka cluster, credentials, and ACLs in Confluent Cloud, see ccloud-stack Utility for Confluent Cloud.

Setup¶

Clone the confluentinc/examples GitHub repository and check out the 6.1.0-post branch.

git clone https://github.com/confluentinc/examples
cd examples
git checkout 6.1.0-post

Change directory to the example for Node.js.
```
cd clients/cloud/nodejs/
```
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
```
# Kafka
bootstrap.servers={{ BROKER_ENDPOINT }}
security.protocol=SASL_SSL
sasl.mechanisms=PLAIN
sasl.username={{ CLUSTER_API_KEY }}
sasl.password={{ CLUSTER_API_SECRET }}
```
- 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 npm dependencies.
```
npm install
```
Run the producer, passing in arguments for:
- the local file with configuration parameters to connect to your Kafka cluster
- the topic name
```
node producer.js -f $HOME/.confluent/librdkafka.config -t test1
```

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

Created 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}
Successfully produced record to topic "test1" partition 0 {"count":0}
Successfully produced record to topic "test1" partition 0 {"count":1}
Successfully produced record to topic "test1" partition 0 {"count":2}
Successfully produced record to topic "test1" partition 0 {"count":3}
Successfully produced record to topic "test1" partition 0 {"count":4}
Successfully produced record to topic "test1" partition 0 {"count":5}
Successfully produced record to topic "test1" partition 0 {"count":6}
Successfully produced record to topic "test1" partition 0 {"count":7}
Successfully produced record to topic "test1" partition 0 {"count":8}
Successfully produced record to topic "test1" partition 0 {"count":9}

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
```
node consumer.js -f $HOME/.confluent/librdkafka.config -t test1
```

Verify the consumer received all the messages:

Consuming messages from test1
Consumed record with key alice and value {"count":0} of partition 0 @ offset 0. Updated total count to 1
Consumed record with key alice and value {"count":1} of partition 0 @ offset 1. Updated total count to 2
Consumed record with key alice and value {"count":2} of partition 0 @ offset 2. Updated total count to 3
Consumed record with key alice and value {"count":3} of partition 0 @ offset 3. Updated total count to 4
Consumed record with key alice and value {"count":4} of partition 0 @ offset 4. Updated total count to 5
Consumed record with key alice and value {"count":5} of partition 0 @ offset 5. Updated total count to 6
Consumed record with key alice and value {"count":6} of partition 0 @ offset 6. Updated total count to 7
Consumed record with key alice and value {"count":7} of partition 0 @ offset 7. Updated total count to 8
Consumed record with key alice and value {"count":8} of partition 0 @ offset 8. Updated total count to 9
Consumed record with key alice and value {"count":9} of partition 0 @ offset 9. Updated total count to 10

View the consumer code.