Apache Kafka® CLI : Command Example¶

In this tutorial, you will run Apache Kafka® commands that produce 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¶

Download Confluent Platform 6.2.0

Kafka Cluster¶

The easiest way to follow this tutorial is with Confluent Cloud because you don’t have to run a local Kafka cluster. When you sign up for Confluent Cloud, apply promo code C50INTEG to receive an additional $50 free usage (details). 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 6.2.0-post branch.

git clone https://github.com/confluentinc/examples
cd examples
git checkout 6.2.0-post

Change directory to the example for Apache Kafka® commands.
```
cd clients/cloud/kafka-commands/
```
Create a local file (for example, at $HOME/.confluent/java.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.jaas.config=org.apache.kafka.common.security.plain.PlainLoginModule required username='{{ CLUSTER_API_KEY }}' password='{{ CLUSTER_API_SECRET }}';
sasl.mechanism=PLAIN
# Required for correctness in Apache Kafka clients prior to 2.6
client.dns.lookup=use_all_dns_ips

# Best practice for Kafka producer to prevent data loss 
acks=all
```
- 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¶

Create the Kafka topic.

kafka-topics \
   --bootstrap-server `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --command-config $HOME/.confluent/java.config \
   --topic test1 \
   --create \
   --replication-factor 3 \
   --partitions 6

Run the kafka-console-producer command, writing messages to topic test1, passing in arguments for:

--property parse.key=true --property key.separator=,: pass key and value, separated by a comma

kafka-console-producer \
   --topic test1 \
   --broker-list `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --property parse.key=true \
   --property key.separator=, \
   --producer.config $HOME/.confluent/java.config

At the > prompt, type a few messages, using a , as the separator between the message key and value:
```
alice,{"count":0}
alice,{"count":1}
alice,{"count":2}
```
When you are done, press CTRL-D.
View the producer code.

Consume Records¶

Run the kafka-console-consumer command, reading messages from topic test1, passing in additional arguments for:

--property print.key=true: print key and value (by default, it only prints value)
--from-beginning: print all messages from the beginning of the topic

kafka-console-consumer \
   --topic test1 \
   --bootstrap-server `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --property print.key=true \
   --from-beginning \
   --consumer.config $HOME/.confluent/java.config

You should see the messages you typed in step 3.

alice   {"count":0}
alice   {"count":1}
alice   {"count":2}

When you are done, press CTRL-C.
View the consumer code.

Avro and Confluent Cloud Schema Registry¶

This example is similar to the previous example, except the value is formatted as Avro and integrates with the Confluent Cloud Schema Registry. Before using Confluent Cloud Schema Registry, check its availability and limits.

As described in the Quick Start for Schema Management on Confluent Cloud in the Confluent Cloud Console, enable Confluent Cloud Schema Registry and create an API key and secret to connect to it.
Verify that your VPC can connect to the Confluent Cloud Schema Registry public internet endpoint.

Update your local configuration file (for example, at $HOME/.confluent/java.config) with parameters to connect to Schema Registry.

Template configuration file for Confluent Cloud

# Required connection configs for Kafka producer, consumer, and admin
bootstrap.servers={{ BROKER_ENDPOINT }}
security.protocol=SASL_SSL
sasl.jaas.config=org.apache.kafka.common.security.plain.PlainLoginModule required username='{{ CLUSTER_API_KEY }}' password='{{ CLUSTER_API_SECRET }}';
sasl.mechanism=PLAIN
# Required for correctness in Apache Kafka clients prior to 2.6
client.dns.lookup=use_all_dns_ips

# Best practice for Kafka producer to prevent data loss 
acks=all

# Required connection configs for Confluent Cloud Schema Registry
schema.registry.url=https://{{ SR_ENDPOINT }}
basic.auth.credentials.source=USER_INFO
basic.auth.user.info={{ SR_API_KEY }}:{{ SR_API_SECRET }}

Template configuration file for local host

# Kafka
bootstrap.servers=localhost:9092

# Confluent Schema Registry
schema.registry.url=http://localhost:8081

Verify your Confluent Cloud Schema Registry credentials by listing the Schema Registry subjects. In the following example, substitute your values for {{ SR_API_KEY }}, {{ SR_API_SECRET }}, and {{ SR_ENDPOINT }}.
```
curl -u {{ SR_API_KEY }}:{{ SR_API_SECRET }} https://{{ SR_ENDPOINT }}/subjects
```

Produce Avro Records¶

Create the topic in Confluent Cloud.

kafka-topics \
   --bootstrap-server `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --command-config $HOME/.confluent/java.config \
   --topic test2 \
   --create \
   --replication-factor 3 \
   --partitions 6

Run the kafka-avro-console-producer command, writing messages to topic test2, passing in arguments for:

--property value.schema: define the schema
--property schema.registry.url: connect to the Confluent Cloud Schema Registry endpoint https://<SR ENDPOINT>
--property basic.auth.credentials.source: specify USER_INFO
--property schema.registry.basic.auth.user.info: <SR API KEY>:<SR API SECRET>

Important

You must pass in the additional Schema Registry parameters as properties instead of a properties file due to https://github.com/confluentinc/schema-registry/issues/1052.

kafka-avro-console-producer \
   --topic test2 \
   --broker-list `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --producer.config $HOME/.confluent/java.config \
   --property value.schema='{"type":"record","name":"myrecord","fields":[{"name":"count","type":"int"}]}' \
   --property schema.registry.url=https://<SR ENDPOINT> \
   --property basic.auth.credentials.source=USER_INFO \
   --property schema.registry.basic.auth.user.info='<SR API KEY>:<SR API SECRET>'

# Same as above, as a single bash command to parse the values out of $HOME/.confluent/java.config
kafka-avro-console-producer \
   --topic test2 \
   --broker-list `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --producer.config $HOME/.confluent/java.config \
   --property value.schema='{"type":"record","name":"myrecord","fields":[{"name":"count","type":"int"}]}' \
   --property schema.registry.url=$(grep "^schema.registry.url" $HOME/.confluent/java.config | cut -d'=' -f2) \
   --property basic.auth.credentials.source=USER_INFO \
   --property schema.registry.basic.auth.user.info=$(grep "^schema.registry.basic.auth.user.info" $HOME/.confluent/java.config | cut -d'=' -f2)

At the > prompt, type a few messages:
```
{"count":0}
{"count":1}
{"count":2}
```
When you are done, press CTRL-D.
View the producer Avro code.

Consume Avro Records¶

Run the kafka-avro-console-consumer command, reading messages from topic test, passing in arguments for: The additional Schema Registry parameters are required to be passed in as properties instead of a properties file due to https://github.com/confluentinc/schema-registry/issues/1052.

--property schema.registry.url: connect to the Confluent Cloud Schema Registry endpoint https://<SR ENDPOINT>
--property basic.auth.credentials.source: specify USER_INFO
--property schema.registry.basic.auth.user.info: <SR API KEY>:<SR API SECRET>

Important

You must pass in the additional Schema Registry parameters as properties instead of a properties file due to https://github.com/confluentinc/schema-registry/issues/1052.

kafka-avro-console-consumer \
   --topic test2 \
   --from-beginning \
   --bootstrap-server `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --consumer.config $HOME/.confluent/java.config \
   --property schema.registry.url=https://<SR ENDPOINT> \
   --property basic.auth.credentials.source=USER_INFO \
   --property schema.registry.basic.auth.user.info='<SR API KEY>:<SR API SECRET>'

Same as above, as a single bash command to parse the values out of $HOME/.confluent/java.config
kafka-avro-console-consumer \
   --topic test2 \
   --from-beginning \
   --bootstrap-server `grep "^\s*bootstrap.server" $HOME/.confluent/java.config | tail -1` \
   --consumer.config $HOME/.confluent/java.config \
   --property schema.registry.url=$(grep "^schema.registry.url" $HOME/.confluent/java.config | cut -d'=' -f2) \
   --property basic.auth.credentials.source=USER_INFO \
   --property schema.registry.basic.auth.user.info=$(grep "^schema.registry.basic.auth.user.info" $HOME/.confluent/java.config | cut -d'=' -f2)

You should see the messages you typed earlier.

{"count":0}
{"count":1}
{"count":2}

When you are done, press CTRL-C.
View the consumer Avro code.