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Avro message with Kafka connector example

Given below is a sample scenario that demonstrates how to send Apache Avro messages to a Kafka broker via Kafka topics. The publishMessages operation allows you to publish messages to the Kafka brokers via Kafka topics.

What you'll build

Given below is a sample API that illustrates how you can connect to a Kafka broker with the init operation and then use the publishMessages operation to publish messages via the topic. It exposes Kafka functionalities as a RESTful service. Users can invoke the API using HTTP/HTTPS with the required information.

API has the /publishMessages context. It publishes messages via the topic to the Kafka server.

Set up Kafka

Before you begin, set up Kafka by following the instructions in Setting up Kafka.

Set up the integration project

Follow the steps in the create integration project guide to set up the Integration Project.

Create the integration logic

  1. Click + on the Extension panel APIs to create the REST API.

  2. Specify the API name as KafkaTransport and API context as /publishMessages. Click create.

Adding a Rest API

  1. Click the /resource default endpoint to open the Resource View. Then click the + arrow below the Start node to open the side panel. Select Externals and click Add new Connection. Search kafkaTransport and click. Adding a kafka Connection
  2. Provide values as below and click Add.
    • Connection Name - Sample_Kafka
    • Connection Type - kafka
    • Boostrap Servers - localhost:9092
    • Key Serializer Class - io.confluent.kafka.serializers.KafkaAvroSerializer
    • Value Serializer Class - io.confluent.kafka.serializers.KafkaAvroSerializer
    • Schema Registry URL - http://localhost:8081
    • Max Pool Size - 100

Create a kafka Connection 5. You can go to the XML configuration of the API (source view) and copy the following configuration. 

<?xml version="1.0" encoding="UTF-8"?>
<api context="/publishMessages" name="KafkaTransport" xmlns="http://ws.apache.org/ns/synapse">
    <resource methods="POST" uri-template="/">
        <inSequence>
            <property name="valueSchema" expression="json-eval($.test)" scope="default" type="STRING"/>
            <property name="value" expression="json-eval($.value)" scope="default" type="STRING"/>
            <property name="key" expression="json-eval($.key)" scope="default" type="STRING"/>
            <property name="topic" expression="json-eval($.topic)" scope="default" type="STRING"/>
            <kafkaTransport.publishMessages configKey="Sample_Kafka">
                <topic>{$ctx:topic}</topic>
                <partitionNo>0</partitionNo>
                <key>{$ctx:key}</key>
                <value>{$ctx:value}</value>
                <valueSchema>{$ctx:valueSchema}</valueSchema>
                <keySchemaSoftDeleted>false</keySchemaSoftDeleted>
                <valueSchemaSoftDeleted>false</valueSchemaSoftDeleted>
            </kafkaTransport.publishMessages>
        </inSequence>
    </resource>
</api>

Deployment

Follow these steps to deploy the exported CApp in the Enterprise Integrator Runtime.

Deploying on Micro Integrator To deploy and run the project, refer to the Build and Run guide.

Test

Invoke the API (http://localhost:8290/publishMessages) with the following payload,

{
   "test": {
       "type": "record",
       "name": "myrecord",
       "fields": [
           {
               "name": "f1",
               "type": ["string", "int"]
           }
       ]
   },
   "value": {
       "f1": "sampleValue"
   },
   "key": "sampleKey",
   "topic": "myTopic"
}

Info

Refer to the confluent documentation for installing confluent.

Run the following command to verify the messages: 

[confluent_home]/bin/kafka-avro-console-consumer.sh --topic myTopic --bootstrap-server localhost:9092 --property print.key=true --from-beginning
See the following message content: 
{"f1":{"string":"sampleValue"}}
Sample Connection configuration when the Confluent Schema Registry is secured with basic auth

<?xml version="1.0" encoding="UTF-8"?>
    <localEntry key="Sample_Kafka" xmlns="http://ws.apache.org/ns/synapse">
        <kafkaTransport.init>
            <connectionType>kafka</connectionType>
            <name>Sample_Kafka2</name>
            <bootstrapServers>localhost:9092</bootstrapServers>
            <keySerializerClass>io.confluent.kafka.serializers.KafkaAvroSerializer</keySerializerClass>
            <valueSerializerClass>io.confluent.kafka.serializers.KafkaAvroSerializer</valueSerializerClass>
            <schemaRegistryUrl>http://localhost:8081</schemaRegistryUrl>
            <basicAuthCredentialsSource>USER_INFO</basicAuthCredentialsSource>
            <basicAuthUserInfo>admin:admi</basicAuthUserInfo>
            <maxPoolSize>100</maxPoolSize>
            <poolingEnabled>false</poolingEnabled>
        </kafkaTransport.init>
    </localEntry>
In the above example, the basicAuthCredentialsSource parameter is configured as USER_INFO. For example, consider a scenario where the basicAuthCredentialsSource parameter is set to URL as follows:

<basicAuthCredentialsSource>URL</basicAuthCredentialsSource>

Then, the schemaRegistryUrl parameter should be configured as shown below.

<schemaRegistryUrl>http://admin:admin@localhost:8081</schemaRegistryUrl>
Refer to the confluent documentation for more details.

This demonstrates how the Kafka connector publishes Avro messages to Kafka brokers.

What's next