Kafka connect is sending a malformed json

问题

I'm trying to perform a proof of concept using kafka-connect with a rabbitMQ connector. Basically, I have two simple spring boot applications; a RabbitMQ producer and a Kafka consumer. The consumer can not handle the messages from the connector because it's transforming somehow my JSON message; RabbitMQ sends {"transaction": "PAYMENT", "amount": "$125.0"} and kafka-connect prints X{"transaction": "PAYMENT", "amount": "$125.0"}. Please note the X at the beginning. If I add a field, let's say "foo": "bar" then that letter becomes a t or whatever.

Dockerfile (connector):

FROM confluentinc/cp-kafka-connect-base:5.3.2
RUN confluent-hub install --no-prompt confluentinc/kafka-connect-rabbitmq:latest

Please generate the image as follows: docker build . -t rabbit-connector, so you can reference it in the docker-compose file as rabbit-connector.

docker-compose.yml:

version: '2'

networks:
  kafka-connect-network:
    driver: bridge

services:
  zookeeper:
    image: confluentinc/cp-zookeeper:5.3.2
    networks: 
      - kafka-connect-network
    ports:
      - '31000:31000'
    environment:
      ZOOKEEPER_CLIENT_PORT: 2181
      ZOOKEEPER_TICK_TIME: 2000
      KAFKA_JMX_HOSTNAME: "localhost"
      KAFKA_JMX_PORT: 31000

  kafka:
    image: confluentinc/cp-enterprise-kafka:5.3.2
    networks: 
      - kafka-connect-network
    ports:
      - '9092:9092'
      - '31001:31001'
    depends_on:
      - zookeeper
    environment:
      KAFKA_BROKER_ID: 1
      KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT
      KAFKA_INTER_BROKER_LISTENER_NAME: PLAINTEXT
      KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://kafka:29092,PLAINTEXT_HOST://localhost:9092
      KAFKA_AUTO_CREATE_TOPICS_ENABLE: "true"
      KAFKA_METRIC_REPORTERS: io.confluent.metrics.reporter.ConfluentMetricsReporter
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 100
      CONFLUENT_METRICS_REPORTER_BOOTSTRAP_SERVERS: kafka:29092
      CONFLUENT_METRICS_REPORTER_ZOOKEEPER_CONNECT: zookeeper:2181
      CONFLUENT_METRICS_REPORTER_TOPIC_REPLICAS: 1
      CONFLUENT_METRICS_ENABLE: 'false'
      CONFLUENT_SUPPORT_CUSTOMER_ID: 'anonymous'
      KAFKA_JMX_HOSTNAME: "localhost"
      KAFKA_JMX_PORT: 31001

  schema-registry:
    image: confluentinc/cp-schema-registry:5.3.2
    depends_on:
      - zookeeper
      - kafka
    networks: 
      - kafka-connect-network
    ports:
      - '8081:8081'
      - '31002:31002'
    environment:
      SCHEMA_REGISTRY_HOST_NAME: schema-registry
      SCHEMA_REGISTRY_KAFKASTORE_CONNECTION_URL: zookeeper:2181
      SCHEMA_REGISTRY_JMX_HOSTNAME: "localhost"
      SCHEMA_REGISTRY_JMX_PORT: 31002

  rabbitmq:
    image: rabbitmq
    environment:
      RABBITMQ_DEFAULT_USER: guest
      RABBITMQ_DEFAULT_PASS: guest
      RABBITMQ_DEFAULT_VHOST: "/"
    networks: 
      - kafka-connect-network
    ports:
      - '15672:15672'
      - '5672:5672'

  kafka-connect:
    image: rabbit-connector
    networks: 
      - kafka-connect-network
    ports:
      - '8083:8083'
      - '31004:31004'
    environment:
      CONNECT_BOOTSTRAP_SERVERS: "kafka:29092"
      CONNECT_REST_PORT: 8083
      CONNECT_GROUP_ID: compose-connect-group
      CONNECT_CONFIG_STORAGE_TOPIC: docker-connect-configs
      CONNECT_OFFSET_STORAGE_TOPIC: docker-connect-offsets
      CONNECT_STATUS_STORAGE_TOPIC: docker-connect-status
      CONNECT_KEY_CONVERTER: org.apache.kafka.connect.storage.StringConverter
      CONNECT_VALUE_CONVERTER: io.confluent.connect.avro.AvroConverter
      CONNECT_VALUE_CONVERTER_SCHEMA_REGISTRY_URL: 'http://schema-registry:8081'
      CONNECT_INTERNAL_KEY_CONVERTER: "org.apache.kafka.connect.json.JsonConverter"
      CONNECT_INTERNAL_VALUE_CONVERTER: "org.apache.kafka.connect.json.JsonConverter"
      CONNECT_REST_ADVERTISED_HOST_NAME: "kafka-connect"
      CONNECT_LOG4J_ROOT_LOGLEVEL: "ERROR"
      CONNECT_LOG4J_LOGGERS: "org.apache.kafka.connect.runtime.rest=WARN,org.reflections=ERROR"
      CONNECT_CONFIG_STORAGE_REPLICATION_FACTOR: "1"
      CONNECT_OFFSET_STORAGE_REPLICATION_FACTOR: "1"
      CONNECT_STATUS_STORAGE_REPLICATION_FACTOR: "1"
      CONNECT_PLUGIN_PATH: /usr/share/java,/usr/share/confluent-hub-components
      KAFKA_JMX_HOSTNAME: "localhost"
      KAFKA_JMX_PORT: 31004
    depends_on:
      - zookeeper
      - kafka
      - schema-registry
      - rabbitmq

  rest-proxy:
    image: confluentinc/cp-kafka-rest:5.3.2
    depends_on:
      - zookeeper
      - kafka
      - schema-registry
    networks: 
      - kafka-connect-network
    ports:
      - '8082:8082'
      - '31005:31005'
    environment:
      KAFKA_REST_HOST_NAME: rest-proxy
      KAFKA_REST_BOOTSTRAP_SERVERS: 'kafka:29092'
      KAFKA_REST_LISTENERS: "http://0.0.0.0:8082"
      KAFKA_REST_SCHEMA_REGISTRY_URL: 'http://schema-registry:8081'
      KAFKAREST_JMX_HOSTNAME: "localhost"
      KAFKAREST_JMX_PORT: 31005

schema.avsc:

{
  "type": "record",
  "name": "CustomMessage",
  "namespace": "com.poc.model",
  "fields": [
    {
      "name": "transaction",
      "type": "string"
    },
    {
      "name": "amount",
      "type": "string"
    }
  ]
}

So here I am using a StringConverter for my key (which I don't care to be honest) and AvroConverter for the value. Maybe I am missing something or I'm misconfiguring my kafka-connect worker.

My connector configuration is (connector-config.json):

 {
   "name" : "rabbit_to_kafka_poc",
   "config" : {
    "connector.class" : "io.confluent.connect.rabbitmq.RabbitMQSourceConnector",
    "tasks.max" : "1",
    "key.converter":"org.apache.kafka.connect.storage.StringConverter",
    "value.converter": "io.confluent.connect.avro.AvroConverter",
    "value.converter.schema.registry.url": "http://schema-registry:8081",
    "kafka.topic" : "spectrum-message",
    "rabbitmq.queue" : "spectrum-queue",
    "rabbitmq.username": "guest",
    "rabbitmq.password": "guest",
    "rabbitmq.host": "rabbitmq",
    "rabbitmq.port": "5672",
    "rabbitmq.virtual.host": "/"
   } 
 }

To register my connector I do curl -i -X POST -H "Accept:application/json" -H "Content-Type:application/json" http://localhost:8083/connectors/ -d @connector-config.json.

Once I configure everything, I run the following command to print out my messages:

kafka-avro-console-consumer --bootstrap-server localhost:9092 \
                            --topic spectrum-message \
                            --from-beginning

And the JSON starts with a letter, so my question is why is this happening? I think something is encoding my message but my rabbitMQ producer is sending a plain JSON message. I can confirm by testing with a RabbitMQ consumer and debugging my application to the point where the message is being sent out.

回答1:

You need to use the ByteArrayConverter. It's just bytes that the connector pulls from RabbitMQ - it won't try to coerce it to a schema. Even if you serialise it to Avro, the schema is just a single field of bytes:

$ curl -s -XGET localhost:8081/subjects/rabbit-test-avro-00-value/versions/1 | jq '.'
{
  "subject": "rabbit-test-avro-00-value",
  "version": 1,
  "id": 1,
  "schema": "\"bytes\""
}

If you want to write it to a topic in Avro (which is a good idea) with a schema then use something like Kafka Streams or ksqlDB to do this, applying a stream processor to the source topic which Kafka Connect writes to with the ByteArrayConverter.

For example in ksqlDB you would do:

-- Inspect the topic - ksqlDB recognises the format as JSON

ksql> PRINT 'rabbit-test-00' FROM BEGINNING;
Format:JSON
{"ROWTIME":1578477403591,"ROWKEY":"null","transaction":"PAYMENT","amount":"$125.0"}
{"ROWTIME":1578477598555,"ROWKEY":"null","transaction":"PAYMENT","amount":"$125.0"}

-- Declare the schema
CREATE STREAM rabbit (transaction VARCHAR,
                      amount VARCHAR)
  WITH (KAFKA_TOPIC='rabbit-test-00',
        VALUE_FORMAT='JSON');

-- Reserialise to Avro
CREATE STREAM TRANSACTIONS WITH (VALUE_FORMAT='AVRO', 
                                 KAFKA_TOPIC='reserialised_data') AS
  SELECT *
    FROM rabbit
    EMIT CHANGES;

For more details, see this blog that I've written up.

回答2:

You don't have JSON messages, you have Avro messages coming out of Kafka based on the usages of the AvroConverter.

That letter is not actually a letter, but your terminal showing the UTF8 representation of the first 5 bytes of the binary data. That commonly happens when using regular console consumer, rather than the avro-console-consumer which itself will parse the bytes out of the topic correctly for Avro data

If you want JSON throughout, use the JSONConverter instead

来源：https://stackoverflow.com/questions/59632068/kafka-connect-is-sending-a-malformed-json

标签

apache-kafka

apache-kafka-connect