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Console Producer and Consumer for Avro messages

Question:

What is the simplest way to write and read messages encoded in Avro to and from Kafka?

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Example use case:

So you are excited to get started with Kafka and you would like to produce and consume some messages in Avro format. In this tutorial we'll show you how to produce and consume messages from the command line with no code!

Code example:

Basic Kafka

Try it

1
Initialize the project

To get started, make a new directory anywhere you’d like for this project:

mkdir console-consumer-producer-avro && cd console-consumer-producer-avro

2
Get Confluent Platform

Next, create the following docker-compose.yml file to obtain Confluent Platform.

---
version: '2'

services:
  zookeeper:
    image: confluentinc/cp-zookeeper:6.1.0
    hostname: zookeeper
    container_name: zookeeper
    ports:
      - "2181:2181"
    environment:
      ZOOKEEPER_CLIENT_PORT: 2181
      ZOOKEEPER_TICK_TIME: 2000

  broker:
    image: confluentinc/cp-kafka:6.1.0
    hostname: broker
    container_name: broker
    depends_on:
      - zookeeper
    ports:
      - "29092:29092"
    environment:
      KAFKA_BROKER_ID: 1
      KAFKA_ZOOKEEPER_CONNECT: 'zookeeper:2181'
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,PLAINTEXT_HOST:PLAINTEXT
      KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://broker:9092,PLAINTEXT_HOST://localhost:29092
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0

  schema-registry:
    image: confluentinc/cp-schema-registry:6.1.0
    hostname: schema-registry
    container_name: schema-registry
    depends_on:
      - zookeeper
      - broker
    ports:
      - "8081:8081"
    environment:
      SCHEMA_REGISTRY_HOST_NAME: schema-registry
      SCHEMA_REGISTRY_KAFKASTORE_BOOTSTRAP_SERVERS: 'broker:9092'
    volumes:
      - ./schema:/opt/app/schema/

Now launch Confluent Platform by running:

docker-compose up -d

3
Create a topic

Your first step is to create a topic to produce to and consume from. Use the following command to create the topic:

docker-compose exec broker kafka-topics --create --topic example-topic-avro --bootstrap-server broker:9092 --replication-factor 1 --partitions 1

4
Create a schema

Next let’s create the schema to use when formatting the messages to produce to the topic created in previous step.

Note that when you executed the docker-compose up command, it created a directory named schema on your local machine.

From the same terminal you used to create the topic, create the following order_detail.avsc file inside the schema directory

{
  "type": "record",
  "namespace": "io.confluent.tutorial.pojo.avro",
  "name": "OrderDetail",
  "fields": [
    {
      "name": "number",
      "type": "long",
      "doc": "The order number."
    },
    {
      "name": "date",
      "type": "long",
      "logicalType": "date",
      "doc": "The date the order was submitted."
    },
    {
      "name": "shipping_address",
      "type": "string",
      "doc": "The shipping address."
    },
    {
      "name": "subtotal",
      "type": "double",
      "doc": "The amount without shipping cost and tax."
    },
    {
      "name": "shipping_cost",
      "type": "double",
      "doc": "The shipping cost."
    },
    {
      "name": "tax",
      "type": "double",
      "doc": "The applicable tax."
    },
    {
      "name": "grand_total",
      "type": "double",
      "doc": "The order grand total ."
    }
  ]
}

5
Start an Avro console consumer

Next let’s open up an Avro console consumer to read records sent to the topic you created in previous step.

From the same terminal you used to create the topic and schema above, run the following command to open a terminal on the broker container:

docker-compose exec schema-registry bash

From within the terminal on the schema-registry container, run this command to start an Avro console consumer:

kafka-avro-console-consumer --topic example-topic-avro --bootstrap-server broker:9092

The consumer will start up and block waiting for records, you won’t see any output until after the next step.

6
Produce your first Avro records

To produce your first Avro record into Kafka, open another terminal window and run the following command to open a second shell on the broker container:

docker-compose exec schema-registry bash

From inside the second terminal on the schema-registry container, run the following command to start a console producer with the schema you created previously:

kafka-avro-console-producer --topic example-topic-avro --bootstrap-server broker:9092 --property value.schema="$(< /opt/app/schema/order_detail.avsc)"

The producer will start and wait for you to enter input. Each line represents one Avro record and to send it you’ll hit the enter key.

Try copying and pasting one line at a time, hit enter and go back to the Avro console consumer window and look for the output.

{"number": 2343434, "date": 1596490462, "shipping_address": "456 Everett St, Palo Alto, 94301 CA, USA", "subtotal": 99.0, "shipping_cost": 0.0, "tax": 8.91, "grand_total": 107.91}
{"number": 2343435, "date": 1596491687, "shipping_address": "518 Castro St, Mountain View, 94305 CA, USA", "subtotal": 25.0, "shipping_cost": 0.0, "tax": 2.91, "grand_total": 27.91}

Once you’ve sent all the records you should see the same output in your Avro console consumer window. After you’ve confirmed receiving all records go ahead and close the consumer by entering CTRL+C.

7
Read all records

In the first consumer example, you observed all incoming records because the consumer was already running, waiting for incoming records.

But what if the records were produced before you started your consumer? In that case you wouldn’t see the records as the console consumer by default only reads incoming records arriving after it has started up.

But what about reading previously sent records? In that case, you’ll add one property --from-beginning to the start command for the console consumer.

To demonstrate reading from the beginning, close the current console consumer in the consumer terminal by typing Ctrl+C

Now go back to your producer console and send the following records:

{"number": 2343436, "date": 1596491687, "shipping_address": "89 Addison St, Palo Alto, 94302 CA, USA", "subtotal": 10.0, "shipping_cost": 0.0, "tax": 1, "grand_total": 11.0}
{"number": 2343437, "date": 1596490492, "shipping_address": "456 Charles St, Beverly Hills, 90209 CA, USA", "subtotal": 450.0, "shipping_cost": 10.0, "tax": 28.91, "grand_total": 488.91}
{"number": 2343438, "date": 1596490692, "shipping_address": "456 Preston St, Brooklyn, 11212 NY, USA", "subtotal": 34.0, "shipping_cost": 2.0, "tax": 3, "grand_total": 39.00}

8
Start a new consumer to read all records

Next let’s open up a console consumer again, but this time you will consume everything including what the producer sent in the previous step.

Run this command in the container shell you created for your first consumer and note the additional property --from-beginning:

kafka-avro-console-consumer --topic example-topic-avro --bootstrap-server broker:9092  --from-beginning

After the consumer starts you should see the following output in a few seconds:

{"number":2343434,"date":1596490462,"shipping_address":"456 Everett St, Palo Alto, 94301 CA, USA","subtotal":99.0,"shipping_cost":0.0,"tax":8.91,"grand_total":107.91}
{"number":2343435,"date":1596491687,"shipping_address":"518 Castro St, Mountain View, 94305 CA, USA","subtotal":25.0,"shipping_cost":0.0,"tax":2.91,"grand_total":27.91}
{"number":2343436,"date":1596491687,"shipping_address":"89 Addison St, Palo Alto, 94302 CA, USA","subtotal":10.0,"shipping_cost":0.0,"tax":1.0,"grand_total":11.0}
{"number":2343437,"date":1596490492,"shipping_address":"456 Charles St, Beverly Hills, 90209 CA, USA","subtotal":450.0,"shipping_cost":10.0,"tax":28.91,"grand_total":488.91}
{"number":2343438,"date":1596490692,"shipping_address":"456 Preston St, Brooklyn, 11212 NY, USA","subtotal":34.0,"shipping_cost":2.0,"tax":3.0,"grand_total":39.0}
{"number":2343439,"date":1596501510,"shipping_address":"1600 Pennsylvania Avenue NW, Washington, DC 20500, USA","subtotal":1000.0,"shipping_cost":20.0,"tax":0.0,"grand_total":1020.0}
{"number":2343440,"date":1596501510,"shipping_address":"55 Music Concourse Dr, San Francisco, CA 94118, USA","subtotal":345.0,"shipping_cost":10.0,"tax":10.0,"grand_total":365.0}

One word of caution with using the --from-beginning flag. As the name implies this setting forces the consumer retrieve every record currently on the topic. So it’s best to use when testing and learning and not on a production topic.

Again, once you’ve received all records, close this console consumer by entering a CTRL+C.

9
Produce records with full key-value pairs

Kafka works with key-value pairs, but so far you’ve only sent records with values only. Well to be fair you’ve sent key-value pairs, but the keys are null. Sometimes you’ll need to send a valid key in addition to the value from the command line.

To enable sending full key-value pairs from the command line you add two properties to your console producer, parse.key and key.separator

Let’s try to send some full key-value records now. If your previous console producer is still running close it with a CTRL+C and run the following command to start a new console producer:

kafka-avro-console-producer --topic example-topic-avro --bootstrap-server broker:9092 \
 --property key.schema='{"type":"string"}' \
 --property value.schema="$(< /opt/app/schema/order_detail.avsc)" \
 --property parse.key=true \
 --property key.separator=":"

Then enter these records either one at time or copy-paste all of them into the terminal and hit enter:

"122345":{"number": 2343439, "date": 1596501510, "shipping_address": "1600 Pennsylvania Avenue NW, Washington, DC 20500, USA", "subtotal": 1000.0, "shipping_cost": 20.0, "tax": 0.00, "grand_total": 1020.00}
"256743":{"number": 2343440, "date": 1596501510, "shipping_address": "55 Music Concourse Dr, San Francisco, CA 94118, USA", "subtotal": 345.00, "shipping_cost": 10.00, "tax": 10.00, "grand_total": 365.00}

10
Start a consumer to show full key-value pairs

Now that we’ve produced full key-value pairs from the command line, you’ll want to consume full key-value pairs from the command line as well.

If your console consumer from the previous step is still open, shut it down with a CTRL+C. Then run the following command to re-open the console consumer but now it will print the full key-value pair. Note the added properties of print.key and key.separator. You should also take note that there’s a different key separator used here, you don’t have to use the same one between console producers and consumers.

kafka-avro-console-consumer --topic  example-topic-avro --bootstrap-server broker:9092 \
 --from-beginning \
 --property print.key=true \
 --property key.separator="-"

After the consumer starts you should see the following output in a few seconds:

null-{"number":2343434,"date":1596490462,"shipping_address":"456 Everett St, Palo Alto, 94301 CA, USA","subtotal":99.0,"shipping_cost":0.0,"tax":8.91,"grand_total":107.91}
null-{"number":2343435,"date":1596491687,"shipping_address":"518 Castro St, Mountain View, 94305 CA, USA","subtotal":25.0,"shipping_cost":0.0,"tax":2.91,"grand_total":27.91}
null-{"number":2343436,"date":1596491687,"shipping_address":"89 Addison St, Palo Alto, 94302 CA, USA","subtotal":10.0,"shipping_cost":0.0,"tax":1.0,"grand_total":11.0}
null-{"number":2343437,"date":1596490492,"shipping_address":"456 Charles St, Beverly Hills, 90209 CA, USA","subtotal":450.0,"shipping_cost":10.0,"tax":28.91,"grand_total":488.91}
null-{"number":2343438,"date":1596490692,"shipping_address":"456 Preston St, Brooklyn, 11212 NY, USA","subtotal":34.0,"shipping_cost":2.0,"tax":3.0,"grand_total":39.0}
"122345"-{"number":2343439,"date":1596501510,"shipping_address":"1600 Pennsylvania Avenue NW, Washington, DC 20500, USA","subtotal":1000.0,"shipping_cost":20.0,"tax":0.0,"grand_total":1020.0}
"256743"-{"number":2343440,"date":1596501510,"shipping_address":"55 Music Concourse Dr, San Francisco, CA 94118, USA","subtotal":345.0,"shipping_cost":10.0,"tax":10.0,"grand_total":365.0}

Since we kept the --from-beginning property, you’ll see all the records sent to the topic. You’ll notice the results before you sent keys are formatted as null-<value>.

11
Clean Up

You’re all done now!

Go back to your open windows and stop any console producers and consumers with a CTRL+C then close the container shells with a CTRL+D command.

Then you can shut down the stack by running:

docker-compose down -v

Deploy on Confluent Cloud

1
Run your app to Confluent Cloud

Instead of running a local Kafka cluster, you may use Confluent Cloud, a fully-managed Apache Kafka service.

First, create your Kafka cluster in Confluent Cloud. Use the promo code CC100KTS to receive an additional $100 free usage (details).

Next, from the Confluent Cloud UI, click on Tools & client config to get the cluster-specific configurations, e.g. Kafka cluster bootstrap servers and credentials, Confluent Cloud Schema Registry and credentials, etc., and set the appropriate parameters in your client application.

Now you’re all set to run your streaming application locally, backed by a Kafka cluster fully managed by Confluent Cloud.