1
Initialize the project
To get started, make a new directory anywhere you’d like for this project:
mkdir connect-add-key-to-source && cd connect-add-key-to-source
2
Prepare the source data
Create a file cities.sql with commands to pre-populate the database table with city information:
DROP TABLE IF EXISTS cities;
CREATE TABLE cities (city_id INTEGER PRIMARY KEY NOT NULL, name VARCHAR(255), state VARCHAR(255));
INSERT INTO cities (city_id, name, state) VALUES (1, 'Raleigh', 'NC');
INSERT INTO cities (city_id, name, state) VALUES (2, 'Mountain View', 'CA');
INSERT INTO cities (city_id, name, state) VALUES (3, 'Knoxville', 'TN');
INSERT INTO cities (city_id, name, state) VALUES (4, 'Houston', 'TX');
INSERT INTO cities (city_id, name, state) VALUES (5, 'Olympia', 'WA');
INSERT INTO cities (city_id, name, state) VALUES (6, 'Bismarck', 'ND');
Create a Dockerfile called Dockerfile-connect that builds a custom container for Kafka Connect bundled with the free and open source JDBC connector, installed from Confluent Hub.
FROM confluentinc/cp-kafka-connect-base:6.2.1
ENV CONNECT_PLUGIN_PATH="/usr/share/java,/usr/share/confluent-hub-components"
RUN confluent-hub install --no-prompt confluentinc/kafka-connect-jdbc:10.0.2
Next, create the following docker-compose.yml file to obtain Confluent Platform. Make sure that you create this file in the same place as the cities.sql file that you created above.
---
version: '2'
services:
zookeeper:
image: confluentinc/cp-zookeeper:6.2.1
hostname: zookeeper
container_name: zookeeper
ports:
- "2181:2181"
environment:
ZOOKEEPER_CLIENT_PORT: 2181
ZOOKEEPER_TICK_TIME: 2000
broker:
image: confluentinc/cp-kafka:6.2.1
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:6.2.1
hostname: schema-registry
container_name: schema-registry
depends_on:
- broker
ports:
- "8081:8081"
environment:
SCHEMA_REGISTRY_HOST_NAME: schema-registry
SCHEMA_REGISTRY_KAFKASTORE_BOOTSTRAP_SERVERS: 'broker:9092'
connect:
image: localimage/kafka-connect-jdbc:latest
build:
context: .
dockerfile: Dockerfile-connect
container_name: connect
depends_on:
- broker
- schema-registry
ports:
- 8083:8083
environment:
CONNECT_BOOTSTRAP_SERVERS: "broker:9092"
CONNECT_REST_ADVERTISED_HOST_NAME: "connect"
CONNECT_REST_PORT: 8083
CONNECT_GROUP_ID: kafka-connect
CONNECT_CONFIG_STORAGE_TOPIC: _kafka-connect-configs
CONNECT_OFFSET_STORAGE_TOPIC: _kafka-connect-offsets
CONNECT_STATUS_STORAGE_TOPIC: _kafka-connect-status
CONNECT_KEY_CONVERTER: io.confluent.connect.avro.AvroConverter
CONNECT_KEY_CONVERTER_SCHEMA_REGISTRY_URL: 'http://schema-registry:8081'
CONNECT_VALUE_CONVERTER: io.confluent.connect.avro.AvroConverter
CONNECT_VALUE_CONVERTER_SCHEMA_REGISTRY_URL: 'http://schema-registry:8081'
CONNECT_LOG4J_ROOT_LOGLEVEL: "INFO"
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"
kafkacat:
image: edenhill/kafkacat:1.5.0
container_name: kafkacat
links:
- broker
entrypoint:
- /bin/sh
- -c
- |
apk add jq;
while [ 1 -eq 1 ];do sleep 60;done
postgres:
# *-----------------------------*
# To connect to the DB:
# docker exec -it postgres bash -c 'psql -U $POSTGRES_USER $POSTGRES_DB'
# *-----------------------------*
image: postgres:11
container_name: postgres
environment:
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=postgres
volumes:
- ./cities.sql:/docker-entrypoint-initdb.d/cities.sql
Now launch Confluent Platform by running the following command. Note the --build argument which automatically builds the Docker image for Kafka Connect and the bundled kafka-connect-jdbc connector.
docker-compose up -d --build
4
Check the source data
Check the data in the source database. Observe the city_id primary key:
echo 'SELECT * FROM cities;' | docker exec -i postgres bash -c 'psql -U $POSTGRES_USER $POSTGRES_DB'
city_id | name | state
---------+---------------+-------
1 | Raleigh | NC
2 | Mountain View | CA
3 | Knoxville | TN
4 | Houston | TX
5 | Olympia | WA
6 | Bismarck | ND
(6 rows)
5
Create the connector
Create the JDBC source connector. Note the transforms stanza which is responsible for setting the key to the value of the city_id field.
curl -i -X PUT http://localhost:8083/connectors/jdbc_source_postgres_01/config \
-H "Content-Type: application/json" \
-d '{
"connector.class": "io.confluent.connect.jdbc.JdbcSourceConnector",
"connection.url": "jdbc:postgresql://postgres:5432/postgres",
"connection.user": "postgres",
"connection.password": "postgres",
"mode":"incrementing",
"incrementing.column.name":"city_id",
"topic.prefix":"postgres_",
"transforms":"copyFieldToKey,extractKeyFromStruct",
"transforms.copyFieldToKey.type":"org.apache.kafka.connect.transforms.ValueToKey",
"transforms.copyFieldToKey.fields":"city_id",
"transforms.extractKeyFromStruct.type":"org.apache.kafka.connect.transforms.ExtractField$Key",
"transforms.extractKeyFromStruct.field":"city_id"
}'
If you run this before Kafka Connect has finished starting up you’ll get the error curl: (52) Empty reply from server - in which case, rerun the above command.
Check that the connector is running:
curl -s http://localhost:8083/connectors/jdbc_source_postgres_01/status
You should see that the state is RUNNING for both connector and tasks elements
{"name":"jdbc_source_postgres_01","connector":{"state":"RUNNING","worker_id":"connect:8083"},"tasks":[{"id":0,"state":"RUNNING","worker_id":"connect:8083"}],"type":"source"}
If you get the message {"error_code":404,"message":"No status found for connector jdbc_source_postgres_01"} then check that the step above in which you created the connector actually succeeded.
6
Consume events from the output topic
With the connector running let’s now inspect the data on the Kafka topic. Here we’ll use kafkacat because of its rich capabilities for inspecting and displaying details of Kafka messages:
docker exec -i kafkacat kafkacat -b broker:9092 -t postgres_cities \
-C -s avro -r http://schema-registry:8081 -e \
-f 'Key (%K bytes):\t%k\nPayload (%S bytes):\t%s\n--\n'
Key (6 bytes): 1
Payload (19 bytes): {"city_id": 1, "name": {"string": "Raleigh"}, "state": {"string": "NC"}}
--
Key (6 bytes): 2
Payload (25 bytes): {"city_id": 2, "name": {"string": "Mountain View"}, "state": {"string": "CA"}}
--
Key (6 bytes): 3
Payload (21 bytes): {"city_id": 3, "name": {"string": "Knoxville"}, "state": {"string": "TN"}}
--
Key (6 bytes): 4
Payload (19 bytes): {"city_id": 4, "name": {"string": "Houston"}, "state": {"string": "TX"}}
--
Key (6 bytes): 5
Payload (19 bytes): {"city_id": 5, "name": {"string": "Olympia"}, "state": {"string": "WA"}}
--
Key (6 bytes): 6
Payload (20 bytes): {"city_id": 6, "name": {"string": "Bismarck"}, "state": {"string": "ND"}}
--
7
Clean up
Shut down the stack by running:
docker-compose down
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