Common connectors (JDBC, S3, Elasticsearch) in Kafka - Step-by-Step Execution

Process Flow - Common connectors (JDBC, S3, Elasticsearch)

Kafka Source Topic

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Connector Configuration

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Connector Plugin

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JDBC

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Data Sink

Data flows from Kafka through a connector configured to send data to JDBC, S3, or Elasticsearch sinks.

Execution Sample

Kafka

name=jdbc-sink-connector
connector.class=io.confluent.connect.jdbc.JdbcSinkConnector
topics=my_topic
connection.url=jdbc:postgresql://localhost:5432/mydb
insert.mode=insert

This config sets up a JDBC sink connector to write Kafka topic data into a PostgreSQL database.

Process Table

Step	Action	Connector	Input	Output	Result
1	Read message from Kafka topic	All	Kafka message	Message data	Message ready for processing
2	Apply connector config	JDBC	Message data	SQL Insert statement	Prepared SQL for DB
3	Send data to sink	JDBC	SQL Insert statement	Database row	Data stored in DB
4	Read message from Kafka topic	S3	Kafka message	Message data	Message ready for processing
5	Apply connector config	S3	Message data	File object	Data formatted for S3
6	Send data to sink	S3	File object	S3 bucket file	Data stored in S3
7	Read message from Kafka topic	Elasticsearch	Kafka message	Message data	Message ready for processing
8	Apply connector config	Elasticsearch	Message data	JSON document	Data formatted for ES
9	Send data to sink	Elasticsearch	JSON document	ES index document	Data indexed in ES
10	No more messages	All	-	-	Connector idle, waiting for new messages

💡 No more messages in Kafka topic, connectors wait for new data.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	After Step 8	After Step 9	Final
Message	None	Kafka message	Message data	SQL Insert statement	None	Kafka message	File object	None	Kafka message	JSON document	None
Data Sink	Empty	Empty	Empty	Database row	Empty	Empty	S3 bucket file	Empty	Empty	ES index document	Idle

Key Moments - 3 Insights

Why does the message variable reset to None after sending to the sink?

After the connector sends data to the sink (see steps 3, 6, 9), the message is processed and cleared to prepare for the next message, as shown in the execution_table.

How does the connector know which sink to send data to?

The connector.class setting in the configuration (see execution_sample) determines which sink plugin is used, directing data to JDBC, S3, or Elasticsearch accordingly.

Why are there repeated steps for reading messages in the execution_table?

Each connector independently reads messages from Kafka to process them for its sink, so steps repeat for JDBC, S3, and Elasticsearch connectors separately.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after step 5?

A SQL Insert statement

B File object

C JSON document

D Database row

💡 Hint

Check the 'Output' column for step 5 in the execution_table.

At which step does the data get stored in Elasticsearch?

A Step 9

B Step 6

C Step 3

D Step 10

💡 Hint

Look for 'Data indexed in ES' in the 'Result' column of the execution_table.

If the connector.class is changed to S3, which steps would no longer occur?

A Steps 4 and 5

B Steps 7 and 8

C Steps 2 and 3

D Steps 1 and 10

💡 Hint

Refer to the 'Connector' column in the execution_table to see which steps belong to JDBC.

Concept Snapshot

Common Kafka connectors move data from Kafka topics to external systems.
Use connector.class to select sink: JDBC for databases, S3 for storage, Elasticsearch for search.
Connectors read messages, transform data, then write to the sink.
Each connector runs independently but follows the same flow: read, transform, write.
Configure connectors with properties like topics, connection URLs, and modes.

Full Transcript

This visual execution shows how Kafka connectors work to move data from Kafka topics to external systems like JDBC databases, S3 storage, and Elasticsearch indexes. The flow starts with reading messages from Kafka, applying connector-specific configurations, transforming the data into the required format, and finally sending it to the sink. Each connector type (JDBC, S3, Elasticsearch) processes messages independently but follows the same steps. Variables like 'Message' and 'Data Sink' change as data moves through the steps. Key moments clarify why messages reset after sending and how connectors know their sink. The quiz tests understanding of outputs at different steps and connector behavior. This helps beginners see the step-by-step data movement in Kafka connectors.