Sink connectors in Kafka - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a sink connector in Kafka Connect?

A sink connector is a component in Kafka Connect that reads data from Kafka topics and writes it to an external system like a database, file system, or search index.

beginner

Name two common external systems where sink connectors send data.

Common external systems include relational databases (like MySQL, PostgreSQL) and search engines (like Elasticsearch).

beginner

How does a sink connector know which Kafka topic to read from?

The sink connector configuration specifies the Kafka topic(s) it should read data from using the 'topics' property.

intermediate

What is the role of the 'tasks.max' setting in sink connectors?

'tasks.max' defines the maximum number of tasks (parallel workers) the sink connector can use to write data to the external system, improving throughput.

intermediate

Why is it important to handle data format compatibility in sink connectors?

Sink connectors must convert Kafka record formats (like Avro, JSON) into the format expected by the external system to avoid errors and data loss.

What does a Kafka sink connector do?

A Reads data from Kafka and writes it to an external system

B Reads data from an external system and writes it to Kafka

C Manages Kafka cluster configuration

D Monitors Kafka topic partitions

A sink connector reads data from Kafka topics and writes it to external systems.

Which configuration property specifies the Kafka topics a sink connector reads from?

A connect.topics

B source.topics

C topics

D sink.topics

The 'topics' property lists the Kafka topics the sink connector consumes.

What does the 'tasks.max' setting control in a sink connector?

A Maximum retries on failure

B Maximum Kafka topic partitions

C Maximum message size

D Maximum number of parallel tasks for writing data

'tasks.max' controls how many parallel tasks the connector can run to improve throughput.

Which of these is NOT a typical sink connector destination?

A Relational databases

B Kafka topics

C File systems

D Search indexes

Kafka topics are source for sink connectors, not a destination.

Why must sink connectors handle data format conversion?

A To match the external system's expected data format

B To encrypt data before sending

C To compress data for faster transfer

D To change Kafka topic names

Data format conversion ensures compatibility with the external system receiving the data.

Explain what a sink connector is and how it works in Kafka Connect.

Think about how data flows from Kafka to other systems.

Describe why data format compatibility is important for sink connectors and how it affects data transfer.

Consider what happens if the external system expects a different format.

Practice

1.

What is the main purpose of a Kafka sink connector?

easy

A. To create new Kafka topics dynamically

B. To move data from external systems into Kafka topics

C. To monitor Kafka cluster health

D. To move data from Kafka topics to external systems automatically

Solution

1. Step 1: Understand the role of sink connectors

   Sink connectors are designed to export data from Kafka topics to other systems.

2. Step 2: Differentiate from source connectors

   Source connectors import data into Kafka, while sink connectors export data out.

3. Final Answer:

   To move data from Kafka topics to external systems automatically -> Option D

4. Quick Check:

   Sink connector = export data from Kafka [OK]

Hint: Sink connectors export data out of Kafka topics [OK]

Common Mistakes:

• Confusing sink with source connectors
• Thinking sink connectors create topics
• Assuming sink connectors monitor Kafka health

2.

Which of the following is a correct JSON field to specify the Kafka topic for a sink connector configuration?

{
  "name": "my-sink-connector",
  "config": {
    "connector.class": "io.confluent.connect.jdbc.JdbcSinkConnector",
    "topics": "my_topic",
    "connection.url": "jdbc:mysql://localhost:3306/mydb"
  }
}

easy

A. "topics"

B. "topic"

C. "topic_name"

D. "source.topics"

Solution

1. Step 1: Check the standard Kafka Connect config field

   The field to specify Kafka topics in sink connector config is "topics" (plural).

2. Step 2: Verify the example JSON

   The example uses "topics": "my_topic", which is correct syntax.

3. Final Answer:

   "topics" -> Option A

4. Quick Check:

   Kafka sink config uses "topics" field [OK]

Hint: Use "topics" (plural) to list Kafka topics in config [OK]

Common Mistakes:

• Using "topic" (singular) instead of "topics"
• Using non-standard fields like "topic_name"
• Confusing source connector fields with sink

3.

Given this sink connector config snippet, what will be the destination system?

{
  "name": "file-sink-connector",
  "config": {
    "connector.class": "FileStreamSink",
    "topics": "logs",
    "file": "/tmp/output.log"
  }
}

medium

A. A Kafka topic named 'logs'

B. A file located at /tmp/output.log

C. A database table named 'logs'

D. A remote HTTP endpoint

Solution

1. Step 1: Identify the connector class

   The connector class is "FileStreamSink", which writes data to a file.

2. Step 2: Check the "file" config field

   The "file" field specifies the destination file path "/tmp/output.log".

3. Final Answer:

   A file located at /tmp/output.log -> Option B

4. Quick Check:

   FileStreamSink writes to file path [OK]

Hint: FileStreamSink writes Kafka data to a file path [OK]

Common Mistakes:

• Assuming data goes back to Kafka topic
• Confusing sink with source connectors
• Thinking it writes to a database or HTTP

4.

Identify the error in this sink connector config JSON:

{
  "name": "jdbc-sink",
  "config": {
    "connector.class": "io.confluent.connect.jdbc.JdbcSinkConnector",
    "topic": "orders",
    "connection.url": "jdbc:postgresql://localhost:5432/shop"
  }
}

medium

A. Invalid JDBC URL format

B. Connector class name is incorrect

C. Missing 'topics' field; uses 'topic' instead

D. Missing 'name' field

Solution

1. Step 1: Check the topic field name

   The config uses "topic" (singular), but Kafka sink connectors require "topics" (plural).

2. Step 2: Verify other fields

   The JDBC URL and connector class are correctly formatted, and "name" is present.

3. Final Answer:

   Missing 'topics' field; uses 'topic' instead -> Option C

4. Quick Check:

   Use "topics" not "topic" in sink config [OK]

Hint: Use plural "topics" field in sink connector config [OK]

Common Mistakes:

• Using singular "topic" instead of "topics"
• Assuming JDBC URL is wrong without checking
• Thinking connector class name is invalid

5.

You want to export data from multiple Kafka topics to a single database table using a JDBC sink connector. Which configuration approach is correct?

{
  "name": "multi-topic-jdbc-sink",
  "config": {
    "connector.class": "io.confluent.connect.jdbc.JdbcSinkConnector",
    "topics": "topic1,topic2,topic3",
    "connection.url": "jdbc:mysql://localhost:3306/mydb",
    "table.name.format": "combined_table"
  }
}

hard

A. This config exports all topics to one table named 'combined_table'

B. Each topic will create a separate table ignoring 'table.name.format'

C. The connector will fail because multiple topics are not allowed

D. Data will be merged but only from 'topic1'

Solution

1. Step 1: Understand 'topics' field with multiple topics

   The "topics" field lists multiple topics separated by commas, which is valid.

2. Step 2: Check 'table.name.format' usage

   Setting "table.name.format" to a fixed table name causes all data to go into that single table.

3. Step 3: Confirm connector behavior

   The JDBC sink connector supports writing multiple topics to one table if configured this way.

4. Final Answer:

   This config exports all topics to one table named 'combined_table' -> Option A

5. Quick Check:

   Multiple topics + fixed table name = single table export [OK]

Hint: Use comma-separated topics and fixed table name for single table export [OK]

Common Mistakes:

• Assuming multiple topics create separate tables automatically
• Thinking multiple topics are not allowed in sink config
• Ignoring 'table.name.format' effect