Sink connectors in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kafka Connect sink connector configuration?

Given the following sink connector configuration snippet, what will be the value of the topics property after parsing?

Kafka

{
  "name": "my-sink-connector",
  "config": {
    "connector.class": "FileStreamSink",
    "tasks.max": "1",
    "topics": "topic1,topic2,topic3",
    "file": "/tmp/output.txt"
  }
}

A ["topic1 topic2 topic3"]

B ["topic1", "topic2", "topic3"]

C null

D "topic1,topic2,topic3"

💡 Hint

The topics property is a string listing topics separated by commas.

The 'topics' property in Kafka Connect sink connector config is a single string with comma-separated topic names. It is not automatically parsed into a list.

🧠 Conceptual

intermediate

Which option best describes the role of a Kafka Sink Connector?

What is the main purpose of a Kafka Sink Connector in Kafka Connect?

A To read data from external systems and write it into Kafka topics.

B To monitor Kafka broker health and performance.

C To read data from Kafka topics and write it into external systems.

D To manage Kafka cluster configurations automatically.

💡 Hint

Sink connectors move data out of Kafka.

Sink connectors consume data from Kafka topics and write it to external systems like databases, files, or other services.

🔧 Debug

advanced

Identify the error in this sink connector configuration snippet

This sink connector configuration is intended to write Kafka topic data to a file. What error will it cause?

Kafka

{
  "name": "file-sink",
  "config": {
    "connector.class": "FileStreamSink",
    "tasks.max": 1,
    "topics": ["my-topic"],
    "file": "/tmp/output.log"
  }
}

A Runtime error because 'tasks.max' must be a string

B SyntaxError due to JSON array in 'topics' property

C No error; configuration is valid

D Configuration error because 'file' path is invalid

💡 Hint

The 'topics' property expects a string, not an array.

The 'topics' property must be a comma-separated string, not a JSON array. Using an array causes a configuration parsing error.

📝 Syntax

advanced

Which option correctly defines a sink connector with exactly 3 tasks?

Select the valid JSON snippet that sets up a sink connector with 3 parallel tasks.

A { "name": "sink-connector", "config": { "connector.class": "JdbcSinkConnector", "tasks.max": "3", "topics": "orders", "connection.url": "jdbc:mysql://localhost:3306/shop" } }

B { "name": "sink-connector", "config": { "connector.class": "JdbcSinkConnector", "tasks.max": 3, "topics": "orders", "connection.url": "jdbc:mysql://localhost:3306/shop" } }

C { "name": "sink-connector", "config": { "connector.class": "JdbcSinkConnector", "tasks.max": "three", "topics": "orders", "connection.url": "jdbc:mysql://localhost:3306/shop" } }

D { "name": "sink-connector", "config": { "connector.class": "JdbcSinkConnector", "tasks.max": "3 tasks", "topics": "orders", "connection.url": "jdbc:mysql://localhost:3306/shop" } }

💡 Hint

The 'tasks.max' property must be a string representing a number.

In Kafka Connect configurations, numeric values like 'tasks.max' must be strings. Option A correctly uses "3" as a string.

🚀 Application

expert

How many tasks will run for this sink connector configuration?

Consider this sink connector config: { "name": "multi-task-sink", "config": { "connector.class": "FileStreamSink", "tasks.max": "5", "topics": "topicA,topicB" } } If the Kafka Connect cluster has only 3 worker nodes available, how many tasks will actually run?

A Only 1 task will run because FileStreamSink supports a single task.

B 5 tasks will run, distributed across the 3 workers.

C 3 tasks will run, limited by the number of available workers.

D No tasks will run due to configuration conflict.

💡 Hint

Some connectors limit the number of tasks regardless of 'tasks.max'.

The FileStreamSink connector supports only a single task regardless of the 'tasks.max' setting. So only 1 task runs.

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