Kafka

The Kafka input component enable consuming messages from Kafka topics with configurable settings such as partition fetch size, offset reset policies, and balancing strategies.

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Config Definition

class Kafka extends Input {
  fixed sourceName = "kafka"
  common: Common.Kafka
  autoCommitEnabled: Boolean = true
  consumerGroupID: String
  autoOffsetReset: AutoOffsetReset = "earliest"
  balancerStrategy: Listing<Strategy> = new Listing<Strategy> {
    "cooperative-sticky"
  }
  maxPartitionFetchBytes: DataSize(validateBuffersSizes) = 1.mib
  fetchMaxBytes: DataSize(validateBuffersSizes) = 50.mib
}

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Common.Kafka Definition

The common attribute of the Kafka input component references the Common.Kafka class, which defines essential configurations for connecting to Kafka brokers and interacting with topics.

Common.Kafka Config

class KafkaAuth {
   saslMechanism: SASLMechanism
   saslUsername: String
   saslPassword: String
}

class Kafka {
   saslAuth: KafkaAuth?
   brokers: Listing<String>
   version: String?
   topics: Listing<String>
}

Common.Kafka Attributes

Attribute	Type	Description	Default Value
saslMechanism	SASLMechanism	SASL mechanism to use (SCRAM-SHA-512 or SCRAM-SHA-256).	null
saslUsername	String	SASL authentication username.	null
saslPassword	String	SASL authentication password.	null
brokers	Listing<String>	List of Kafka broker addresses.	Required
version	String	Kafka protocol version (optional).	null
topics	Listing<String>	List of Kafka topics to subscribe to.	Required

Validations

1. SASL Mechanism Validation

   • If saslAuth is not null and saslMechanism is not set, the following error is thrown:

     'saslMechanism' can not be null
     

2. SASL Credentials Validation

   • If saslAuth is not null, both saslUsername and saslPassword must be provided. Otherwise, the following error is thrown:

   'saslUsername' and 'saslPassword' can not be empty string or null
   

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Kafka Input Attributes

Attribute	Type	Description	Default Value
common	Common.Kafka	Reusable Kafka connection settings (e.g., brokers, SASL).	Required
autoCommitEnabled	Boolean	Enables or disables auto-commit for consumer offsets.	true
consumerGroupID	String	Consumer group ID for managing Kafka consumers and partition ownership.	Required
autoOffsetReset	AutoOffsetReset	Behavior when there is no initial offset or when the offset is invalid (earliest or latest).	"earliest"
balancerStrategy	Listing<Strategy>	Strategy used for partition assignment during rebalancing.	["cooperative-sticky"]
maxPartitionFetchBytes	DataSize	Maximum data fetched per partition per request.	1.mib
fetchMaxBytes	DataSize	Maximum data fetched across all partitions per request.	50.mib

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Validations

Buffer Size Validation

• Ensures fetchMaxBytes is greater than or equal to maxPartitionFetchBytes.
• If the validation fails, an exception is thrown:

  'fetchMaxBytes' should be more than 'maxPartitionFetchBytes'
  

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Pkl Configuration Example

Basic Kafka Input

new Inputs.Kafka {
  common = new Common.Kafka {
    brokers = {
     "broker1:9092"
      "broker2:9092"
     }
    topics = {
     "example-topic"
    }
  }
  consumerGroupID = "example-consumer-group"
}

Kafka Input with SASL Authentication

new Inputs.Kafka {
  common = new Common.Kafka {
    saslEnabled = true
    saslMechanism = "SCRAM-SHA-512"
    saslUsername = "example-user"
    saslPassword = "example-password"
    brokers = {
     "broker1:9092"
      "broker2:9092"
     }
    topics = {
       "secure-topic"
    }
  }
  consumerGroupID = "example-secure-consumer"
}

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Attributes in Detail

Common Kafka Settings (common)

• Defines reusable Kafka connection attributes (e.g., brokers, topics, SASL authentication).

Auto Commit Enabled (autoCommitEnabled)

• If true, offsets are automatically committed to Kafka.
• If false, manual offset commit is required.

Consumer Group ID (consumerGroupID)

• Identifies the group of Kafka consumers that share load and maintain offset tracking.

Offset Reset Behavior (autoOffsetReset)

• earliest: Start consuming from the earliest available message.
• latest: Start consuming from the latest message.

Partition Balancing Strategy (balancerStrategy)

• Default: cooperative-sticky ensures minimal partition movement during rebalancing.
• Custom strategies can be added for advanced partitioning needs.

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Use Cases

1. Basic Kafka Consumption

   • Use the common attribute to specify brokers and topics, along with a consumer group ID for basic use cases.

2. Secure Kafka Consumption

   • Use saslEnabled, saslMechanism, saslUsername, and saslPassword to secure the Kafka connection.

3. Optimized Data Transfer

   • Adjust maxPartitionFetchBytes and fetchMaxBytes to fine-tune data fetching and improve performance.

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Notes

• Ensure Common.Kafka is configured with valid brokers and topics.
• Validate buffer sizes (fetchMaxBytes and maxPartitionFetchBytes) to avoid runtime errors.

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