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• Client Behaviors

  • Clients won’t attempt to resolve the bootstrap addresses upon initialization.

  • Clients won’t exit fatally if DNS resolution fails.

  • KafkaConsumer: Users must poll to retry the lookup if it fails.

  • KafkaAdminClient: Users will need to resend the request if failing.

  • KafkaProducer: The sender loop should already be polling continuously.

  Exception Handling

  • Failed DNS resolution will result in NetworkException

Case Study

To help illustrate the proposed changes, we provide some examples of how clients might behave in different scenarios.

KafkaConsumer

Case 1: Unable to connect to the bootstrap (For example: misconfiguration)

Suppose the user instantiates a KafkaConsumer with an invalid bootstrap config. When the user invokes assign() and starts poll(), the poll() method will continue to return empty ConsumerRecords and log a warning message.

The user can continue to retry for the configured duration. After the bootstrap timeout expires, the client will throw a BootstrapConnectionException.

Case 2: Transient Network Issue (For example: transient DNS failure)

Now, suppose the user instantiates a KafkaConsumer with a valid bootstrap config, but there is a transient network issue, such as slow DNS resolution.

When the user starts poll(), the poll() method will return an empty ConsumerRecord and log a warning message.

The user can continue to retry, and the network issue will be successfully resolved after some time. The KafkaConsumer will then continue to function normally.

KafkaProducer

Case 1: Unable to connect to the bootstrap (For example: misconfiguration)

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Suppose the user instantiates a KafkaProducer with an invalid bootstrap config.

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As the produce is instantiated, the sender thread starts running

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.  A warning message is logged everytime the NetworkClient tries to poll().

If the user tries to produce messages

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, the producer callback may be completed with a TimeoutException until the bootstrap timeout runs out.

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Eventually, a BootstrapConnectionException will be thrown.

Case 2: Transient Network Issue (For example: transient DNS failure)

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Now, suppose the user instantiates a KafkaProducer with a valid bootstrap config, but there is a transient network issue. As the sender thread starts running, a

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warning message is logged upon trying to bootstrap the client.

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If the network issue is resolved before the user tries to produce a message

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, only warning messages will be logged.

If the user tries to produce a message before the issue is resolved

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, the sender callback will be completed with a TimeoutException if the network issue persists.

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The send

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will be completed normally if the network issue is resolved before exhausting the max.block.ms.

AdminClient

Case 1: Unable to connect to the bootstrap (For example: misconfiguration)

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