Status

Current state: Under Discussion

Discussion thread: TODO here

JIRA: TODO here

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Kafka has a feature that allows for the auto-creation of topics. Upon a produce or consume request, when fetching metadata for a topic that does not yet exist, the topic may be created if the broker enables topic auto creation. In the early days of Kafka, this was one of only a few ways to create topics. However, with the addition of AdminClient, this functionality is no longer the recommended way to create topics. 

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However, many cloud users rely on the auto-create functionality. They often use software that they did not write and can not easily change that relies on auto-creation. Thus, moving the auto-create functionality to the producer will still support topic auto-creation, but will do away with some of the negative aspects of the current implementation. Auto-creation can then be configured on a client-by-client basis.

Public Interfaces

The producer will have a few new configurations configuration added. Default values of -1 will use broker defaults or raise an exception.

The goal is to deprecate automatic topic creation on the broker. At some point in the future, it may be useful to set the broker's auto.create.topics.enable default to false. However, for compatibility reasons, doing so is not possible at this time. Likewise, it would make sense to eventually change the default of the consumer's allow.auto.create.topics to false since it has no effect if the broker configuration is false. 

Proposed Changes

The idea is to move the configuration and ability to automatically create topics to client-side on the producer.  Broker auto-topic creation will be deprecated. This includes deprecating the configuration 'auto.create.topics.enable' on the broker and 'allow.auto.create.topics' on the consumer. In the producer, auto-creation of a topic will occur through a specific request rather than through a side effect of requesting metadata.  Unlike the configuration in the consumer, the ability to automatically create topics client-side will be independent of the server-side automatic topic creation controlled by the broker configuration.

If the broker config, 'auto.create.topics.enable' is set to true, a warning will be given that states the config is deprecated.

If server-side auto-creation is enabled with the broker's auto.create.topics.enable, the broker's defaults for partitions and replication factor will be used. When client-side auto-creation is enabledAuto creation will try to use client-side configurations if set. However, if none exist, as represented by -1, broker-side defaults can will be used if the broker supports KIP 464. AutoClient-side auto-creation is not supported for older brokers if no client configurations are given. 

Compatibility, Deprecation, and Migration Plan

This KIP argues for deprecation of the broker config auto.create.topics.enable. However, the default will remain true, so there will be no compatibility issues with current usage of the config and its functionality.

In order to automatically create topics with the producer, the producer's .auto.create.topics.enable config topics config must be set to true. 'client-side.'  If the broker does not support KIP 464, auto.create.num.partitions and auto.create.replication.factor must be specified. 

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This KIP does not plan on changing the broker default. However, it is useful to understand compatibility issues if this were to happen. 

• • By default, 'allow-server-side' auto-creation is used. The broker's 'auto.create.topics.enable' must be configured as true.
    • Although the broker config and server-side auto-creation is deprecated, this is the default to ensure compatibility.
    • If the broker config is set to false, the topic will not be created automatically.
  • Systems that rely on auto-creation would be encouraged to set the producer config producer.auto.create.topics
.enable
• • to 'client-side.'
    • This will effectively override the deprecated broker config, so even if it is configured to true,
but could also rely on the deprecated broker config
• • • the server will not auto-create topics.
    • Systems with older broker versions
would need to set auto.create.num.partitions and auto.create.replication.factor upon allowing producer auto-creation.
• • • that do not support KIP-464 would not be compatible with this option.
  • Systems that want to turn off auto-creation completely should set the producer config to false. This will override the broker config for this producer.
    • This will fulfill the same role as 'allow.
Setting both the broker and producer
• • • auto.create.topics
.enable to true is not advised. 
• • • ' on the consumer, but for the producer.
  • Systems that utilize auto-creation on the consumer will no longer be able to do so with only the producer config enabled.
    • Enabling the broker config or making further changes to the code is required
.After changing the broker default to false, there are a few changes/compatibility issues
• • • .

Rejected Alternatives

• Enabling true by default on the producer config:
Setting both the broker config and the producer config to true could result in both attempting to create new topics and result in excess requests to the broker.
• • Topic auto-creation is a feature that is not supported as it once was, so defaulting to false supports this trend towards using admin client to create topics. Auto-creation does not work on older brokers without configuration client-side anyway, so it might be more clear that configuration must be done in order to keep using this feature. 
• Add configurations producer-side for replication factor, partitions of new topics
  • The idea is to keep this simple; configuring these values is not simple and could add to more issues for users.