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

Motivation

AdminClient::describeConfigs

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api takes a Collection

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of ConfigResource objects as an argument to get all the configurations of the entities specified. Here is the api signature:

DescribeConfigsResult describeConfigs(Collection<ConfigResource> resources, DescribeConfigsOptions options);

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The ConfigResource

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class is made up of two fields, name of the entity (“topic-1”, “broker-1” etc) and type of the entity (BROKER, TOPIC etc) of the entity. DescribeConfigsOptions allows use to specify whether to fetch config synonyms and their documentation. The api response contains all configurations for the specified entities.

This admin api in turn

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calls DescribeConfigsRequest

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kafka api to get the configuration for specified entities. DescribeConfigsRequest api takes a collection of DescribeConfigsResource objects to specify entities whose configuration needs to be fetched. So to make this Kafka API call, AdminClient::describeConfigs converts ConfigResource

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 collection passed to it to a DescribeConfigsResource

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 collection. In addition to name and type of entity whose configuration to get,

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Kafka DescribeConfigsResource

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structure also lets users

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provide ConfigurationKeys, a list of String, which allows users to specify only the configurations that they are interested in. As this information isn’t present in the ConfigResource class, it is set to null

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 when DescribeConfigsResource object is created from it. Here is the code doing this (

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KafkaAdminClient.java

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)

.map(config ->
    new DescribeConfigsRequestData.DescribeConfigsResource()
        .setResourceName(config.name())
        .setResourceType(config.type().id())
        .setConfigurationKeys(null))

This means that all configurations of all the entities specified are returned by Kafka. Then the user of

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the AdminClient::describeConfigs iterates over the returned list and filters out the configuration keys that they are interested in.

This results in boilerplate code for all users

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of AdminClient::describeConfigs api, in addition to  being wasteful use of resource. It becomes painful for large clusters where to fetch one configuration of all topics, we need to fetch all configuration of all topics, which can result in huge response. Alternatively, request can be batched, but then one api request gets broken down in tens if not hundred of api request depending on batch size, complicating error handling and retries.

This is also a usability issue when running kafka-configs

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 command which returns all configurations and then user need to either scan or filter for property that they are interested in.

We need to a way to

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specify ConfigurationKeys

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 parameter that DescribeConfigsResource takes

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to bring

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AdminClient::describeConfigs api to parity with DescribeConfigsResource

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 and allow AdminClient’s users to specify configuration keys that they are interested in.

In addition we need to add same option to kafka-configs

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 command line utility so that users of the tool don’t need to fetch all configurations when they are interested in only a few of them.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

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