[jira] [Updated] (KAFKA-13336) Migrate StreamsBuilder/Topology class to interfaces and move Topology parameter from KafkaStreams constructor to #start

["A. Sophie Blee-Goldman (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-13336?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

A. Sophie Blee-Goldman updated KAFKA-13336:
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    Summary: Migrate StreamsBuilder/Topology class to interfaces and move Topology parameter from KafkaStreams constructor to #start  (was: Migrate StreamsBuilder class to interface with factory method on KafkaStreams)

> Migrate StreamsBuilder/Topology class to interfaces and move Topology parameter from KafkaStreams constructor to #start
> -----------------------------------------------------------------------------------------------------------------------
>
>                 Key: KAFKA-13336
>                 URL: https://issues.apache.org/jira/browse/KAFKA-13336
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: A. Sophie Blee-Goldman
>            Priority: Major
>              Labels: needs-kip
>
> In order to refactor and improve the streams physical plan generation, we'll need to clean up the DSL builder API a bit and in particular enforce the configs be passed in from the beginning, rather than only when calling #build. We can also use this opportunity to improve the disconnect between the builder, the resulting Topology, and the Kafka Streams application that ultimately runs this topology – at the moment these are all completely uncoupled on the surface, so it's easy to think that a StreamsBuilder can be reused to build multiple Topology objects, or that a Topology object could be passed in to different KafkaStreams. However there is internal state that is shared and modified during StreamsBuilder#build and in the KafkaStreams constructor, and they are actually very coupled under the hood meaning there must be a 1:1:1 ratio of builder to topology to KafkaStreams. So we need a new API that
>  # Forces users to pass in the configs (Properties) when constructing the builder
>  # Clarifies the relationship of the builder object to the topology, and to the app itself
> I think a good API for this might look something like this:
>  # Move the StreamsBuilder class to an internal one (technically we would need to keep it where it is for now until a full deprecation cycle)
>  # Introduce a TopologyBuilder interface to replace the functionality of the current StreamsBuilder class, and have StreamsBuilder implement this. All the current methods on StreamsBuilder will be moved to the TopologyBuilder interfaces
>  # Move the Topology parameter out of the KafkaStreams constructor, and into the KafkaStreams#start method, so you can construct a KafkaStreams object before the Topology
>  # Add a factory method on KafkaStreams for users to get instances of the TopologyBuilder, and have this accept a Properties. For example
> {code:java}
> class KafkaStreams {
>     public void newTopologyBuilder(final Properties props) {
>         // convert to StreamsConfig to validate configs & check for application.id
>         final StreamsConfig config = new StreamsConfig(props); 
>         return new StreamsBuilder(config);
>     }
> }{code}
>  
> This should satisfy both of the requirements, and imo provides a cleaner API anyways. Getting the builder through a factory method on the KafkaStreams object should make it clear that this builder is tied to that particular KafkaStreams instance. And we can enforce that it isn't reused for a different application by parsing the Properties passed in to KafkaStreams#newTopologyBuilder, specifically the application.id



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