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https://issues.apache.org/jira/browse/KAFKA-13336?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sagar Rao reassigned KAFKA-13336:
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Assignee: Sagar Rao
> 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
> Assignee: Sagar Rao
> 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. It also
> leads to a more natural process of writing a Kafka Streams app: start with
> the KafkaStreams object and global configs, then use this to build up the
> processing topology. Looking forward, this will better complement the new
> named topologies feature, with an API that treats topologies as entities
> attached to a particular KafkaStreams but that may come and go
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