Status
Current state: Under Discussion
Discussion thread: [DISCUSS] KIP-120: Cleanup Kafka Streams builder API
JIRA: KAFKA-3856
Released: 0.10.3
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Motivation
Currently, Kafka Streams public API leaks a bunch of internal methods that should not be public. Furthermore, DSL and PAPI abstraction are not completely separated at the moment and TopologyBuilder
offers methods that belong to DSL only.
Public Interfaces
In order to get a clean refactoring, we will deprecate classes
org.apache.kafka.streams.processor.TopologyBuilder
org.apache.kafka.streams.kstream.
KStreamBuilder
and add them again (with new name and different package)
org.apache.kafka.streams.Topology
org.apache.kafka.streams.
KStreamBuilderorg.apache.kafka.streams.TopologyDescription
TopologyDescription
will have public subclassesSubtopology
GlobalStores
Node
(interface)Source
Sink
Processor
The following methods will not be available in the newly added classes:
TopologyBuilder
: setApplicationId, connectSourceStoreAndTopic, connectProcessors, addInternalTopic, copartitionSources, nodeGroups, build, buildGlobalStateTopology, globalStateStores, topicGroups, earliestResetTopicPattern, latestResetTopicPattern, stateStoreNamesToSourceTopics, copartitioneGroups, sourceTopicPattern, updateSubscriptionsKStreamBuilder
: all from TopologyBuilder except addStateStore and addGlobalStore (as KStreamBuilder does not inherit from TopologyBuilder anymore) plus newName- methods highlighted in
TopologyBuilder
list, are methods that actually belong to DSL abstraction
New org.apache.kafka.streams.Topology
class:
public class Topology { // existing public API from current TopologyBuilder class that will not be changed public enum AutoOffsetReset { EARLIEST , LATEST } public Topology(); public synchronized Topology addSource(String name, String... topics); public synchronized Topology addSource(String name, Pattern topicPattern); public synchronized Topology addSource(AutoOffsetReset offsetReset, String name, String... topics); public synchronized Topology addSource(AutoOffsetReset offsetReset, String name, Pattern topicPattern); public synchronized Topology addSource(String name, Deserializer keyDeserializer, Deserializer valDeserializer, String... topics); public synchronized Topology addSource(String name, Deserializer keyDeserializer, Deserializer valDeserializer, Pattern topicPattern); public synchronized Topology addSource(AutoOffsetReset offsetReset, String name, Deserializer keyDeserializer, Deserializer valDeserializer, String... topics); public synchronized Topology addSource(AutoOffsetReset offsetReset, String name, Deserializer keyDeserializer, Deserializer valDeserializer, Pattern topicPattern; public synchronized Topology addSink(String name, String topic, String... parentNames); public synchronized Topology addSink(String name, String topic, Serializer keySerializer, Serializer valSerializer, String... parentNames); public synchronized Topology addSink(String name, String topic, StreamPartitioner partitioner, String... parentNames); public synchronized <K, V> Topology addSink(String name, String topic, Serializer<K> keySerializer, Serializer<V> valSerializer, StreamPartitioner<? super K, ? super V> partitioner, String... parentNames); public synchronized Topology addProcessor(String name, ProcessorSupplier supplier, String... parentNames); public synchronized Topology addStateStore(StateStoreSupplier supplier, String... processorNames); public synchronized Topology addGlobalStore(final StateStore store, final String sourceName, final Deserializer keyDeserializer, final Deserializer valueDeserializer, final String topic, final String processorName, final ProcessorSupplier stateUpdateSupplier); public synchronized Topology connectProcessorAndStateStores(String processorName, String... stateStoreNames); // newly added method to reveal topology structure public synchronized TopologyDescription describe(); }
New org.apache.kafka.streams.KStreamBuilder
class:
public class KStreamBuilder { // existing public API from current KStreamBuilder class that will not be changed // small change: adding `synchronized` to all methods to align with TopologyBuilder public KStreamBuilder(); public synchronized <K, V> KStream<K, V> stream(final String... topics); public synchronized <K, V> KStream<K, V> stream(final Pattern topicPattern); public synchronized <K, V> KStream<K, V> stream(final AutoOffsetReset offsetReset, final String... topics); public synchronized <K, V> KStream<K, V> stream(final AutoOffsetReset offsetReset, final Pattern topicPattern); public synchronized <K, V> KStream<K, V> stream(final Serde<K> keySerde, final Serde<V> valSerde, final String... topics); public synchronized <K, V> KStream<K, V> stream(final Serde<K> keySerde, final Serde<V> valSerde, final Pattern topicPattern); public synchronized <K, V> KStream<K, V> stream(final AutoOffsetReset offsetReset, final Serde<K> keySerde, final Serde<V> valSerde, final String... topics); public synchronized <K, V> KStream<K, V> stream(final AutoOffsetReset offsetReset, final Serde<K> keySerde, final Serde<V> valSerde, final Pattern topicPattern); public synchronized <K, V> KTable<K, V> table(final String topic, final String storeName); public synchronized <K, V> KTable<K, V> table(final AutoOffsetReset offsetReset, final String topic, final String storeName); public synchronized <K, V> KTable<K, V> table(final Serde<K> keySerde, final Serde<V> valSerde, final String topic, final String storeName); public synchronized <K, V> KTable<K, V> table(final AutoOffsetReset offsetReset, final Serde<K> keySerde, final Serde<V> valSerde, final String topic, final String storeName); public synchronized <K, V> GlobalKTable<K, V> globalTable(final String topic, final String storeName); public synchronized <K, V> GlobalKTable<K, V> globalTable(final Serde<K> keySerde, final Serde<V> valSerde, final String topic, final String storeName); public synchronized <K, V> KStream<K, V> merge(final KStream<K, V>... streams); // newly added method public synchronized KStreamBuilder addStateStore(StateStoreSupplier supplier, String... processorNames); public synchronized KStreamBuilder addGlobalStore(final StateStore store, final String sourceName, final Deserializer keyDeserializer, final Deserializer valueDeserializer, final String topic, final String processorName, final ProcessorSupplier stateUpdateSupplier); public synchronized Topology build(); }
New org.apache.kafka.streams.TopologyDescription
class:
public final class TopologyDescription { public final List<Subtopology> subtopologies; public final List<GlobalStore> globalStores; public final class Subtopology { public final List<Node> nodes; } public final class GlobalStore { public final String name; public final String topic; } public interface Node { List<Node> getPredecessors(); List<Node> getSuccessors(); } public final class Source implements Node { public final String name; public final String topic; // can be topic name or pattern (as String) } public final class Processor implements Node { public final String name; public final List<String> stores; } public final class Sink implements Node { public final String name; public final String topic; } }
Changes to org.apache.kafka.streams.KafkaStreams
:
public class KafkaStreams { // deprecating old constructors @Deprecated public KafkaStreams(final TopologyBuilder builder, final Properties props); @Deprecated public KafkaStreams(final TopologyBuilder builder, final StreamsConfig config); @Deprecated public KafkaStreams(final TopologyBuilder builder, final StreamsConfig config, final KafkaClientSupplier clientSupplier); // adding new constructors public KafkaStreams(final Topology builder, final Properties props); public KafkaStreams(final Topology builder, final StreamsConfig config); public KafkaStreams(final Topology builder, final StreamsConfig config, final KafkaClientSupplier clientSupplier); }
Proposed Changes
Refactor the code to remove internal methods from public API.
We will add two new internal classes
org.apache.kafka.streams.processor.internals.InternalTopologyBuilder
org.apache.kafka.streams.kstream.internals.InternalKStreamBuilder
that offer the methods remove from current API. Thus, both classes are the actual implementation. Old TopologyBuilder
and KStreamBuilder
are only proxy classes to both classes respectively, for backward compatibility.
The newly added Topology
uses InternalTopologyBuilder
as member.
The newly added KStreamBuilder
used the new TopologyBuilder
as a member (no class hierarchy anymore – using it as member gives a clear separation between PAPI and DSL).
Because the new KStreamBuilder
does not inherit from new TopologyBuilder
we need to add some more constructors to KafkaStreams
.
Note: because of backward compatibility, removed DSL specific classes offered by old TopologyBuilder
must be offered by InternalTopologyBuilder
for now. However, after both deprecated classes got removed, this cleanup can be done (and does not require a KIP anymore, because it's internal refactoring -- we just need to create a JIRA for this). Thus, this KIP falls short of separating PAPI and DSL completely. But it's a necessary first step to do the separation in a backward compatible way (backward compatibility requires a two step approach).
Compatibility, Deprecation, and Migration Plan
- Because no classes/method will be removed but only deprecated, this change will be fully backward compatible
- We intend to remove all deprecated classes/methods in 0.10.4, but we can keep them longer on user request
Test Plan
Test need to be rewritten but no new tests are required. All tests for public API need to be updated to use new TopologyBuilder
and KStreamBuilder
, and thus will not call deprecated KafkaStreams
constructor anymore. All tests using internal API, need to be rewritten to use InternalTopologyBuilder
and InternalKStreamBuilder
.
Rejected Alternatives
None.