Status
Current state: Under Discussion
Discussion thread: [DISCUSS] KIP-120: Cleanup Kafka Streams builder API
JIRA: KAFKA-3856
Released: 0.11.0
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.
StreamsTopologyBuilder
Furthermore, we add a new class to get a full description the a topology (to compensate for some internal methods that get removed)
org.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 -> Topology
: setApplicationId, connectSourceStoreAndTopic, connectProcessors, addInternalTopic, copartitionSources, nodeGroups, build, buildGlobalStateTopology, globalStateStores, topicGroups, earliestResetTopicPattern, latestResetTopicPattern, stateStoreNamesToSourceTopics, copartitioneGroups, sourceTopicPattern, updateSubscriptionsKStreamBuilder -> StreamsTopologyBuilder
: all methods from TopologyBuilder (as KStreamBuilder does not inherit from TopologyBuilder anymore) except addStateStore and addGlobalStore (which are both added explicitly toStreamsTopologyBuilder
) 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 // describes the current Topology, ie, TopologyDescription will not be updated if Topology is modified but #describe() must be called again public synchronized TopologyDescription describe(); }
New org.apache.kafka.streams.StreamTopologyBuilder
class:
public class StreamsTopologyBuilder { // existing public API from current KStreamBuilder class that will not be changed // small change: adding `synchronized` to all methods to align with TopologyBuilder public StreamsTopologyBuilder(); 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; String topics; // can be comma separated list of topic names 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; } }
Proposed Changes
We will add two new internal classes
org.apache.kafka.streams.processor.internals.InternalTopologyBuilder
org.apache.kafka.streams.kstream.internals.InternalStreamsTopologyBuilder
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 StreamsTopologyBuilder
uses the new Topology
as a member (no class hierarchy anymore – using it as member gives a clear separation between PAPI and DSL).
Because the new StreamsTopologyBuilder
does not inherit from new Topology
we need to add StreamsTopologyBuilder#build()
that returns the actual Topology
to be passed into KafkaStreams
client.
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 0.11.1, but we can keep them longer on user request
Test Plan
Tests need to be rewritten but no new tests are required. All tests for public API need to be updated to use new Topology
and StreamsTopologyBuilder
. All tests using internal API, need to be rewritten to use InternalTopologyBuilder
and InternalStreamsTopologyBuilder
.
Rejected Alternatives
None.