org.apache.flink.streaming.connectors.kinesis

Class FlinkKinesisConsumer<T>

java.lang.Object

org.apache.flink.api.common.functions.AbstractRichFunction

org.apache.flink.streaming.api.functions.source.RichParallelSourceFunction<T>

org.apache.flink.streaming.connectors.kinesis.FlinkKinesisConsumer<T>

Type Parameters:

T - the type of data emitted

All Implemented Interfaces:

Serializable, Function, RichFunction, ResultTypeQueryable<T>, CheckpointedFunction, ParallelSourceFunction<T>, SourceFunction<T>

Direct Known Subclasses:

FlinkDynamoDBStreamsConsumer

@PublicEvolving
public class FlinkKinesisConsumer<T>
extends RichParallelSourceFunction<T>
implements ResultTypeQueryable<T>, CheckpointedFunction

The Flink Kinesis Consumer is an exactly-once parallel streaming data source that subscribes to multiple AWS Kinesis streams within the same AWS service region, and can handle resharding of streams. Each subtask of the consumer is responsible for fetching data records from multiple Kinesis shards. The number of shards fetched by each subtask will change as shards are closed and created by Kinesis.

To leverage Flink's checkpointing mechanics for exactly-once streaming processing guarantees, the Flink Kinesis consumer is implemented with the AWS Java SDK, instead of the officially recommended AWS Kinesis Client Library, for low-level control on the management of stream state. The Flink Kinesis Connector also supports setting the initial starting points of Kinesis streams, namely TRIM_HORIZON and LATEST.

Kinesis and the Flink consumer support dynamic re-sharding and shard IDs, while sequential, cannot be assumed to be consecutive. There is no perfect generic default assignment function. Default shard to subtask assignment, which is based on hash code, may result in skew, with some subtasks having many shards assigned and others none.

It is recommended to monitor the shard distribution and adjust assignment appropriately. A custom assigner implementation can be set via setShardAssigner(KinesisShardAssigner) to optimize the hash function or use static overrides to limit skew.

In order for the consumer to emit watermarks, a timestamp assigner needs to be set via setPeriodicWatermarkAssigner(AssignerWithPeriodicWatermarks) and the auto watermark emit interval configured via ExecutionConfig.setAutoWatermarkInterval(long).

Watermarks can only advance when all shards of a subtask continuously deliver records. To avoid an inactive or closed shard to block the watermark progress, the idle timeout should be configured via configuration property ConsumerConfigConstants.SHARD_IDLE_INTERVAL_MILLIS. By default, shards won't be considered idle and watermark calculation will wait for newer records to arrive from all shards.

Note that re-sharding of the Kinesis stream while an application (that relies on the Kinesis records for watermarking) is running can lead to incorrect late events. This depends on how shards are assigned to subtasks and applies regardless of whether watermarks are generated in the source or a downstream operator.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.flink.streaming.api.functions.source.SourceFunction

SourceFunction.SourceContext<T>

Constructor Summary

Constructors

Constructor and Description
FlinkKinesisConsumer(List<String> streams, KinesisDeserializationSchema<T> deserializer, Properties configProps) Creates a new Flink Kinesis Consumer.
FlinkKinesisConsumer(String stream, DeserializationSchema<T> deserializer, Properties configProps) Creates a new Flink Kinesis Consumer.
FlinkKinesisConsumer(String stream, KinesisDeserializationSchema<T> deserializer, Properties configProps) Creates a new Flink Kinesis Consumer.

Method Summary

Modifier and Type	Method and Description
void	cancel() Cancels the source.
void	close() Tear-down method for the user code.
protected KinesisDataFetcher<T>	createFetcher(List<String> streams, SourceFunction.SourceContext<T> sourceContext, RuntimeContext runtimeContext, Properties configProps, KinesisDeserializationSchema<T> deserializationSchema) This method is exposed for tests that need to mock the KinesisDataFetcher in the consumer.
AssignerWithPeriodicWatermarks<T>	getPeriodicWatermarkAssigner()
TypeInformation<T>	getProducedType() Gets the data type (as a TypeInformation) produced by this function or input format.
KinesisShardAssigner	getShardAssigner()
WatermarkTracker	getWatermarkTracker()
void	initializeState(FunctionInitializationContext context) This method is called when the parallel function instance is created during distributed execution.
void	run(SourceFunction.SourceContext<T> sourceContext) Starts the source.
void	setPeriodicWatermarkAssigner(AssignerWithPeriodicWatermarks<T> periodicWatermarkAssigner) Set the assigner that will extract the timestamp from T and calculate the watermark.
void	setShardAssigner(KinesisShardAssigner shardAssigner) Provide a custom assigner to influence how shards are distributed over subtasks.
void	setWatermarkTracker(WatermarkTracker watermarkTracker) Set the global watermark tracker.
void	snapshotState(FunctionSnapshotContext context) This method is called when a snapshot for a checkpoint is requested.

Methods inherited from class org.apache.flink.api.common.functions.AbstractRichFunction

getIterationRuntimeContext, getRuntimeContext, open, setRuntimeContext

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FlinkKinesisConsumer

public FlinkKinesisConsumer(String stream,
                            DeserializationSchema<T> deserializer,
                            Properties configProps)

Creates a new Flink Kinesis Consumer.

The AWS credentials to be used, AWS region of the Kinesis streams, initial position to start streaming from are configured with a Properties instance.

Parameters:

stream - The single AWS Kinesis stream to read from.

deserializer - The deserializer used to convert raw bytes of Kinesis records to Java objects (without key).

configProps - The properties used to configure AWS credentials, AWS region, and initial starting position.

FlinkKinesisConsumer

public FlinkKinesisConsumer(String stream,
                            KinesisDeserializationSchema<T> deserializer,
                            Properties configProps)

Creates a new Flink Kinesis Consumer.

The AWS credentials to be used, AWS region of the Kinesis streams, initial position to start streaming from are configured with a Properties instance.

Parameters:

stream - The single AWS Kinesis stream to read from.

deserializer - The keyed deserializer used to convert raw bytes of Kinesis records to Java objects.

configProps - The properties used to configure AWS credentials, AWS region, and initial starting position.

FlinkKinesisConsumer

public FlinkKinesisConsumer(List<String> streams,
                            KinesisDeserializationSchema<T> deserializer,
                            Properties configProps)

Creates a new Flink Kinesis Consumer.

The AWS credentials to be used, AWS region of the Kinesis streams, initial position to start streaming from are configured with a Properties instance.

Parameters:

streams - The AWS Kinesis streams to read from.

deserializer - The keyed deserializer used to convert raw bytes of Kinesis records to Java objects.

configProps - The properties used to configure AWS credentials, AWS region, and initial starting position.

Method Detail

getShardAssigner

public KinesisShardAssigner getShardAssigner()

setShardAssigner

public void setShardAssigner(KinesisShardAssigner shardAssigner)

Provide a custom assigner to influence how shards are distributed over subtasks.

Parameters:

shardAssigner - shard assigner

getPeriodicWatermarkAssigner

public AssignerWithPeriodicWatermarks<T> getPeriodicWatermarkAssigner()

setPeriodicWatermarkAssigner

public void setPeriodicWatermarkAssigner(AssignerWithPeriodicWatermarks<T> periodicWatermarkAssigner)

Set the assigner that will extract the timestamp from T and calculate the watermark.

Parameters:

periodicWatermarkAssigner - periodic watermark assigner

getWatermarkTracker

public WatermarkTracker getWatermarkTracker()

setWatermarkTracker

public void setWatermarkTracker(WatermarkTracker watermarkTracker)

Set the global watermark tracker. When set, it will be used by the fetcher to align the shard consumers by event time.

Parameters:

watermarkTracker -

run

public void run(SourceFunction.SourceContext<T> sourceContext)
         throws Exception

Description copied from interface: SourceFunction

Starts the source. Implementations use the SourceFunction.SourceContext to emit elements. Sources that checkpoint their state for fault tolerance should use the SourceFunction.SourceContext.getCheckpointLock() checkpoint lock} to ensure consistency between the bookkeeping and emitting the elements.

Sources that implement CheckpointedFunction must lock on the SourceFunction.SourceContext.getCheckpointLock() checkpoint lock} checkpoint lock (using a synchronized block) before updating internal state and emitting elements, to make both an atomic operation.

Refer to the top-level class docs for an example.

Specified by:

run in interface SourceFunction<T>

Parameters:

sourceContext - The context to emit elements to and for accessing locks.

Throws:

Exception

cancel

public void cancel()

Description copied from interface: SourceFunction

Cancels the source. Most sources will have a while loop inside the SourceFunction.run(SourceContext) method. The implementation needs to ensure that the source will break out of that loop after this method is called.

A typical pattern is to have an "volatile boolean isRunning" flag that is set to false in this method. That flag is checked in the loop condition.

In case of an ungraceful shutdown (cancellation of the source operator, possibly for failover), the thread that calls SourceFunction.run(SourceContext) will also be interrupted) by the Flink runtime, in order to speed up the cancellation (to ensure threads exit blocking methods fast, like I/O, blocking queues, etc.). The interruption happens strictly after this method has been called, so any interruption handler can rely on the fact that this method has completed (for example to ignore exceptions that happen after cancellation).

During graceful shutdown (for example stopping a job with a savepoint), the program must cleanly exit the SourceFunction.run(SourceContext) method soon after this method was called. The Flink runtime will NOT interrupt the source thread during graceful shutdown. Source implementors must ensure that no thread interruption happens on any thread that emits records through the SourceContext from the SourceFunction.run(SourceContext) method; otherwise the clean shutdown may fail when threads are interrupted while processing the final records.

Because the SourceFunction cannot easily differentiate whether the shutdown should be graceful or ungraceful, we recommend that implementors refrain from interrupting any threads that interact with the SourceContext at all. You can rely on the Flink runtime to interrupt the source thread in case of ungraceful cancellation. Any additionally spawned threads that directly emit records through the SourceContext should use a shutdown method that does not rely on thread interruption.

Specified by:

cancel in interface SourceFunction<T>

close

public void close()
           throws Exception

Description copied from interface: RichFunction

Tear-down method for the user code. It is called after the last call to the main working methods (e.g. map or join). For functions that are part of an iteration, this method will be invoked after each iteration superstep.

This method can be used for clean up work.

Specified by:

close in interface RichFunction

Overrides:

close in class AbstractRichFunction

Throws:

Exception - Implementations may forward exceptions, which are caught by the runtime. When the runtime catches an exception, it aborts the task and lets the fail-over logic decide whether to retry the task execution.

getProducedType

public TypeInformation<T> getProducedType()

Description copied from interface: ResultTypeQueryable

Gets the data type (as a TypeInformation) produced by this function or input format.

Specified by:

getProducedType in interface ResultTypeQueryable<T>

Returns:

The data type produced by this function or input format.

initializeState

public void initializeState(FunctionInitializationContext context)
                     throws Exception

Description copied from interface: CheckpointedFunction

This method is called when the parallel function instance is created during distributed execution. Functions typically set up their state storing data structures in this method.

Specified by:

initializeState in interface CheckpointedFunction

Parameters:

context - the context for initializing the operator

Throws:

Exception - Thrown, if state could not be created ot restored.

snapshotState

public void snapshotState(FunctionSnapshotContext context)
                   throws Exception

Description copied from interface: CheckpointedFunction

This method is called when a snapshot for a checkpoint is requested. This acts as a hook to the function to ensure that all state is exposed by means previously offered through FunctionInitializationContext when the Function was initialized, or offered now by FunctionSnapshotContext itself.

Specified by:

snapshotState in interface CheckpointedFunction

Parameters:

context - the context for drawing a snapshot of the operator

Throws:

Exception - Thrown, if state could not be created ot restored.

createFetcher

protected KinesisDataFetcher<T> createFetcher(List<String> streams,
                                              SourceFunction.SourceContext<T> sourceContext,
                                              RuntimeContext runtimeContext,
                                              Properties configProps,
                                              KinesisDeserializationSchema<T> deserializationSchema)

This method is exposed for tests that need to mock the KinesisDataFetcher in the consumer.