Data Stream Processing with Apache Flink

Data Stream Processing with
Apache Flink
Fabian Hueske
@fhueske
Apache Flink Meetup Madrid, 25.02.2016

What is Apache Flink?
Apache Flink is an open source platform for
scalable stream and batch processing.
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• The core of Flink is a distributed
streaming dataflow engine.
• Executes dataflows in
parallel on clusters
• Provides a reliable backend
for various workloads
• DataStream and DataSet
programming abstractions are
the foundation for user programs
and higher layers

What is Apache Flink?
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Streaming topologies
Long batch pipelines
Machine Learning at scale
A stream processor with many faces
Graph Analysis
 resource utilization
 iterative algorithms
 Mutable state
 low-latency processing

History & Community of Flink
From incubation until now
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5
Apr ‘14 Jun ‘15Dec ‘14
0.70.60.5 0.9 0.10
Nov ‘15
Top level
0.8
Mar ‘15
1.0!

Growing and Vibrant Community
Flink is one of the largest and most active Apache big data projects:
• more than 150 contributors
• more than 600 forks
• more than 1000 Github stars (since yesterday)
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Flink Meetups around the Globe
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Flink Meetups around the Globe
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✔ 

Organizations at Flink Forward
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The streaming era
Coming soon…
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What is Stream Processing?
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 Today, most data is continuously produced
• user activity logs, web logs, sensors, database
transactions, …
 The common approach to analyze such data so far
• Record data stream to stable storage (DBMS, HDFS, …)
• Periodically analyze data with batch processing engine
(DBMS, MapReduce, ...)
 Streaming processing engines analyze data
while it arrives

Why do Stream Processing?
 Decreases the overall latency to obtain results
• No need to persist data in stable storage
• No periodic batch analysis jobs
 Simplifies the data infrastructure
• Fewer moving parts to be maintained and coordinated
 Makes time dimension of data explicit
• Each event has a timestamp
• Data can be processed based on timestamps
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What are the Requirements?
 Low latency
• Results in millisecond
 High throughput
• Millions of events per second
 Exactly-once consistency
• Correct results in case of failures
 Out-of-order events
• Process events based on their associated time
 Intuitive APIs
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OS Stream Processors so far
 Either low latency or high throughput
 Exactly-once guarantees only with high latency
 Lacking time semantics
• Processing by wall clock time only
• Events are processed in arrival order, not in the order they were
created
 Shortcomings lead to complicated system designs
• Lambda architecture
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Stream Processing with Flink
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Stream Processing with Flink
 Low latency
• Pipelined processing engine
 High throughput
• Controllable checkpointing overhead
 Exactly-once guarantees
• Distributed snapshots
 Support for out-of-order streams
• Processing semantics based on event-time
 Programmability
• APIs similar to those known from the batch world
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Flink in Streaming Architectures
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Flink
Flink Flink
Elasticsearch, Hbase,
Cassandra, …
HDFS
Kafka
Analytics on static data
Data ingestion
and ETL
Analytics on data
in motion

The DataStream API
Concise and easy-to-grasp code
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The DataStream API
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case class Event(location: Location, numVehicles: Long)
val stream: DataStream[Event] = …;
stream
.filter { evt => isIntersection(evt.location) }

The DataStream API
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stream
.keyBy("location")
.timeWindow(Time.minutes(15), Time.minutes(5))
.sum("numVehicles")

The DataStream API
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stream
.keyBy("location")
.timeWindow(Time.minutes(15), Time.minutes(5))
.sum("numVehicles")
.keyBy("location")
.mapWithState { (evt, state: Option[Model]) => {
val model = state.orElse(new Model())
(model.classify(evt), Some(model.update(evt)))
}}

Event-time processing
Consistent and sound results
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Event-time Processing
 Most data streams consist of events
• log entries, sensor data, user actions, …
• Events have an associated timestamp
 Many analysis tasks are based on time
• “Average temperature every minute”
• “Count of processed parcels per hour”
• ...
 Events often arrive out-of-order at processor
• Distributed sources, network delays, non-synced clocks, …
 Stream processor must respect time of events for
consistent and sound results
• Most stream processors use wall clock time
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Event Processing
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Events occur on devices
Queue / Log
Events analyzed in a
stream processor
Stream Analysis
Events stored in a log

Event Processing
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Out of order!!!
First burst of events
Second burst of events

Event Processing
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Event time windows
Arrival time windows
Instant event-at-a-time
Flink supports out-of-order streams (event time) windows,
arrival time windows (and mixtures) plus low latency processing.
First burst of events
Second burst of events

Event-time Processing
 Event-time processing decouples job semantics
from processing speed
 Analyze events from static data store and
online stream using the same program
 Semantically sound and consistent results
 Details:
http://data-artisans.com/how-apache-flink-enables-new-
streaming-applications-part-1
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Operational Features
Running Flink 24*7*52
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Monitoring & Dashboard
 Many metrics exposed via REST interface
 Web dashboard
• Submit, stop, and cancel jobs
• Inspect running and completed jobs
• Analyze performance
• Check exceptions
• Inspect configuration
• …
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Highly-available Cluster Setup
 Stream applications run for weeks, months, …
• Application must never fail!
• No single-point-of-failure component allowed
 Flink supports highly-available cluster setups
• Master failures are resolved using Apache Zookeeper
• Worker failures are resolved by master
 Stand-alone cluster setup
• Requires (manually started) stand-by masters and workers
 YARN cluster setup
• Masters and workers are automatically restarted
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 A save point is a consistent snapshot of a job
• Includes source offsets and operator state
• Stop job
• Restart job from save point
 What can I use it for?
• Fix or update your job
• A/B testing
• Update Flink
• Migrate cluster
• …
 Details:
http://data-artisans.com/how-apache-flink-enables-new-
streaming-applications
Save Points
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Performance: Summary
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Continuous
streaming
Latency-bound
buffering
Distributed
Snapshots
High Throughput &
Low Latency
With configurable throughput/latency tradeoff
Details:
http://data-artisans.com/high-throughput-low-latency-
and-exactly-once-stream-processing-with-apache-flink

Integration (picture not complete)
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POSIX Java/Scala
Collections
POSIX

Post v1.0 Roadmap
What’s coming next?
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Stream SQL and Table API
 Structured queries over data streams
• LINQ-style Table API
• Stream SQL
 Based on Apache Calcite
• SQL Parser and optimizer
 “Compute every hour the number of orders and
number ordered units for each product.”
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SELECT STREAM
productId,
TUMBLE_END(rowtime, INTERVAL '1' HOUR) AS rowtime,
COUNT(*) AS cnt,
SUM(units) AS units
FROM
Orders
GROUP BY
TUMBLE(rowtime, INTERVAL '1' HOUR),
productId;

Complex Event Processing
 Identify complex patterns in event streams
• Correlations & sequences
 Many applications
• Network intrusion detection via access patterns
• Item tracking (parcels, devices, …)
• …
 CEP depends on low latency processing
• Most CEP system are not distributed
 CEP in Flink
• Easy-to-use API to define CEP patterns
• Integration with Table API for structured analytics
• Low-latency and high-throughput engine
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Dynamic Job Parallelism
 Adjusting parallelism of tasks without (significantly)
interrupting the program
 Initial version based on save points
• Trigger save point
• Stop job
• Restart job with adjusted parallelism
 Later change parallelism while job is running
 Vision is automatic adaption based on throughput
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Wrap up!
 Flink is a kick-ass stream processor…
• Low latency & high throughput
• Exactly-once consistency
• Event-time processing
• Support for out-of-order streams
• Intuitive API
 with lots of features in the pipeline…
 and a reliable batch processor as well!
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I ♥ Squirrels, do you?
 More Information at
• http://flink.apache.org/
 Free Flink training at
• http://dataartisans.github.io/flink-training
 Sign up for user/dev mailing list
 Get involved and contribute
 Follow @ApacheFlink on Twitter
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