Lessons Learned: Using Spark and Microservices to Empower Data Scientists and Data Engineers

1. LESSONS LEARNED:
USING SPARK AND MICROSERVICES
(TO EMPOWER DATA SCIENTISTS AND DATA ENGINEERS)
Alexis Seigneurin

2. Who I am
• Software engineer for 15+ years
• Consultant at Ippon USA, previously at Ippon France
• Favorite subjects: Spark, Machine Learning, Cassandra
• Spark trainer
• @aseigneurin

3. • 200 software engineers in France, the US and Australia
• In the US: offices in DC, NYC and Richmond,Virginia
• Digital, Big Data and Cloud applications
• Java & Agile expertise
• Open-source projects: JHipster,Tatami, etc.
• @ipponusa

4. The project
• Analyze records from customers → Give feedback to the customer on their data
• High volume of data
• 25 millions records per day (average)
• Need to keep at least 60 days of history = 1.5 Billion records
• Seasonal peaks...
• Need an hybrid platform
• Batch processing for some types of analysis
• Streaming for other analyses
• Hybrid team
• Data Scientists: more familiar with Python
• Software Engineers: Java

5. Technical Overview

6. Processing technology - Spark
• Mature platform
• Supports batch jobs and streaming jobs
• Support for multiple programming languages
• Python → Data Scientists
• Scala/Java → Software Engineers

7. Architecture - Real time platform
• New use cases are implemented by Data Scientists all the time
• Need the implementations to be independent from each other
• One Spark Streaming job per use case
• Microservice-inspired architecture
• Diamond-shaped
• Upstream jobs are written in Scala
• Core is made of multiple Python jobs, one per use case
• Downstream jobs are written in Scala
• Plumbing between the jobs → Kafka
1/2

8. Architecture - Real time platform 2/2

9. Messaging technology - Kafka
From kafka.apache.org
• “A high-throughput distributed messaging system”
• Messaging: between 2 Spark jobs
• Distributed: fits well with Spark, can be scaled up or down
• High-throughput: so as to handle an average of 300 messages/second, peaks at 2000 m/s
• “Apache Kafka is publish-subscribe messaging rethought as a distributed
commit log”
• Commit log so that you can go back in time and reprocess data
• Only used as such when a job crashes, for resilience purposes

10. Storage
• Currently PostgreSQL:
• SQL databases are well known by developers and easy to work with
• PostgreSQL is available “as-a-service” on AWS
• Working on transitioning to Cassandra (more on that
later)

11. Deployment platform
• Amazon AWS
• Company standard - Everything in the cloud
• Easy to scale up or down, ability to choose the hardware
• Some limitations
• Requirement to use company-crafted AMIs
• Cannot use some services (EMR…)
• AMIs are renewed every 2 months → need to recreate the platform
continuously

12. Strengths of the platform

13. Modularity
• One Spark job per use case
• Hot deployments: can roll out new use cases (= new jobs) without
stopping existing jobs
• Can roll out updated code without affecting other jobs
• Able to measure the resources consumed by a single job
• Shared services are provided by upstream and
downstream jobs

14. A/B testing
• A/B testing of updated features
• Run 2 implementations of the code in parallel
• Let each filter process the data of all the customers
• Post-filter to let the customers receive A or B
• (Measure…)
• Can be used to slowly roll out new features

15. Data Scientists can contribute
• Spark in Python → pySpark
• Data Scientists know Python (and don’t want to hear about Java/
Scala!)
• Business logic implemented in Python
• Code is easy to write and to read
• Data Scientists are real contributors → quick iterations to production

16. Challenges

17. Data Scientist code in production
• Shipping code written by Data Scientists is not ideal
• Need production-grade code (error handling, logging…)
• Code is less tested than Scala code
• Harder to deploy than a JAR file → PythonVirtual Environments
• blog.cloudera.com/blog/2015/09/how-to-prepare-your-apache-
hadoop-cluster-for-pyspark-jobs/

18. Allocation of resources in Spark
• With Spark Streaming, resources (CPU & memory) are allocated per job
• Resources are allocated when the job is submitted and cannot be updated on the
fly
• Have to allocate 1 core to the Driver of the job → unused resource
• Have to allocate extra resources to each job to handle variations in traffic →
unused resources
• For peak periods, easy to add new Spark Workers but jobs have to restarted
• Idea to be tested:
• Over allocation of real resources, e.g let Spark know it has 6 cores on a 4-cores server

19. Micro-batches
Spark streaming processes events in micro-batches
• Impact on the latency
• Spark Streaming micro-batches → hard to achieve sub-second latency
• See spark.apache.org/docs/latest/streaming-programming-guide.html#task-launching-overheads
• Total latency of the system = sum of the latencies of each stage
• In this use case, events are independent from each other - no need for windowing computation → a
real streaming framework would be more appropriate
• Impact on memory usage
• Kafka+Spark using the direct approach = 1 RDD partition per Kafka partition
• If you start the Spark with lots of unprocessed data in Kafka, RDD partitions can exceed the size of
the memory

20. Resilience of Spark jobs
• Spark Streaming application = 1 Driver + 1 Application
• Application = N Executors
• If an Executor dies → restarted (seamless)
• If the Driver dies, the whole Application must be restarted
• Scala/Java jobs → “supervised” mode
• Python jobs → not supported with Spark Standalone

21. Resilience with Spark & Kafka
• Connecting Spark to Kafka, 2 methods:
• Receiver-based approach: not ideal for parallelism
• Direct approach: better for parallelism but have to deal with Kafka offsets
• Dealing with Kafka offsets
• Default: consumes from the end of the Kafka topic (or the beginning)
• Documentation → Use checkpoints
• Tasks have to be Serializable (not always possible: dependent libraries)
• Harder to deploy the application (classes are serialized) → run a new instance in parallel and
kill the first one (harder to automate; messages consumed twice)
• Requires a shared file system (HDFS, S3) → big latency on these FS that forces to increase the
micro-batch interval
1/2

22. Resilience with Spark & Kafka
• Dealing with Kafka offsets
• Solution: deal with offsets in the Spark Streaming application
• Write the offsets to a reliable storage: ZooKeeper, Kafka…
• Write after processing the data
• Read the offsets on startup (if no offsets, start from the end)
• ippon.tech/blog/spark-kafka-achieving-zero-data-loss/
2/2

23. Writing to Kafka
• Spark Streaming comes with a library to read from Kafka
but none to write to Kafka!
• Flink or Kafka Streams do that out-of-the-box
• Cloudera provides an open-source library:
• github.com/cloudera/spark-kafka-writer
• (Has been removed by now!)

24. Idempotence
Spark and fault-tolerance semantics:
• Spark can provide exactly once guarantee only for the transformation
of the data
• Writing the data is at least once with non-transactional systems
(including Kafka in our case)
• See spark.apache.org/docs/latest/streaming-programming-
guide.html#fault-tolerance-semantics
→The overall system has to be idempotent

25. Message format & schemas
• Spark jobs are decoupled, but each depends on the upstream job
• Message formats have to be agreed upon
• JSON
• Pros: flexible
• Cons: flexible! (missing fields)
• Avro
• Pros: enforces a structure (named fields + types)
• Cons: hard to propagate the schemas
→ Confluent’s Schema Registry (more on that later)

26. Potential & upcoming
improvements

27. Confluent’s Schema Registry
docs.confluent.io/3.0.0/schema-registry/docs/index.html
• Separate (web) server to manage & enforce Avro schemas
• Stores schemas, versions them, and can perform compatibility checks
(configurable: backward or forward)
• Makes life simpler:
✓ no need to share schemas (“what version of the schema is this?”)
✓ no need to share generated classes
✓ can update the producer with backward-compatible messages without affecting the
consumers
1/2

28. Confluent’s Schema Registry
• Comes with:
• A Kafka Serializer (for the producer): sends the schema of the object to the Schema Registry before sending the record to Kafka
• Message sending fails if schema compatibility fails
• A Kafka Decoder (for the consumer): retrieves the schema from the Schema Registry when a message comes in
2/2

29. Kafka Streams
docs.confluent.io/3.0.0/streams/index.html
• “powerful, easy-to-use library for building highly scalable, fault-tolerant, distributed stream
processing applications on top of Apache Kafka”
• Perfect fit for micro-services on top of Kafka
• Natively consumes messages from Kafka
• Natively pushes produced messages to Kafka
• Processes messages one at a time → very low latency
1/2
• Pros
• API is very similar to Spark’s API
• Deploy new instances of the application to scale out
• Cons
• JVM languages only - no support for Python
• Outside of Spark - one more thing to manage

30. Kafka Streams
Properties props = new Properties();
props.put(StreamsConfig.APPLICATION_ID_CONFIG, "xxx");
props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9093");
props.put(StreamsConfig.ZOOKEEPER_CONNECT_CONFIG, "localhost:2182");
props.put(StreamsConfig.KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
props.put(StreamsConfig.VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "latest");
KStreamBuilder builder = new KStreamBuilder();
KStream<String, String> kafkaInput = builder.stream(“INPUT-TOPIC");
KStream<String, RealtimeXXX> auths = kafkaInput.mapValues(value -> ...);
KStream<String, byte[]> serializedAuths = auths.mapValues(a -> AvroSerializer.serialize(a));
serializedAuths.to(Serdes.String(), Serdes.ByteArray(), “OUTPUT-TOPIC");
KafkaStreams streams = new KafkaStreams(builder, props);
streams.start();
2/2
Example (Java)

31. Database migration
• The database stores the state
• Client settings or analyzed behavior
• Historical data (up to 60 days)
• Produced outputs
• Some technologies can store a state (e.g. Samza) but hardly 60 days of data
• Initially used PostgreSQL
• Easy to start with
• Available on AWS “as-a-service”: RDS
• Cannot scale to 60 days of historical data, though
• Cassandra is a good fit
• Scales out for the storage of historical data
• Connects to Spark
• Load Cassandra data into Spark, or saves data from Spark to Cassandra
• Can be used to reprocess existing data for denormalization purposes

32. Summary
&
Conclusion

33. Summary
Is the microservices architecture adequate?
• Interesting to separate the implementations of the use cases
• Overhead for the other services
Is Spark adequate?
• Supports Python (not supported by Kafka Streams)
• Micro-batches not adequate

34. Thank you!
@aseigneurin