- HiveHome provides smart home sensors that generate over 4 billion messages per day which are accessible through Kafka topics. - Many of HiveHome and Connected Home's services are based on analyzing this big data. - Lessons learned include decoupling applications, sticking to single responsibility principles, and making applications portable, immutable, and easy to test using Docker, Kubernetes, and other tools. - The data platform team replaced Spark jobs with Kafka Connect and KCQL to define extract and load stages generically with less duplication and improved reusability. - They are rethinking transformation stages using Kafka Streams instead of Spark for better performance and scalability without shared storage needs. - Data scientists at Connected

1. STREAMING 4 BILLIONS MESSAGES
LESSONS LEARNED
Angelos Petheriotis (@apetheriotis)
HiveHome

2. What is HiveHome doing ?
Provides a range of different sensors that all work together
to build a smart and connected home.

3. How is Big Data generated at Connected Home
…more devices to be released
How is it accessible ?
Avro messages through
Kafka Contracted topics
Some numbers ?
4+ Billion messages from input topics
to the Data Platform (increasing by 1000s every day)
Is it useful ?
Many of CH & BG services are based solely
on Big Data projects.

4. * design a micro services architecture
that won’t wake you up at 03:00 for a simple restart
* not duplicate stuff (code or configs)
significant % of our time we are plumbers ..let’s make our lives easy
* be resilient to failures.
Especially when dealing with stageful applications
* communicate/collaborate with data scientists
mathematicians != engineers
Processing 50K msgs/s from IoT Devices you learn to:

5. Try to :
* Decouple applications
* Stick to single responsibility principle
* Make apps portable
* Make apps immutable
* Make testing portable and easy
Docker & Kubernetes
GoCD (CI/CD)
Decouple ETL
Police EL with Schema Registry
Microservices in real time pipelines

6. Average the internal temperatures per
house per 30 minutes and persist to ES
Pros
* We only support/monitor one app !
* All in one place and you don’t have to
remember git repos etc..
Cons
* Job has 2 responsibilities
* Hard to test
* If we want to persist to Cassandra we
need to reprocess the messages
* We cannot reuse the app
Monolithic approach
T+ L

7. Pros
* 1 responsibility per app
* Easy to replace the load job to ES with
a Cassandra job
* Easy to replay data
* We CAN generalise/reuse the L stage
Cons
* We need to support/monitor 2 apps :(
Microsevices based approach
T E
E C*
ES

9. We went through of how our infrastructure looks like.
Let’s see what we deploy in that infrastructure

10. We used to write a lot of Spark apps for E & L operations
> internalTemperature to ElasticSearch
> internalTemperature Cassandra
> motionDetected to ElasticSearch
> deviceSignal to Cassandra
> …

11. But we replaced our spark jobs because…
We ended up with:
* Duplicated code all over the place for
simple tasks
* Too many github repos. Hard to keep them
in your head
* Too much time to provision a small cluster
to test the app
* Many resources £££ were wasted
because of the master/driver dependencies
of spark

12. The goal was to define the E & L stages *once* as
a generic re-usable component that handles:
Offset Management
Serialization / de-serialization
Partitioning / Scalability
Fault tolerance / fail-over
Schema Registry integration.

13. Kafka Connect to the rescue
Kafka Connect
* Suitable for EL operations (no T here)
* No driver/master/worker notations
* No dependency on zookeeper
* Uses the well tested kafka consumer/producers
* Configurable by a rest API

14. But by default you need to write some code for every application
for the specific domain transformations.

15. KCQL is a SQL like syntax allowing streamlined configuration of Kafka Sink Connectors
Examples:
* INSERT INTO transactionIndex SELECT * FROM transcationTopic
* INSERT INTO motionIndex SELECT motionDatetime As motionAt FROM motionTopic
KCQL (Kafka Connect Query Language)
Available operations: rename,ignore fields, reparation messages any many more
(https://github.com/datamountaineer/kafka-connect-query-language)

16. How it looks like today …

17. Monitor your KC apps…
* JMX Metrics and logs from the APP (Jmx metrics provide detailed granularity of the state of the KC app)
* Kafka Connect UI (logs and configs for each KC app available with 1 click - https://github.com/landoop)

18. E & L stages are now solid, well defined
with minimal duplication and highly reusable.
T needs some polishing. Time to re-think of
our T stage.

19. What was the problem …
Spark is great but not always the best option:
-> has the notation of micro batches
-> handling state is not optimal
-> you need shared storage to store checkpoints and state
-> you need a cluster with master, driver & workers
SPARK :(

20. From Spark to Kafka Streams …
Kafka Streams is great because:
-> is cluster and framework free
-> uses kafka to store the state
-> exposes the state via an API
-> has no notation of micro batches
-> KTables
-> No need for zookeeper

21. So we re-wrote one of our heavy CPU jobs in Kafka Streams
Results:
-> Again: No need to worry about where to store checkpoints. Everything is stored in kafka.
-> No need for a cluster. Just execute `java -jar app.jar`
-> Less scripting !
-> We needed to do funny stuff to make it work with scala :(

22. And now we have:
-> 50% less resources were used in some cases. Better CPU/Memory utilisation across instances.
-> Easier auto scaling. Just start more instances of your app and kafka streams will scale automatically.
-> Happier devops because they worry about the infrastructure and not the frameworks on top of that.
And since the state is exposed
through an API we now know
what happens internally inside the app at any given time

23. Until now we described the engineering part of the Data
Platform team.
Let’s see who uses the data from our platform.

24. Data Science @ HiveHome
Some of the projects:
-> Energy Breakdown
Distribute the energy usage into categories (lighting, cooking etc) just by knowing the total hourly
consumed energy (patent pending)
-> Heating Failure Alert
Try to identify if a boiler is not working properly, knowing only the internal temperature of a house

25. -> as much data as possible
-> as soon as possible
-> as accessible as possible
Data Science @ Connected Home
what do scientists need ?

26. Data Science @ Connected Home
how to work with data scientists
* Be proactive. Have the data ready in advance.
* Keep the data in an flexible datastore. I.e. Elastic Search and not Cassandra.
* Side by side development during each iteration of a model. (Scientists do not unit test!)
* Jupyter/Zeppelin notebooks. Easily run and scale a model across your clusters.

27. So what we actually learned
(except from all the cool stuff we can add to our CVs)
* Decouple everything.
* When you start copying code and configs -> tools down and re-think of your applications setup.
* Try new technologies. The initial learning curve will compensate you later.
* Work tightly with data scientists so they develop similar mindset to an engineer.