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doors-exercise

Pre-requisites

Project is built using SBT >= 1

Flink cluster with Kafka is containerized so latest available Docker is needed as well.

To run

Run in Docker

Build and package the Flink job to a fat jar:

sbt assembly

Start docker-compose with Flink and Kafka:

docker-compose up -d

Get the id of Flink job manager container:

JOBMANAGER_CONTAINER=$(docker ps --filter name=flink-jobmanager --format={{.ID}})

Copy the jar to the container:

docker cp target/scala-2.12/doors-exercise-job.jar "$JOBMANAGER_CONTAINER":/job.jar

Run the job

docker exec -t -i "$JOBMANAGER_CONTAINER" flink run /job.jar

Check the execution in Flink UI :

http://localhost:8081/#/overview

Consult produced stats

To check produced stats in Kafka: docker exec -t -i $(docker ps --filter name=doors-kafka --format={{.ID}}) /opt/kafka/bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic doors-stats

Run the job in SBT

We still need to provide Kafka input/output topics for the job, to run Kafka only (without Flink containers):

docker-compose up -d -f docker-compose-only-kafka.yml up

Then to run and test your application locally, you can just execute sbt run then select the main class that contains the Flink job .

Door stream

We use event time as stream time characteristic

val env = StreamExecutionEnvironment.getExecutionEnvironment
env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime)

Domain

Main abstraction is a DoorEvent which looks like this:

final case class DoorEvent(doorId: Int, eventType: DoorEventType, timestamp: Long)

When events are persisted to Kafka topic they are serialized to Json format (see com.doors.utils.Json for details)

Doors stream input

Doors are generated and pushed to input Kafka topic doors which is used as input source for main streaming flow in DoorsJob.

I used the same job to generate the input source, in real-world scenario another job or producer would have been used.

Doors Generator

I use simple door generator which picks random door from 200 available and assigns random IN/OUT event and timestamp with random delay within a limit.

DoorEventSource function emits generated events in order (no late event processing in the main stream).

Kafka sink for generated doors

All door events are streamed to Kafka sink, to topic doors

Main door processing stream flow

reading events from Kafka

We basically try to deserialize Json events and filter out errors.

val doorsStream =
      env.addSource(source).name("Doors input stream")
        .map(toDoorEvent)
        .filter(_.isSuccess)
        .map(_.get)
        .assignAscendingTimestamps(_.timestamp)

Since events don't come out-of-order we can assign ascending timestamps and watermarks.

counting per door and producing basic stats

We group events by doorId field using tumbling window of 10 secs and preagregate counting types of event to :

final case class PerDoorCounts(doorId: String, count: Int, inCount: Int, outCount: Int)

  val countPerDoorStream = doorsStream
      .keyBy(_.doorId)
      .timeWindow(WINDOW_SIZE)
      .aggregate(new PerDoorAggregation)

then we can count simple stats per doors grouping all streams by window of 10 secs

    val allPerDoorCounts = countPerDoorStream.timeWindowAll(WINDOW_SIZE)
    
    // example of one of the stats
    allPerDoorCounts
      .maxBy("count")
      .map(counts => DoorStats[PerDoorCounts](StatsType.door_most_used, counts))
      .addSink(doorStatsSink)

output basic stats per door

Door stats are pushed to another Kafka topic doors-stats in Json format.

Basic door stats case class : `final case class DoorStats[T<:DoorStatsValue](key: StatsType, value: T)

compute total stats across all doors

We reuse aggregated stream with cound per door from previous steps:

val allPerDoorCounts = countPerDoorStream.timeWindowAll(WINDOW_SIZE)

then we need to aggregate events per period (window start-end) to be able to produce stats correspondig to this interface :

final case class TotalCounts(period: Period, count: Int)

using reduce function to inkect window infos:

allPerDoorCounts
      .reduce(
        (ev1: PerDoorCounts, ev2: PerDoorCounts) => ev1.copy(count = ev1.count + ev2.count),
        (
          window: TimeWindow,
          counts: Iterable[PerDoorCounts],
          out: Collector[TotalCounts]) => {
          out.collect(TotalCounts(Period(window.getStart, window.getEnd), counts.iterator.next().count))
        }
      )

with the result stream we can count min/max events across different windows. Using here sliding window of 1 minute compiuted every 10 secs:

// one stats as example
 .windowAll(SlidingEventTimeWindows.of(TOTAL_STATS_WINDOW_SIZE, TOTAL_STATS_WINDOW_SLIDE))
      .minBy("count")
      .map(counts => DoorStats[TotalCounts](StatsType.less_busy_window, counts))

output total stats

Stats are pushed to Kafka topic doors-stats in Json format.

TODO

  • UI push stats to Elastic Search + Kibana for visualization
  • CEP with door patterns