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Initialization

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Tracker​

Assuming you have completed the Scala Tracker Setup, you are ready to initialize the Scala Tracker.

import scala.concurrent.ExecutionContext.Implicits.global

import com.snowplowanalytics.snowplow.scalatracker._
import com.snowplowanalytics.snowplow.scalatracker.emitters._

val emitter1 = AsyncEmitter.createAndStart("mycollector.com")
val emitter2 = new SyncEmitter("myothercollector.com", port = 8080)
val emitter3 = AsyncBatchEmitter.createAndStart(host = "myothercollector.com", port = 8080, bufferSize = 32)
val tracker = new Tracker(List(emitter1, emitter2, emitter3), "mytrackername", "myapplicationid")

The above code:

  • creates a non-blocking emitter, emitter1, with global execution context, which sends events to "mycollector.com" on the default port, port 80
  • creates a blocking emitter, emitter2, which sends events to "myothercollector.com" on port 8080
  • creates a non-blocking batch emitter3, with global execution context, which will buffer events until buffer size reach 32 events and then send all of them at once in POST request
  • creates a tracker which can be used to send events to all emitters

Subject​

You can configure a subject with extra data and attach it to the tracker so that the data will be attached to every event:

val subject = new Subject()
  .setUserId("user-00035")
  .setPlatform(Desktop)
tracker.setSubject(subject)

EC2 Context​

Amazon Elastic Cloud can provide basic information about instance running your app. You can add this informational as additional custom context to all sent events by enabling it in Tracker after initializaiton of your tracker:

tracker.enableEc2Context()

Google Compute Engine Metadata context​

Google Cloud Compute Engine can provide basic information about instance running your app. You can add this informational as additional custom context to all sent events by enabling it in Tracker after initializaiton of your tracker:

tracker.enableGceContext()

This will add iglu:com.google.cloud.gce/instance_metadata/jsonschema/1-0-0 context to all your events

Callbacks​

All emitters supplied with Scala Tracker support callbacks invoked after every sent event (or batch of events) whether it was successful or not. This feature particularly useful for checking collector unavailability and tracker debugging.

Callbacks should have following signature:

type Callback = (CollectorParams, CollectorRequest, CollectorResponse) => Unit
  • CollectorParams is collector configuration attached to emitter
  • CollectorRequest is raw collector's payload, which can be either GET or POST and holding number of undertaken attempts
  • CollectorResponse is processed collector's response or failure reason. You'll want to pattern-match it to either no-op or notify DevOps about non-working collector

To add a callback to AsyncBatchEmitter you can use following approach:

def emitterCallback(params: CollectorParams, req: CollectorRequest, res: CollectorResponse): Unit = {
  res match {
    case TEmitter.CollectorSuccess(_) => ()
    case TEmitter.CollectorFailure(code) => 
      devopsIncident(s"Scala Tracker got unexpected HTTP code $code from ${params.getUri}")
    case TEmitter.TrackerFailure(exception) => 
      devopsIncident(s"Scala Tracker failed to reach ${params.getUri} with following exception $exception after ${req.attempt} attempt")
    case TEmitter.RetriesExceeded(failure) =>
      devopsIncident(s"Scala Tracker has stopped trying to deliver payload after following failure: $failure")
      savePayload(req)      // can be investigated and sent afterwards
  }
}
val emitter = AsyncBatchEmitter.createAndStart(collector, port, bufferSize = 32, callback = Some(emitterCallback _))

All async emitters will perform callbacks asynchronously in their ExecutionContext.