refactor(workflow/service): Remove OpenTelemetry from "FaaS" modules

This change removes the OpenTelemetry integration from the OpenDC
FaaS modules. Previously, we chose to integrate OpenTelemetry to
provide a unified way to report metrics to the users.

See the previous commit removing it from the "Compute" modules for the
reasoning behind this change.

3 files changed, 10 insertions, 133 deletions

diff --git a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt
index f7dc3c1f..7b40d867 100644
--- a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt
+++ b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt
@@ -22,8 +22,6 @@
 
 package org.opendc.faas.service
 
-import io.opentelemetry.api.metrics.Meter
-import io.opentelemetry.api.metrics.MeterProvider
 import org.opendc.faas.api.FaaSClient
 import org.opendc.faas.api.FaaSFunction
 import org.opendc.faas.service.autoscaler.FunctionTerminationPolicy
@@ -33,6 +31,7 @@ import org.opendc.faas.service.router.RoutingPolicy
 import org.opendc.faas.service.telemetry.FunctionStats
 import org.opendc.faas.service.telemetry.SchedulerStats
 import java.time.Clock
+import java.time.Duration
 import kotlin.coroutines.CoroutineContext
 
 /**
@@ -65,20 +64,20 @@ public interface FaaSService : AutoCloseable {
          *
          * @param context The [CoroutineContext] to use in the service.
          * @param clock The clock instance to use.
-         * @param meterProvider The [MeterProvider] to create a [Meter] with.
          * @param deployer the [FunctionDeployer] to use for deploying function instances.
          * @param routingPolicy The policy to route function invocations.
          * @param terminationPolicy The policy for terminating function instances.
+         * @param quantum The scheduling quantum of the service (100 ms default)
          */
         public operator fun invoke(
             context: CoroutineContext,
             clock: Clock,
-            meterProvider: MeterProvider,
             deployer: FunctionDeployer,
             routingPolicy: RoutingPolicy,
             terminationPolicy: FunctionTerminationPolicy,
+            quantum: Duration = Duration.ofMillis(100)
         ): FaaSService {
-            return FaaSServiceImpl(context, clock, meterProvider, deployer, routingPolicy, terminationPolicy)
+            return FaaSServiceImpl(context, clock, deployer, routingPolicy, terminationPolicy, quantum)
         }
     }
 }
diff --git a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FunctionObject.kt b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FunctionObject.kt
index 52fcffa1..1cc33f6f 100644
--- a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FunctionObject.kt
+++ b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FunctionObject.kt
@@ -22,13 +22,6 @@
 
 package org.opendc.faas.service
 
-import io.opentelemetry.api.common.AttributeKey
-import io.opentelemetry.api.common.Attributes
-import io.opentelemetry.api.metrics.LongCounter
-import io.opentelemetry.api.metrics.LongHistogram
-import io.opentelemetry.api.metrics.LongUpDownCounter
-import io.opentelemetry.api.metrics.Meter
-import io.opentelemetry.semconv.resource.attributes.ResourceAttributes
 import org.apache.commons.math3.stat.descriptive.DescriptiveStatistics
 import org.opendc.faas.service.deployer.FunctionInstance
 import org.opendc.faas.service.telemetry.FunctionStats
@@ -38,7 +31,6 @@ import java.util.*
  * An [FunctionObject] represents the service's view of a serverless function.
  */
 public class FunctionObject(
-    meter: Meter,
     public val uid: UUID,
     name: String,
     allocatedMemory: Long,
@@ -46,88 +38,16 @@ public class FunctionObject(
     meta: Map<String, Any>
 ) : AutoCloseable {
     /**
-     * The attributes of this function.
+     * Metrics tracked per function.
      */
-    private val attributes: Attributes = Attributes.builder()
-        .put(ResourceAttributes.FAAS_ID, uid.toString())
-        .put(ResourceAttributes.FAAS_NAME, name)
-        .put(ResourceAttributes.FAAS_MAX_MEMORY, allocatedMemory)
-        .put(AttributeKey.stringArrayKey("faas.labels"), labels.map { (k, v) -> "$k:$v" })
-        .build()
-
-    /**
-     * The total amount of function invocations received by the function.
-     */
-    private val invocations: LongCounter = meter.counterBuilder("function.invocations.total")
-        .setDescription("Number of function invocations")
-        .setUnit("1")
-        .build()
     private var _invocations = 0L
-
-    /**
-     * The amount of function invocations that could be handled directly.
-     */
-    private val timelyInvocations: LongCounter = meter.counterBuilder("function.invocations.warm")
-        .setDescription("Number of function invocations handled directly")
-        .setUnit("1")
-        .build()
     private var _timelyInvocations = 0L
-
-    /**
-     * The amount of function invocations that were delayed due to function deployment.
-     */
-    private val delayedInvocations: LongCounter = meter.counterBuilder("function.invocations.cold")
-        .setDescription("Number of function invocations that are delayed")
-        .setUnit("1")
-        .build()
     private var _delayedInvocations = 0L
-
-    /**
-     * The amount of function invocations that failed.
-     */
-    private val failedInvocations: LongCounter = meter.counterBuilder("function.invocations.failed")
-        .setDescription("Number of function invocations that failed")
-        .setUnit("1")
-        .build()
     private var _failedInvocations = 0L
-
-    /**
-     * The amount of instances for this function.
-     */
-    private val activeInstances: LongUpDownCounter = meter.upDownCounterBuilder("function.instances.active")
-        .setDescription("Number of active function instances")
-        .setUnit("1")
-        .build()
     private var _activeInstances = 0
-
-    /**
-     * The amount of idle instances for this function.
-     */
-    private val idleInstances: LongUpDownCounter = meter.upDownCounterBuilder("function.instances.idle")
-        .setDescription("Number of idle function instances")
-        .setUnit("1")
-        .build()
     private var _idleInstances = 0
-
-    /**
-     * The time that the function waited.
-     */
-    private val waitTime: LongHistogram = meter.histogramBuilder("function.time.wait")
-        .ofLongs()
-        .setDescription("Time the function has to wait before being started")
-        .setUnit("ms")
-        .build()
     private val _waitTime = DescriptiveStatistics()
         .apply { windowSize = 100 }
-
-    /**
-     * The time that the function was running.
-     */
-    private val activeTime: LongHistogram = meter.histogramBuilder("function.time.active")
-        .ofLongs()
-        .setDescription("Time the function was running")
-        .setUnit("ms")
-        .build()
     private val _activeTime = DescriptiveStatistics()
         .apply { windowSize = 100 }
 
@@ -150,7 +70,6 @@ public class FunctionObject(
      * Report a scheduled invocation.
      */
     internal fun reportSubmission() {
-        invocations.add(1, attributes)
         _invocations++
     }
 
@@ -159,13 +78,9 @@ public class FunctionObject(
      */
     internal fun reportDeployment(isDelayed: Boolean) {
         if (isDelayed) {
-            delayedInvocations.add(1, attributes)
             _delayedInvocations++
-
-            idleInstances.add(1, attributes)
             _idleInstances++
         } else {
-            timelyInvocations.add(1, attributes)
             _timelyInvocations++
         }
     }
@@ -175,12 +90,9 @@ public class FunctionObject(
      */
     internal fun reportStart(start: Long, submitTime: Long) {
         val wait = start - submitTime
-        waitTime.record(wait, attributes)
         _waitTime.addValue(wait.toDouble())
 
-        idleInstances.add(-1, attributes)
         _idleInstances--
-        activeInstances.add(1, attributes)
         _activeInstances++
     }
 
@@ -188,7 +100,6 @@ public class FunctionObject(
      * Report the failure of a function invocation.
      */
     internal fun reportFailure() {
-        failedInvocations.add(1, attributes)
         _failedInvocations++
     }
 
@@ -196,11 +107,8 @@ public class FunctionObject(
      * Report the end of a function invocation.
      */
     internal fun reportEnd(duration: Long) {
-        activeTime.record(duration, attributes)
         _activeTime.addValue(duration.toDouble())
-        idleInstances.add(1, attributes)
         _idleInstances++
-        activeInstances.add(-1, attributes)
         _activeInstances--
     }
 
diff --git a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt
index ce3b2b98..4ee55dea 100644
--- a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt
+++ b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt
@@ -22,8 +22,6 @@
 
 package org.opendc.faas.service.internal
 
-import io.opentelemetry.api.metrics.Meter
-import io.opentelemetry.api.metrics.MeterProvider
 import kotlinx.coroutines.*
 import kotlinx.coroutines.intrinsics.startCoroutineCancellable
 import mu.KotlinLogging
@@ -42,6 +40,7 @@ import org.opendc.faas.service.telemetry.FunctionStats
 import org.opendc.faas.service.telemetry.SchedulerStats
 import java.lang.IllegalStateException
 import java.time.Clock
+import java.time.Duration
 import java.util.*
 import kotlin.coroutines.Continuation
 import kotlin.coroutines.CoroutineContext
@@ -57,10 +56,10 @@ import kotlin.coroutines.resumeWithException
 internal class FaaSServiceImpl(
     context: CoroutineContext,
     private val clock: Clock,
-    meterProvider: MeterProvider,
     private val deployer: FunctionDeployer,
     private val routingPolicy: RoutingPolicy,
-    private val terminationPolicy: FunctionTerminationPolicy
+    private val terminationPolicy: FunctionTerminationPolicy,
+    quantum: Duration
 ) : FaaSService, FunctionInstanceListener {
     /**
      * The [CoroutineScope] of the service bounded by the lifecycle of the service.
@@ -73,14 +72,9 @@ internal class FaaSServiceImpl(
     private val logger = KotlinLogging.logger {}
 
     /**
-     * The [Meter] that collects the metrics of this service.
-     */
-    private val meter = meterProvider.get("org.opendc.faas.service")
-
-    /**
      * The [Pacer] to use for scheduling the scheduler cycles.
      */
-    private val pacer = Pacer(scope.coroutineContext, clock, quantum = 100) { doSchedule() }
+    private val pacer = Pacer(scope.coroutineContext, clock, quantum = quantum.toMillis()) { doSchedule() }
 
     /**
      * The [Random] instance used to generate unique identifiers for the objects.
@@ -99,30 +93,10 @@ internal class FaaSServiceImpl(
     private val queue = ArrayDeque<InvocationRequest>()
 
     /**
-     * The total amount of function invocations received by the service.
+     * Metrics tracked by the service.
      */
-    private val _invocations = meter.counterBuilder("service.invocations.total")
-        .setDescription("Number of function invocations")
-        .setUnit("1")
-        .build()
     private var totalInvocations = 0L
-
-    /**
-     * The amount of function invocations that could be handled directly.
-     */
-    private val _timelyInvocations = meter.counterBuilder("service.invocations.warm")
-        .setDescription("Number of function invocations handled directly")
-        .setUnit("1")
-        .build()
     private var timelyInvocations = 0L
-
-    /**
-     * The amount of function invocations that were delayed due to function deployment.
-     */
-    private val _delayedInvocations = meter.counterBuilder("service.invocations.cold")
-        .setDescription("Number of function invocations that are delayed")
-        .setUnit("1")
-        .build()
     private var delayedInvocations = 0L
 
     override fun newClient(): FaaSClient {
@@ -165,7 +139,6 @@ internal class FaaSServiceImpl(
 
                 val uid = UUID(clock.millis(), random.nextLong())
                 val function = FunctionObject(
-                    meter,
                     uid,
                     name,
                     memorySize,
@@ -232,7 +205,6 @@ internal class FaaSServiceImpl(
                 }
 
                 val instance = if (activeInstance != null) {
-                    _timelyInvocations.add(1)
                     timelyInvocations++
                     function.reportDeployment(isDelayed = false)
 
@@ -242,7 +214,6 @@ internal class FaaSServiceImpl(
                     instances.add(instance)
                     terminationPolicy.enqueue(instance)
 
-                    _delayedInvocations.add(1)
                     delayedInvocations++
                     function.reportDeployment(isDelayed = true)
 
@@ -271,7 +242,6 @@ internal class FaaSServiceImpl(
     suspend fun invoke(function: FunctionObject) {
         check(function.uid in functions) { "Function does not exist (anymore)" }
 
-        _invocations.add(1)
         totalInvocations++
         function.reportSubmission()