Integrate OpenTelemetry into OpenDC

This pull request resolves issue #91 by adopting the industry-standard OpenTelemetry standard
for collecting traces and metrics in OpenDC simulations:

* Metrics will now be exposed through OpenTelemetry's metrics API
* `opendc-telemetry` provides complementary code to support
    gathering telemetry in OpenDC.

**Breaking API Changes**
* `opendc-tracer` has been removed.
* `EventFlow` and all usages of it have been removed.
* `opendc-experiments-sc18` has been removed for now, but a 
    suitable replacement will follow soon.

7 files changed, 258 insertions, 275 deletions

diff --git a/simulator/opendc-workflow/opendc-workflow-service/build.gradle.kts b/simulator/opendc-workflow/opendc-workflow-service/build.gradle.kts
index bec18ae9..040a9ff6 100644
--- a/simulator/opendc-workflow/opendc-workflow-service/build.gradle.kts
+++ b/simulator/opendc-workflow/opendc-workflow-service/build.gradle.kts
@@ -33,13 +33,14 @@ dependencies {
     api(platform(project(":opendc-platform")))
     api(project(":opendc-workflow:opendc-workflow-api"))
     api(project(":opendc-compute:opendc-compute-api"))
-    api(project(":opendc-trace:opendc-trace-core"))
+    api(project(":opendc-telemetry:opendc-telemetry-api"))
     implementation(project(":opendc-utils"))
     implementation("io.github.microutils:kotlin-logging")
 
     testImplementation(project(":opendc-simulator:opendc-simulator-core"))
     testImplementation(project(":opendc-compute:opendc-compute-simulator"))
     testImplementation(project(":opendc-format"))
+    testImplementation(project(":opendc-telemetry:opendc-telemetry-sdk"))
     testImplementation("com.fasterxml.jackson.module:jackson-module-kotlin:${versions["jackson-module-kotlin"]}")
     testRuntimeOnly("org.apache.logging.log4j:log4j-slf4j-impl")
 }
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowEvent.kt b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowEvent.kt
deleted file mode 100644
index bb2ad6c6..00000000
--- a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowEvent.kt
+++ /dev/null
@@ -1,79 +0,0 @@
-/*
- * Copyright (c) 2021 AtLarge Research
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
- * SOFTWARE.
- */
-
-package org.opendc.workflow.service
-
-import org.opendc.trace.core.Event
-import org.opendc.workflow.api.Job
-import org.opendc.workflow.api.Task
-
-/**
- * An event emitted by the [WorkflowService].
- */
-public sealed class WorkflowEvent : Event() {
-    /**
-     * The [WorkflowService] that emitted the event.
-     */
-    public abstract val service: WorkflowService
-
-    /**
-     * This event is emitted when a job was submitted to the scheduler.
-     */
-    public data class JobSubmitted(
-        override val service: WorkflowService,
-        public val job: Job
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a job has become active.
-     */
-    public data class JobStarted(
-        override val service: WorkflowService,
-        public val job: Job
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a job has finished processing.
-     */
-    public data class JobFinished(
-        override val service: WorkflowService,
-        public val job: Job
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a task of a job has started processing.
-     */
-    public data class TaskStarted(
-        override val service: WorkflowService,
-        public val job: Job,
-        public val task: Task
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a task of a job has started processing.
-     */
-    public data class TaskFinished(
-        override val service: WorkflowService,
-        public val job: Job,
-        public val task: Task
-    ) : WorkflowEvent()
-}
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt
index 2f83e376..d3358ef1 100644
--- a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt
+++ b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt
@@ -22,9 +22,8 @@
 
 package org.opendc.workflow.service
 
-import kotlinx.coroutines.flow.Flow
+import io.opentelemetry.api.metrics.Meter
 import org.opendc.compute.api.ComputeClient
-import org.opendc.trace.core.EventTracer
 import org.opendc.workflow.api.Job
 import org.opendc.workflow.service.internal.WorkflowServiceImpl
 import org.opendc.workflow.service.scheduler.WorkflowSchedulerMode
@@ -42,14 +41,14 @@ import kotlin.coroutines.CoroutineContext
  */
 public interface WorkflowService : AutoCloseable {
     /**
-     * The events emitted by the workflow scheduler.
+     * Submit the specified [Job] to the workflow service for scheduling.
      */
-    public val events: Flow<WorkflowEvent>
+    public suspend fun submit(job: Job)
 
     /**
-     * Submit the specified [Job] to the workflow service for scheduling.
+     * Run the specified [Job] and suspend execution until the job is finished.
      */
-    public suspend fun submit(job: Job)
+    public suspend fun run(job: Job)
 
     /**
      * Terminate the lifecycle of the workflow service, stopping all running workflows.
@@ -63,6 +62,7 @@ public interface WorkflowService : AutoCloseable {
          * @param context The [CoroutineContext] to use in the service.
          * @param clock The clock instance to use.
          * @param tracer The event tracer to use.
+         * @param meter The meter to use.
          * @param compute The compute client to use.
          * @param mode The scheduling mode to use.
          * @param jobAdmissionPolicy The job admission policy to use.
@@ -73,7 +73,7 @@ public interface WorkflowService : AutoCloseable {
         public operator fun invoke(
             context: CoroutineContext,
             clock: Clock,
-            tracer: EventTracer,
+            meter: Meter,
             compute: ComputeClient,
             mode: WorkflowSchedulerMode,
             jobAdmissionPolicy: JobAdmissionPolicy,
@@ -84,7 +84,7 @@ public interface WorkflowService : AutoCloseable {
             return WorkflowServiceImpl(
                 context,
                 clock,
-                tracer,
+                meter,
                 compute,
                 mode,
                 jobAdmissionPolicy,
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
index 85a88acd..32191b8f 100644
--- a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
+++ b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
@@ -22,17 +22,11 @@
 
 package org.opendc.workflow.service.internal
 
-import kotlinx.coroutines.CoroutineScope
-import kotlinx.coroutines.ExperimentalCoroutinesApi
-import kotlinx.coroutines.cancel
-import kotlinx.coroutines.flow.Flow
+import io.opentelemetry.api.metrics.Meter
+import kotlinx.coroutines.*
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.launch
 import mu.KotlinLogging
 import org.opendc.compute.api.*
-import org.opendc.trace.core.EventTracer
-import org.opendc.trace.core.consumeAsFlow
-import org.opendc.trace.core.enable
 import org.opendc.workflow.api.Job
 import org.opendc.workflow.api.WORKFLOW_TASK_CORES
 import org.opendc.workflow.service.*
@@ -43,7 +37,9 @@ import org.opendc.workflow.service.scheduler.task.TaskEligibilityPolicy
 import org.opendc.workflow.service.scheduler.task.TaskOrderPolicy
 import java.time.Clock
 import java.util.*
+import kotlin.coroutines.Continuation
 import kotlin.coroutines.CoroutineContext
+import kotlin.coroutines.resume
 
 /**
  * A [WorkflowService] that distributes work through a multi-stage process based on the Reference Architecture for
@@ -52,7 +48,7 @@ import kotlin.coroutines.CoroutineContext
 public class WorkflowServiceImpl(
     context: CoroutineContext,
     internal val clock: Clock,
-    internal val tracer: EventTracer,
+    private val meter: Meter,
     private val computeClient: ComputeClient,
     mode: WorkflowSchedulerMode,
     jobAdmissionPolicy: JobAdmissionPolicy,
@@ -63,7 +59,7 @@ public class WorkflowServiceImpl(
     /**
      * The [CoroutineScope] of the service bounded by the lifecycle of the service.
      */
-    internal val scope = CoroutineScope(context)
+    internal val scope = CoroutineScope(context + Job())
 
     /**
      * The logger instance to use.
@@ -106,6 +102,11 @@ public class WorkflowServiceImpl(
     internal val taskByServer = mutableMapOf<Server, TaskState>()
 
     /**
+     * The continuation of the jobs.
+     */
+    private val conts = mutableMapOf<Job, Continuation<Unit>>()
+
+    /**
      * The root listener of this scheduler.
      */
     private val rootListener = object : WorkflowSchedulerListener {
@@ -151,6 +152,54 @@ public class WorkflowServiceImpl(
         }
     }
 
+    /**
+     * The number of jobs that have been submitted to the service.
+     */
+    private val submittedJobs = meter.longCounterBuilder("jobs.submitted")
+        .setDescription("Number of submitted jobs")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that are running.
+     */
+    private val runningJobs = meter.longUpDownCounterBuilder("jobs.active")
+        .setDescription("Number of jobs running")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that have finished running.
+     */
+    private val finishedJobs = meter.longCounterBuilder("jobs.finished")
+        .setDescription("Number of jobs that finished running")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of tasks that have been submitted to the service.
+     */
+    private val submittedTasks = meter.longCounterBuilder("tasks.submitted")
+        .setDescription("Number of submitted tasks")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that are running.
+     */
+    private val runningTasks = meter.longUpDownCounterBuilder("tasks.active")
+        .setDescription("Number of tasks running")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that have finished running.
+     */
+    private val finishedTasks = meter.longCounterBuilder("tasks.finished")
+        .setDescription("Number of tasks that finished running")
+        .setUnit("1")
+        .build()
+
     private val mode: WorkflowSchedulerMode.Logic
     private val jobAdmissionPolicy: JobAdmissionPolicy.Logic
     private val taskEligibilityPolicy: TaskEligibilityPolicy.Logic
@@ -167,16 +216,7 @@ public class WorkflowServiceImpl(
         }
     }
 
-    override val events: Flow<WorkflowEvent> = tracer.openRecording().let {
-        it.enable<WorkflowEvent.JobSubmitted>()
-        it.enable<WorkflowEvent.JobStarted>()
-        it.enable<WorkflowEvent.JobFinished>()
-        it.enable<WorkflowEvent.TaskStarted>()
-        it.enable<WorkflowEvent.TaskFinished>()
-        it.consumeAsFlow().map { event -> event as WorkflowEvent }
-    }
-
-    override suspend fun submit(job: Job) {
+    override suspend fun run(job: Job) {
         // J1 Incoming Jobs
         val jobInstance = JobState(job, clock.millis())
         val instances = job.tasks.associateWith {
@@ -193,14 +233,24 @@ public class WorkflowServiceImpl(
             if (instance.isRoot) {
                 instance.state = TaskStatus.READY
             }
+
+            submittedTasks.add(1)
         }
 
-        instances.values.toCollection(jobInstance.tasks)
-        incomingJobs += jobInstance
-        rootListener.jobSubmitted(jobInstance)
-        tracer.commit(WorkflowEvent.JobSubmitted(this, jobInstance.job))
+        return suspendCancellableCoroutine { cont ->
+            instances.values.toCollection(jobInstance.tasks)
+            incomingJobs += jobInstance
+            rootListener.jobSubmitted(jobInstance)
+            conts[job] = cont
+
+            submittedJobs.add(1)
+
+            requestCycle()
+        }
+    }
 
-        requestCycle()
+    override suspend fun submit(job: Job) {
+        scope.launch { run(job) }
     }
 
     override fun close() {
@@ -231,12 +281,8 @@ public class WorkflowServiceImpl(
             iterator.remove()
             jobQueue.add(jobInstance)
             activeJobs += jobInstance
-            tracer.commit(
-                WorkflowEvent.JobStarted(
-                    this,
-                    jobInstance.job
-                )
-            )
+
+            runningJobs.add(1)
             rootListener.jobStarted(jobInstance)
         }
 
@@ -311,18 +357,11 @@ public class WorkflowServiceImpl(
 
     public override fun onStateChanged(server: Server, newState: ServerState) {
         when (newState) {
-            ServerState.PROVISIONING -> {
-            }
+            ServerState.PROVISIONING -> {}
             ServerState.RUNNING -> {
                 val task = taskByServer.getValue(server)
                 task.startedAt = clock.millis()
-                tracer.commit(
-                    WorkflowEvent.TaskStarted(
-                        this@WorkflowServiceImpl,
-                        task.job.job,
-                        task.task
-                    )
-                )
+                runningTasks.add(1)
                 rootListener.taskStarted(task)
             }
             ServerState.TERMINATED, ServerState.ERROR -> {
@@ -338,13 +377,9 @@ public class WorkflowServiceImpl(
                 task.finishedAt = clock.millis()
                 job.tasks.remove(task)
                 activeTasks -= task
-                tracer.commit(
-                    WorkflowEvent.TaskFinished(
-                        this@WorkflowServiceImpl,
-                        task.job.job,
-                        task.task
-                    )
-                )
+
+                runningTasks.add(-1)
+                finishedTasks.add(1)
                 rootListener.taskFinished(task)
 
                 // Add job roots to the scheduling queue
@@ -371,8 +406,11 @@ public class WorkflowServiceImpl(
 
     private fun finishJob(job: JobState) {
         activeJobs -= job
-        tracer.commit(WorkflowEvent.JobFinished(this, job.job))
+        runningJobs.add(-1)
+        finishedJobs.add(1)
         rootListener.jobFinished(job)
+
+        conts.remove(job.job)?.resume(Unit)
     }
 
     public fun addListener(listener: WorkflowSchedulerListener) {
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/test/kotlin/org/opendc/workflow/service/StageWorkflowSchedulerIntegrationTest.kt b/simulator/opendc-workflow/opendc-workflow-service/src/test/kotlin/org/opendc/workflow/service/StageWorkflowSchedulerIntegrationTest.kt
deleted file mode 100644
index 2161f5f2..00000000
--- a/simulator/opendc-workflow/opendc-workflow-service/src/test/kotlin/org/opendc/workflow/service/StageWorkflowSchedulerIntegrationTest.kt
+++ /dev/null
@@ -1,139 +0,0 @@
-/*
- * Copyright (c) 2021 AtLarge Research
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
- * SOFTWARE.
- */
-
-package org.opendc.workflow.service
-
-import kotlinx.coroutines.ExperimentalCoroutinesApi
-import kotlinx.coroutines.delay
-import kotlinx.coroutines.flow.collect
-import kotlinx.coroutines.flow.onEach
-import kotlinx.coroutines.launch
-import kotlinx.coroutines.test.TestCoroutineScope
-import org.junit.jupiter.api.Assertions.assertEquals
-import org.junit.jupiter.api.Assertions.assertNotEquals
-import org.junit.jupiter.api.DisplayName
-import org.junit.jupiter.api.Test
-import org.junit.jupiter.api.assertAll
-import org.opendc.compute.service.ComputeService
-import org.opendc.compute.service.scheduler.NumberOfActiveServersAllocationPolicy
-import org.opendc.compute.simulator.SimHost
-import org.opendc.format.environment.sc18.Sc18EnvironmentReader
-import org.opendc.format.trace.gwf.GwfTraceReader
-import org.opendc.simulator.compute.SimSpaceSharedHypervisorProvider
-import org.opendc.simulator.utils.DelayControllerClockAdapter
-import org.opendc.trace.core.EventTracer
-import org.opendc.workflow.service.internal.WorkflowServiceImpl
-import org.opendc.workflow.service.scheduler.WorkflowSchedulerMode
-import org.opendc.workflow.service.scheduler.job.NullJobAdmissionPolicy
-import org.opendc.workflow.service.scheduler.job.SubmissionTimeJobOrderPolicy
-import org.opendc.workflow.service.scheduler.task.NullTaskEligibilityPolicy
-import org.opendc.workflow.service.scheduler.task.SubmissionTimeTaskOrderPolicy
-import kotlin.math.max
-
-/**
- * Integration test suite for the [WorkflowServiceImpl].
- */
-@DisplayName("WorkflowServiceImpl")
-@OptIn(ExperimentalCoroutinesApi::class)
-internal class StageWorkflowSchedulerIntegrationTest {
-    /**
-     * A large integration test where we check whether all tasks in some trace are executed correctly.
-     */
-    @Test
-    fun testTrace() {
-        var jobsSubmitted = 0L
-        var jobsStarted = 0L
-        var jobsFinished = 0L
-        var tasksStarted = 0L
-        var tasksFinished = 0L
-
-        val testScope = TestCoroutineScope()
-        val clock = DelayControllerClockAdapter(testScope)
-        val tracer = EventTracer(clock)
-
-        val scheduler = let {
-            val hosts = Sc18EnvironmentReader(object {}.javaClass.getResourceAsStream("/environment.json"))
-                .use { it.read() }
-                .map { def ->
-                    SimHost(
-                        def.uid,
-                        def.name,
-                        def.model,
-                        def.meta,
-                        testScope.coroutineContext,
-                        clock,
-                        SimSpaceSharedHypervisorProvider()
-                    )
-                }
-
-            val compute = ComputeService(testScope.coroutineContext, clock, tracer, NumberOfActiveServersAllocationPolicy(), schedulingQuantum = 1000)
-
-            hosts.forEach { compute.addHost(it) }
-
-            WorkflowService(
-                testScope.coroutineContext,
-                clock,
-                tracer,
-                compute.newClient(),
-                mode = WorkflowSchedulerMode.Batch(100),
-                jobAdmissionPolicy = NullJobAdmissionPolicy,
-                jobOrderPolicy = SubmissionTimeJobOrderPolicy(),
-                taskEligibilityPolicy = NullTaskEligibilityPolicy,
-                taskOrderPolicy = SubmissionTimeTaskOrderPolicy(),
-            )
-        }
-
-        testScope.launch {
-            scheduler.events
-                .onEach { event ->
-                    when (event) {
-                        is WorkflowEvent.JobStarted -> jobsStarted++
-                        is WorkflowEvent.JobFinished -> jobsFinished++
-                        is WorkflowEvent.TaskStarted -> tasksStarted++
-                        is WorkflowEvent.TaskFinished -> tasksFinished++
-                    }
-                }
-                .collect()
-        }
-
-        testScope.launch {
-            val reader = GwfTraceReader(object {}.javaClass.getResourceAsStream("/trace.gwf"))
-
-            while (reader.hasNext()) {
-                val entry = reader.next()
-                jobsSubmitted++
-                delay(max(0, entry.start - clock.millis()))
-                scheduler.submit(entry.workload)
-            }
-        }
-
-        testScope.advanceUntilIdle()
-
-        assertAll(
-            { assertEquals(emptyList<Throwable>(), testScope.uncaughtExceptions) },
-            { assertNotEquals(0, jobsSubmitted, "No jobs submitted") },
-            { assertEquals(jobsSubmitted, jobsStarted, "Not all submitted jobs started") },
-            { assertEquals(jobsSubmitted, jobsFinished, "Not all started jobs finished") },
-            { assertEquals(tasksStarted, tasksFinished, "Not all started tasks finished") }
-        )
-    }
-}
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/test/kotlin/org/opendc/workflow/service/WorkflowServiceIntegrationTest.kt b/simulator/opendc-workflow/opendc-workflow-service/src/test/kotlin/org/opendc/workflow/service/WorkflowServiceIntegrationTest.kt
new file mode 100644
index 00000000..46c0d835
--- /dev/null
+++ b/simulator/opendc-workflow/opendc-workflow-service/src/test/kotlin/org/opendc/workflow/service/WorkflowServiceIntegrationTest.kt
@@ -0,0 +1,159 @@
+/*
+ * Copyright (c) 2021 AtLarge Research
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.opendc.workflow.service
+
+import io.opentelemetry.api.metrics.MeterProvider
+import io.opentelemetry.sdk.metrics.SdkMeterProvider
+import io.opentelemetry.sdk.metrics.export.MetricProducer
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.test.runBlockingTest
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertAll
+import org.opendc.compute.service.ComputeService
+import org.opendc.compute.service.scheduler.NumberOfActiveServersAllocationPolicy
+import org.opendc.compute.simulator.SimHost
+import org.opendc.format.environment.sc18.Sc18EnvironmentReader
+import org.opendc.format.trace.gwf.GwfTraceReader
+import org.opendc.simulator.compute.SimSpaceSharedHypervisorProvider
+import org.opendc.simulator.utils.DelayControllerClockAdapter
+import org.opendc.telemetry.sdk.toOtelClock
+import org.opendc.workflow.service.internal.WorkflowServiceImpl
+import org.opendc.workflow.service.scheduler.WorkflowSchedulerMode
+import org.opendc.workflow.service.scheduler.job.NullJobAdmissionPolicy
+import org.opendc.workflow.service.scheduler.job.SubmissionTimeJobOrderPolicy
+import org.opendc.workflow.service.scheduler.task.NullTaskEligibilityPolicy
+import org.opendc.workflow.service.scheduler.task.SubmissionTimeTaskOrderPolicy
+import kotlin.math.max
+
+/**
+ * Integration test suite for the [WorkflowServiceImpl].
+ */
+@DisplayName("WorkflowServiceImpl")
+@OptIn(ExperimentalCoroutinesApi::class)
+internal class WorkflowServiceIntegrationTest {
+    /**
+     * A large integration test where we check whether all tasks in some trace are executed correctly.
+     */
+    @Test
+    fun testTrace() = runBlockingTest {
+        val clock = DelayControllerClockAdapter(this)
+
+        val meterProvider: MeterProvider = SdkMeterProvider
+            .builder()
+            .setClock(clock.toOtelClock())
+            .build()
+
+        val hosts = Sc18EnvironmentReader(object {}.javaClass.getResourceAsStream("/environment.json"))
+            .use { it.read() }
+            .map { def ->
+                SimHost(
+                    def.uid,
+                    def.name,
+                    def.model,
+                    def.meta,
+                    coroutineContext,
+                    clock,
+                    MeterProvider.noop().get("opendc-compute-simulator"),
+                    SimSpaceSharedHypervisorProvider()
+                )
+            }
+
+        val meter = MeterProvider.noop().get("opendc-compute")
+        val compute = ComputeService(coroutineContext, clock, meter, NumberOfActiveServersAllocationPolicy(), schedulingQuantum = 1000)
+
+        hosts.forEach { compute.addHost(it) }
+
+        val scheduler = WorkflowService(
+            coroutineContext,
+            clock,
+            meterProvider.get("opendc-workflow"),
+            compute.newClient(),
+            mode = WorkflowSchedulerMode.Batch(100),
+            jobAdmissionPolicy = NullJobAdmissionPolicy,
+            jobOrderPolicy = SubmissionTimeJobOrderPolicy(),
+            taskEligibilityPolicy = NullTaskEligibilityPolicy,
+            taskOrderPolicy = SubmissionTimeTaskOrderPolicy(),
+        )
+
+        val reader = GwfTraceReader(object {}.javaClass.getResourceAsStream("/trace.gwf"))
+        var offset = Long.MIN_VALUE
+
+        coroutineScope {
+            while (reader.hasNext()) {
+                val entry = reader.next()
+
+                if (offset < 0) {
+                    offset = entry.start - clock.millis()
+                }
+
+                delay(max(0, (entry.start - offset) - clock.millis()))
+                launch {
+                    scheduler.run(entry.workload)
+                }
+            }
+        }
+
+        hosts.forEach(SimHost::close)
+        scheduler.close()
+        compute.close()
+
+        val metrics = collectMetrics(meterProvider as MetricProducer)
+
+        assertAll(
+            { assertEquals(758, metrics.jobsSubmitted, "No jobs submitted") },
+            { assertEquals(0, metrics.jobsActive, "Not all submitted jobs started") },
+            { assertEquals(metrics.jobsSubmitted, metrics.jobsFinished, "Not all started jobs finished") },
+            { assertEquals(0, metrics.tasksActive, "Not all started tasks finished") },
+            { assertEquals(metrics.tasksSubmitted, metrics.tasksFinished, "Not all started tasks finished") }
+        )
+    }
+
+    class WorkflowMetrics {
+        var jobsSubmitted = 0L
+        var jobsActive = 0L
+        var jobsFinished = 0L
+        var tasksSubmitted = 0L
+        var tasksActive = 0L
+        var tasksFinished = 0L
+    }
+
+    /**
+     * Collect the metrics of the workflow service.
+     */
+    private fun collectMetrics(metricProducer: MetricProducer): WorkflowMetrics {
+        val metrics = metricProducer.collectAllMetrics().associateBy { it.name }
+        val res = WorkflowMetrics()
+        res.jobsSubmitted = metrics["jobs.submitted"]?.longSumData?.points?.last()?.value ?: 0
+        res.jobsActive = metrics["jobs.active"]?.longSumData?.points?.last()?.value ?: 0
+        res.jobsFinished = metrics["jobs.finished"]?.longSumData?.points?.last()?.value ?: 0
+        res.tasksSubmitted = metrics["tasks.submitted"]?.longSumData?.points?.last()?.value ?: 0
+        res.tasksActive = metrics["tasks.active"]?.longSumData?.points?.last()?.value ?: 0
+        res.tasksFinished = metrics["tasks.finished"]?.longSumData?.points?.last()?.value ?: 0
+        return res
+    }
+}
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/test/resources/log4j2.xml b/simulator/opendc-workflow/opendc-workflow-service/src/test/resources/log4j2.xml
index 70a0eacc..edcf41ed 100644
--- a/simulator/opendc-workflow/opendc-workflow-service/src/test/resources/log4j2.xml
+++ b/simulator/opendc-workflow/opendc-workflow-service/src/test/resources/log4j2.xml
@@ -28,6 +28,9 @@
         </Console>
     </Appenders>
     <Loggers>
+        <Logger name="org.opendc.workflow" level="info" additivity="false">
+            <AppenderRef ref="Console"/>
+        </Logger>
         <Root level="warn">
             <AppenderRef ref="Console"/>
         </Root>