merge: Move OpenTelemetry integration outside core modules (#81)

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

Although this worked as expected, the overhead of the OpenTelemetry when
collecting metrics during simulation was considerable and lacked more
optimization opportunities (other than providing a separate API
implementation). Furthermore, since we were tied to OpenTelemetry's SDK
implementation, we experienced issues with throttling and registering
multiple instruments.

We will instead use another approach, where we expose the core metrics
in OpenDC via specialized interfaces (see #80) such that
access is fast and can be done without having to interface with
OpenTelemetry. In addition, we will provide an adapter to that is able
to forward these metrics to OpenTelemetry implementations, so we can
still integrate with the wider ecosystem.

## Implementation Notes :hammer_and_pick:

* Remove OpenTelemetry from "compute" modules 
* Remove OpenTelemetry from "workflow" modules 
* Remove OpenTelemetry from "FaaS" modules
* Remove OpenTelemetry from TF20 experiment 
* Remove dependency on OpenTelemetry SDK 

## External Dependencies :four_leaf_clover:

* N/A

## Breaking API Changes :warning:

* Metrics are not anymore directly exposed via OpenTelemetry. Instead, an adapter needs to be used to access the data via OpenTelemetry.

2 files changed, 10 insertions, 78 deletions

diff --git a/opendc-workflow/opendc-workflow-workload/build.gradle.kts b/opendc-workflow/opendc-workflow-workload/build.gradle.kts
index b725a69c..17eadf29 100644
--- a/opendc-workflow/opendc-workflow-workload/build.gradle.kts
+++ b/opendc-workflow/opendc-workflow-workload/build.gradle.kts
@@ -32,6 +32,4 @@ dependencies {
 
     implementation(projects.opendcSimulator.opendcSimulatorCompute)
     implementation(projects.opendcTrace.opendcTraceApi)
-    implementation(projects.opendcTelemetry.opendcTelemetrySdk)
-    implementation(libs.opentelemetry.semconv)
 }
diff --git a/opendc-workflow/opendc-workflow-workload/src/main/kotlin/org/opendc/workflow/workload/WorkflowServiceHelper.kt b/opendc-workflow/opendc-workflow-workload/src/main/kotlin/org/opendc/workflow/workload/WorkflowServiceHelper.kt
index a7d0ed6c..435d0190 100644
--- a/opendc-workflow/opendc-workflow-workload/src/main/kotlin/org/opendc/workflow/workload/WorkflowServiceHelper.kt
+++ b/opendc-workflow/opendc-workflow-workload/src/main/kotlin/org/opendc/workflow/workload/WorkflowServiceHelper.kt
@@ -22,24 +22,13 @@
 
 package org.opendc.workflow.workload
 
-import io.opentelemetry.api.metrics.MeterProvider
-import io.opentelemetry.sdk.common.CompletableResultCode
-import io.opentelemetry.sdk.metrics.SdkMeterProvider
-import io.opentelemetry.sdk.metrics.data.AggregationTemporality
-import io.opentelemetry.sdk.metrics.export.MetricProducer
-import io.opentelemetry.sdk.metrics.export.MetricReader
-import io.opentelemetry.sdk.metrics.export.MetricReaderFactory
-import io.opentelemetry.sdk.resources.Resource
-import io.opentelemetry.semconv.resource.attributes.ResourceAttributes
 import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
 import org.opendc.compute.api.ComputeClient
-import org.opendc.telemetry.sdk.toOtelClock
 import org.opendc.workflow.api.Job
 import org.opendc.workflow.service.WorkflowService
 import java.time.Clock
-import java.util.*
 import kotlin.coroutines.CoroutineContext
 
 /**
@@ -59,60 +48,16 @@ public class WorkflowServiceHelper(
     /**
      * The [WorkflowService] that is constructed by this runner.
      */
-    public val service: WorkflowService
-
-    /**
-     * The [MetricProducer] exposed by the [WorkflowService].
-     */
-    public lateinit var metricProducer: MetricProducer
-        private set
-
-    /**
-     * The [MeterProvider] used for the service.
-     */
-    private val _meterProvider: SdkMeterProvider
-
-    /**
-     * The list of [MetricReader]s that have been registered with the runner.
-     */
-    private val _metricReaders = mutableListOf<MetricReader>()
-
-    init {
-        val resource = Resource.builder()
-            .put(ResourceAttributes.SERVICE_NAME, "opendc-workflow")
-            .build()
-
-        _meterProvider = SdkMeterProvider.builder()
-            .setClock(clock.toOtelClock())
-            .setResource(resource)
-            .registerMetricReader { producer ->
-                metricProducer = producer
-
-                val metricReaders = _metricReaders
-                object : MetricReader {
-                    override fun getPreferredTemporality(): AggregationTemporality = AggregationTemporality.CUMULATIVE
-                    override fun flush(): CompletableResultCode {
-                        return CompletableResultCode.ofAll(metricReaders.map { it.flush() })
-                    }
-                    override fun shutdown(): CompletableResultCode {
-                        return CompletableResultCode.ofAll(metricReaders.map { it.shutdown() })
-                    }
-                }
-            }
-            .build()
-
-        service = WorkflowService(
-            context,
-            clock,
-            _meterProvider,
-            computeClient,
-            schedulerSpec.schedulingQuantum,
-            jobAdmissionPolicy = schedulerSpec.jobAdmissionPolicy,
-            jobOrderPolicy = schedulerSpec.jobOrderPolicy,
-            taskEligibilityPolicy = schedulerSpec.taskEligibilityPolicy,
-            taskOrderPolicy = schedulerSpec.taskOrderPolicy,
-        )
-    }
+    public val service: WorkflowService = WorkflowService(
+        context,
+        clock,
+        computeClient,
+        schedulerSpec.schedulingQuantum,
+        jobAdmissionPolicy = schedulerSpec.jobAdmissionPolicy,
+        jobOrderPolicy = schedulerSpec.jobOrderPolicy,
+        taskEligibilityPolicy = schedulerSpec.taskEligibilityPolicy,
+        taskOrderPolicy = schedulerSpec.taskOrderPolicy,
+    )
 
     /**
      * Run the specified list of [jobs] using the workflow service and suspend execution until all jobs have
@@ -146,19 +91,8 @@ public class WorkflowServiceHelper(
         }
     }
 
-    /**
-     * Register a [MetricReader] for this helper.
-     *
-     * @param factory The factory for the reader to register.
-     */
-    public fun registerMetricReader(factory: MetricReaderFactory) {
-        val reader = factory.apply(metricProducer)
-        _metricReaders.add(reader)
-    }
-
     override fun close() {
         computeClient.close()
         service.close()
-        _meterProvider.close()
     }
 }