merge: Integrate v2.1 progress into public repository

This pull request integrates the changes planned for the v2.1 release of
OpenDC into the public Github repository in order to sync the progress
of both repositories.

17 files changed, 766 insertions, 200 deletions

diff --git a/opendc-compute/opendc-compute-service/build.gradle.kts b/opendc-compute/opendc-compute-service/build.gradle.kts
index e0e48b0f..33cafc45 100644
--- a/opendc-compute/opendc-compute-service/build.gradle.kts
+++ b/opendc-compute/opendc-compute-service/build.gradle.kts
@@ -35,6 +35,7 @@ dependencies {
     api(projects.opendcTelemetry.opendcTelemetryApi)
     implementation(projects.opendcUtils)
     implementation(libs.kotlin.logging)
+    implementation(libs.opentelemetry.semconv)
 
     testImplementation(projects.opendcSimulator.opendcSimulatorCore)
     testRuntimeOnly(libs.log4j.slf4j)
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt
index 1873eb99..2a1fbaa0 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt
@@ -23,11 +23,13 @@
 package org.opendc.compute.service
 
 import io.opentelemetry.api.metrics.Meter
+import io.opentelemetry.api.metrics.MeterProvider
 import org.opendc.compute.api.ComputeClient
 import org.opendc.compute.service.driver.Host
 import org.opendc.compute.service.internal.ComputeServiceImpl
 import org.opendc.compute.service.scheduler.ComputeScheduler
 import java.time.Clock
+import java.time.Duration
 import kotlin.coroutines.CoroutineContext
 
 /**
@@ -70,16 +72,18 @@ public interface ComputeService : AutoCloseable {
          *
          * @param context The [CoroutineContext] to use in the service.
          * @param clock The clock instance to use.
+         * @param meterProvider The [MeterProvider] for creating a [Meter] for the service.
          * @param scheduler The scheduler implementation to use.
+         * @param schedulingQuantum The interval between scheduling cycles.
          */
         public operator fun invoke(
             context: CoroutineContext,
             clock: Clock,
-            meter: Meter,
+            meterProvider: MeterProvider,
             scheduler: ComputeScheduler,
-            schedulingQuantum: Long = 300000,
+            schedulingQuantum: Duration = Duration.ofMinutes(5),
         ): ComputeService {
-            return ComputeServiceImpl(context, clock, meter, scheduler, schedulingQuantum)
+            return ComputeServiceImpl(context, clock, meterProvider, scheduler, schedulingQuantum)
         }
     }
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/HostModel.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/HostModel.kt
index 5632a55e..fc092a3f 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/HostModel.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/HostModel.kt
@@ -25,7 +25,7 @@ package org.opendc.compute.service.driver
 /**
  * Describes the static machine properties of the host.
  *
- * @property vcpuCount The number of logical processing cores available for this host.
+ * @property cpuCount The number of logical processing cores available for this host.
  * @property memorySize The amount of memory available for this host in MB.
  */
 public data class HostModel(public val cpuCount: Int, public val memorySize: Long)
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt
index 8af5f86e..57e70fcd 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt
@@ -22,7 +22,10 @@
 
 package org.opendc.compute.service.internal
 
+import io.opentelemetry.api.common.AttributeKey
+import io.opentelemetry.api.common.Attributes
 import io.opentelemetry.api.metrics.Meter
+import io.opentelemetry.api.metrics.MeterProvider
 import kotlinx.coroutines.*
 import mu.KotlinLogging
 import org.opendc.compute.api.*
@@ -33,6 +36,7 @@ import org.opendc.compute.service.driver.HostState
 import org.opendc.compute.service.scheduler.ComputeScheduler
 import org.opendc.utils.TimerScheduler
 import java.time.Clock
+import java.time.Duration
 import java.util.*
 import kotlin.coroutines.CoroutineContext
 import kotlin.math.max
@@ -40,15 +44,18 @@ import kotlin.math.max
 /**
  * Internal implementation of the OpenDC Compute service.
  *
- * @param context The [CoroutineContext] to use.
- * @param clock The clock instance to keep track of time.
+ * @param context The [CoroutineContext] to use in the service.
+ * @param clock The clock instance to use.
+ * @param meterProvider The [MeterProvider] for creating a [Meter] for the service.
+ * @param scheduler The scheduler implementation to use.
+ * @param schedulingQuantum The interval between scheduling cycles.
  */
 internal class ComputeServiceImpl(
     private val context: CoroutineContext,
     private val clock: Clock,
-    private val meter: Meter,
+    meterProvider: MeterProvider,
     private val scheduler: ComputeScheduler,
-    private val schedulingQuantum: Long
+    private val schedulingQuantum: Duration
 ) : ComputeService, HostListener {
     /**
      * The [CoroutineScope] of the service bounded by the lifecycle of the service.
@@ -61,6 +68,11 @@ internal class ComputeServiceImpl(
     private val logger = KotlinLogging.logger {}
 
     /**
+     * The [Meter] to track metrics of the [ComputeService].
+     */
+    private val meter = meterProvider.get("org.opendc.compute.service")
+
+    /**
      * The [Random] instance used to generate unique identifiers for the objects.
      */
     private val random = Random(0)
@@ -104,60 +116,37 @@ internal class ComputeServiceImpl(
     private var maxMemory = 0L
 
     /**
-     * The number of servers that have been submitted to the service for provisioning.
-     */
-    private val _submittedServers = meter.longCounterBuilder("servers.submitted")
-        .setDescription("Number of start requests")
-        .setUnit("1")
-        .build()
-
-    /**
-     * The number of servers that failed to be scheduled.
-     */
-    private val _unscheduledServers = meter.longCounterBuilder("servers.unscheduled")
-        .setDescription("Number of unscheduled servers")
-        .setUnit("1")
-        .build()
-
-    /**
-     * The number of servers that are waiting to be provisioned.
-     */
-    private val _waitingServers = meter.longUpDownCounterBuilder("servers.waiting")
-        .setDescription("Number of servers waiting to be provisioned")
-        .setUnit("1")
-        .build()
-
-    /**
-     * The number of servers that are waiting to be provisioned.
+     * The number of scheduling attempts.
      */
-    private val _runningServers = meter.longUpDownCounterBuilder("servers.active")
-        .setDescription("Number of servers currently running")
+    private val _schedulingAttempts = meter.counterBuilder("scheduler.attempts")
+        .setDescription("Number of scheduling attempts")
         .setUnit("1")
         .build()
+    private val _schedulingAttemptsSuccess = _schedulingAttempts
+        .bind(Attributes.of(AttributeKey.stringKey("result"), "success"))
+    private val _schedulingAttemptsFailure = _schedulingAttempts
+        .bind(Attributes.of(AttributeKey.stringKey("result"), "failure"))
+    private val _schedulingAttemptsError = _schedulingAttempts
+        .bind(Attributes.of(AttributeKey.stringKey("result"), "error"))
 
     /**
-     * The number of servers that have finished running.
+     * The response time of the service.
      */
-    private val _finishedServers = meter.longCounterBuilder("servers.finished")
-        .setDescription("Number of servers that finished running")
-        .setUnit("1")
+    private val _schedulingLatency = meter.histogramBuilder("scheduler.latency")
+        .setDescription("End to end latency for a server to be scheduled (in multiple attempts)")
+        .ofLongs()
+        .setUnit("ms")
         .build()
 
     /**
-     * The number of hosts registered at the compute service.
+     * The number of servers that are pending.
      */
-    private val _hostCount = meter.longUpDownCounterBuilder("hosts.total")
-        .setDescription("Number of hosts")
-        .setUnit("1")
-        .build()
-
-    /**
-     * The number of available hosts registered at the compute service.
-     */
-    private val _availableHostCount = meter.longUpDownCounterBuilder("hosts.available")
-        .setDescription("Number of available hosts")
+    private val _servers = meter.upDownCounterBuilder("scheduler.servers")
+        .setDescription("Number of servers managed by the scheduler")
         .setUnit("1")
         .build()
+    private val _serversPending = _servers.bind(Attributes.of(AttributeKey.stringKey("state"), "pending"))
+    private val _serversActive = _servers.bind(Attributes.of(AttributeKey.stringKey("state"), "active"))
 
     /**
      * The [TimerScheduler] to use for scheduling the scheduler cycles.
@@ -170,6 +159,22 @@ internal class ComputeServiceImpl(
     override val hostCount: Int
         get() = hostToView.size
 
+    init {
+        val upState = Attributes.of(AttributeKey.stringKey("state"), "up")
+        val downState = Attributes.of(AttributeKey.stringKey("state"), "down")
+
+        meter.upDownCounterBuilder("scheduler.hosts")
+            .setDescription("Number of hosts registered with the scheduler")
+            .setUnit("1")
+            .buildWithCallback { result ->
+                val total = hostCount
+                val available = availableHosts.size.toLong()
+
+                result.observe(available, upState)
+                result.observe(total - available, downState)
+            }
+    }
+
     override fun newClient(): ComputeClient {
         check(scope.isActive) { "Service is already closed" }
         return object : ComputeClient {
@@ -297,24 +302,19 @@ internal class ComputeServiceImpl(
         hostToView[host] = hv
 
         if (host.state == HostState.UP) {
-            _availableHostCount.add(1)
             availableHosts += hv
         }
 
         scheduler.addHost(hv)
-        _hostCount.add(1)
         host.addListener(this)
     }
 
     override fun removeHost(host: Host) {
         val view = hostToView.remove(host)
         if (view != null) {
-            if (availableHosts.remove(view)) {
-                _availableHostCount.add(-1)
-            }
+            availableHosts.remove(view)
             scheduler.removeHost(view)
             host.removeListener(this)
-            _hostCount.add(-1)
         }
     }
 
@@ -325,10 +325,9 @@ internal class ComputeServiceImpl(
     internal fun schedule(server: InternalServer): SchedulingRequest {
         logger.debug { "Enqueueing server ${server.uid} to be assigned to host." }
 
-        val request = SchedulingRequest(server)
+        val request = SchedulingRequest(server, clock.millis())
         queue.add(request)
-        _submittedServers.add(1)
-        _waitingServers.add(1)
+        _serversPending.add(1)
         requestSchedulingCycle()
         return request
     }
@@ -354,10 +353,12 @@ internal class ComputeServiceImpl(
             return
         }
 
+        val quantum = schedulingQuantum.toMillis()
+
         // We assume that the provisioner runs at a fixed slot every time quantum (e.g t=0, t=60, t=120).
         // This is important because the slices of the VMs need to be aligned.
         // We calculate here the delay until the next scheduling slot.
-        val delay = schedulingQuantum - (clock.millis() % schedulingQuantum)
+        val delay = quantum - (clock.millis() % quantum)
 
         timerScheduler.startSingleTimer(Unit, delay) {
             doSchedule()
@@ -368,12 +369,13 @@ internal class ComputeServiceImpl(
      * Run a single scheduling iteration.
      */
     private fun doSchedule() {
+        val now = clock.millis()
         while (queue.isNotEmpty()) {
             val request = queue.peek()
 
             if (request.isCancelled) {
                 queue.poll()
-                _waitingServers.add(-1)
+                _serversPending.add(-1)
                 continue
             }
 
@@ -385,12 +387,12 @@ internal class ComputeServiceImpl(
                 if (server.flavor.memorySize > maxMemory || server.flavor.cpuCount > maxCores) {
                     // Remove the incoming image
                     queue.poll()
-                    _waitingServers.add(-1)
-                    _unscheduledServers.add(1)
+                    _serversPending.add(-1)
+                    _schedulingAttemptsFailure.add(1)
 
-                    logger.warn("Failed to spawn $server: does not fit [${clock.millis()}]")
+                    logger.warn { "Failed to spawn $server: does not fit [${clock.instant()}]" }
 
-                    server.state = ServerState.ERROR
+                    server.state = ServerState.TERMINATED
                     continue
                 } else {
                     break
@@ -401,7 +403,8 @@ internal class ComputeServiceImpl(
 
             // Remove request from queue
             queue.poll()
-            _waitingServers.add(-1)
+            _serversPending.add(-1)
+            _schedulingLatency.record(now - request.submitTime, server.attributes)
 
             logger.info { "Assigned server $server to host $host." }
 
@@ -416,12 +419,17 @@ internal class ComputeServiceImpl(
                     server.host = host
                     host.spawn(server)
                     activeServers[server] = host
+
+                    _serversActive.add(1)
+                    _schedulingAttemptsSuccess.add(1)
                 } catch (e: Throwable) {
-                    logger.error("Failed to deploy VM", e)
+                    logger.error(e) { "Failed to deploy VM" }
 
                     hv.instanceCount--
                     hv.provisionedCores -= server.flavor.cpuCount
                     hv.availableMemory += server.flavor.memorySize
+
+                    _schedulingAttemptsError.add(1)
                 }
             }
         }
@@ -430,7 +438,7 @@ internal class ComputeServiceImpl(
     /**
      * A request to schedule an [InternalServer] onto one of the [Host]s.
      */
-    internal data class SchedulingRequest(val server: InternalServer) {
+    internal data class SchedulingRequest(val server: InternalServer, val submitTime: Long) {
         /**
          * A flag to indicate that the request is cancelled.
          */
@@ -440,24 +448,22 @@ internal class ComputeServiceImpl(
     override fun onStateChanged(host: Host, newState: HostState) {
         when (newState) {
             HostState.UP -> {
-                logger.debug { "[${clock.millis()}] Host ${host.uid} state changed: $newState" }
+                logger.debug { "[${clock.instant()}] Host ${host.uid} state changed: $newState" }
 
                 val hv = hostToView[host]
                 if (hv != null) {
                     // Corner case for when the hypervisor already exists
                     availableHosts += hv
-                    _availableHostCount.add(1)
                 }
 
                 // Re-schedule on the new machine
                 requestSchedulingCycle()
             }
             HostState.DOWN -> {
-                logger.debug { "[${clock.millis()}] Host ${host.uid} state changed: $newState" }
+                logger.debug { "[${clock.instant()}] Host ${host.uid} state changed: $newState" }
 
                 val hv = hostToView[host] ?: return
                 availableHosts -= hv
-                _availableHostCount.add(-1)
 
                 requestSchedulingCycle()
             }
@@ -475,14 +481,12 @@ internal class ComputeServiceImpl(
 
         server.state = newState
 
-        if (newState == ServerState.RUNNING) {
-            _runningServers.add(1)
-        } else if (newState == ServerState.TERMINATED || newState == ServerState.DELETED) {
-            logger.info { "[${clock.millis()}] Server ${server.uid} ${server.name} ${server.flavor} finished." }
+        if (newState == ServerState.TERMINATED || newState == ServerState.DELETED) {
+            logger.info { "[${clock.instant()}] Server ${server.uid} ${server.name} ${server.flavor} finished." }
 
-            activeServers -= server
-            _runningServers.add(-1)
-            _finishedServers.add(1)
+            if (activeServers.remove(server) != null) {
+                _serversActive.add(-1)
+            }
 
             val hv = hostToView[host]
             if (hv != null) {
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/InternalServer.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/InternalServer.kt
index d9d0f3fc..05a7e1bf 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/InternalServer.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/InternalServer.kt
@@ -22,6 +22,9 @@
 
 package org.opendc.compute.service.internal
 
+import io.opentelemetry.api.common.AttributeKey
+import io.opentelemetry.api.common.Attributes
+import io.opentelemetry.semconv.resource.attributes.ResourceAttributes
 import mu.KotlinLogging
 import org.opendc.compute.api.*
 import org.opendc.compute.service.driver.Host
@@ -50,6 +53,21 @@ internal class InternalServer(
     private val watchers = mutableListOf<ServerWatcher>()
 
     /**
+     * The attributes of a server.
+     */
+    internal val attributes: Attributes = Attributes.builder()
+        .put(ResourceAttributes.HOST_NAME, name)
+        .put(ResourceAttributes.HOST_ID, uid.toString())
+        .put(ResourceAttributes.HOST_TYPE, flavor.name)
+        .put(AttributeKey.longKey("host.num_cpus"), flavor.cpuCount.toLong())
+        .put(AttributeKey.longKey("host.mem_capacity"), flavor.memorySize)
+        .put(AttributeKey.stringArrayKey("host.labels"), labels.map { (k, v) -> "$k:$v" })
+        .put(ResourceAttributes.HOST_ARCH, ResourceAttributes.HostArchValues.AMD64)
+        .put(ResourceAttributes.HOST_IMAGE_NAME, image.name)
+        .put(ResourceAttributes.HOST_IMAGE_ID, image.uid.toString())
+        .build()
+
+    /**
      * The [Host] that has been assigned to host the server.
      */
     internal var host: Host? = null
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt
index 0fd5b2a4..8c2d4715 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt
@@ -26,6 +26,8 @@ import org.opendc.compute.api.Server
 import org.opendc.compute.service.internal.HostView
 import org.opendc.compute.service.scheduler.filters.HostFilter
 import org.opendc.compute.service.scheduler.weights.HostWeigher
+import java.util.*
+import kotlin.math.min
 
 /**
  * A [ComputeScheduler] implementation that uses filtering and weighing passes to select
@@ -33,13 +35,27 @@ import org.opendc.compute.service.scheduler.weights.HostWeigher
  *
  * This implementation is based on the filter scheduler from OpenStack Nova.
  * See: https://docs.openstack.org/nova/latest/user/filter-scheduler.html
+ *
+ * @param filters The list of filters to apply when searching for an appropriate host.
+ * @param weighers The list of weighers to apply when searching for an appropriate host.
+ * @param subsetSize The size of the subset of best hosts from which a target is randomly chosen.
+ * @param random A [Random] instance for selecting
  */
-public class FilterScheduler(private val filters: List<HostFilter>, private val weighers: List<Pair<HostWeigher, Double>>) : ComputeScheduler {
+public class FilterScheduler(
+    private val filters: List<HostFilter>,
+    private val weighers: List<HostWeigher>,
+    private val subsetSize: Int = 1,
+    private val random: Random = Random(0)
+) : ComputeScheduler {
     /**
      * The pool of hosts available to the scheduler.
      */
     private val hosts = mutableListOf<HostView>()
 
+    init {
+        require(subsetSize >= 1) { "Subset size must be one or greater" }
+    }
+
     override fun addHost(host: HostView) {
         hosts.add(host)
     }
@@ -49,18 +65,44 @@ public class FilterScheduler(private val filters: List<HostFilter>, private val
     }
 
     override fun select(server: Server): HostView? {
-        return hosts.asSequence()
-            .filter { host ->
-                for (filter in filters) {
-                    if (!filter.test(host, server))
-                        return@filter false
+        val hosts = hosts
+        val filteredHosts = hosts.filter { host -> filters.all { filter -> filter.test(host, server) } }
+
+        val subset = if (weighers.isNotEmpty()) {
+            val results = weighers.map { it.getWeights(filteredHosts, server) }
+            val weights = DoubleArray(filteredHosts.size)
+
+            for (result in results) {
+                val min = result.min
+                val range = (result.max - min)
+
+                // Skip result if all weights are the same
+                if (range == 0.0) {
+                    continue
                 }
 
-                true
-            }
-            .sortedByDescending { host ->
-                weighers.sumByDouble { (weigher, factor) -> weigher.getWeight(host, server) * factor }
+                val multiplier = result.multiplier
+                val factor = multiplier / range
+
+                for ((i, weight) in result.weights.withIndex()) {
+                    weights[i] += factor * (weight - min)
+                }
             }
-            .firstOrNull()
+
+            weights.indices
+                .asSequence()
+                .sortedByDescending { weights[it] }
+                .map { filteredHosts[it] }
+                .take(subsetSize)
+                .toList()
+        } else {
+            filteredHosts
+        }
+
+        return when (val maxSize = min(subsetSize, subset.size)) {
+            0 -> null
+            1 -> subset[0]
+            else -> subset[random.nextInt(maxSize)]
+        }
     }
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/RamFilter.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/RamFilter.kt
new file mode 100644
index 00000000..a470a453
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/RamFilter.kt
@@ -0,0 +1,50 @@
+/*
+ * 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.compute.service.scheduler.filters
+
+import org.opendc.compute.api.Server
+import org.opendc.compute.service.internal.HostView
+
+/**
+ * A [HostFilter] that filters hosts based on the memory requirements of a [Server] and the RAM available on the host.
+ *
+ * @param allocationRatio Virtual RAM to physical RAM allocation ratio.
+ */
+public class RamFilter(private val allocationRatio: Double) : HostFilter {
+    override fun test(host: HostView, server: Server): Boolean {
+        val requested = server.flavor.memorySize
+        val available = host.availableMemory
+        val total = host.host.model.memorySize
+
+        // Do not allow an instance to overcommit against itself, only against
+        // other instances.
+        if (requested > total) {
+            return false
+        }
+
+        val limit = total * allocationRatio
+        val used = total - available
+        val usable = limit - used
+        return usable >= requested
+    }
+}
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/ComputeCapabilitiesFilter.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/VCpuFilter.kt
index 072440c5..abdd79f1 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/ComputeCapabilitiesFilter.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/VCpuFilter.kt
@@ -26,15 +26,22 @@ import org.opendc.compute.api.Server
 import org.opendc.compute.service.internal.HostView
 
 /**
- * A [HostFilter] that checks whether the capabilities provided by the host satisfies the requirements of the server
- * flavor.
+ * A [HostFilter] that filters hosts based on the vCPU requirements of a [Server] and the available vCPUs on the host.
+ *
+ * @param allocationRatio Virtual CPU to physical CPU allocation ratio.
  */
-public class ComputeCapabilitiesFilter : HostFilter {
+public class VCpuFilter(private val allocationRatio: Double) : HostFilter {
     override fun test(host: HostView, server: Server): Boolean {
-        val fitsMemory = host.availableMemory >= server.flavor.memorySize
-        val fitsCpu = host.host.model.cpuCount >= server.flavor.cpuCount
-        return fitsMemory && fitsCpu
-    }
+        val requested = server.flavor.cpuCount
+        val total = host.host.model.cpuCount
+        val limit = total * allocationRatio
 
-    override fun toString(): String = "ComputeCapabilitiesFilter"
+        // Do not allow an instance to overcommit against itself, only against other instances
+        if (requested > total) {
+            return false
+        }
+
+        val free = limit - host.provisionedCores
+        return free >= requested
+    }
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/CoreMemoryWeigher.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/CoreRamWeigher.kt
index 12e6510e..d668fdaf 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/CoreMemoryWeigher.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/CoreRamWeigher.kt
@@ -27,11 +27,15 @@ import org.opendc.compute.service.internal.HostView
 
 /**
  * A [HostWeigher] that weighs the hosts based on the available memory per core on the host.
+ *
+ * @param multiplier Weight multiplier ratio. A positive value will result in the scheduler preferring hosts with more
+ * available core memory, and a negative number will result in the scheduler preferring hosts with less available core
+ * memory.
  */
-public class CoreMemoryWeigher : HostWeigher {
+public class CoreRamWeigher(override val multiplier: Double = 1.0) : HostWeigher {
     override fun getWeight(host: HostView, server: Server): Double {
         return host.availableMemory.toDouble() / host.host.model.cpuCount
     }
 
-    override fun toString(): String = "CoreMemoryWeigher"
+    override fun toString(): String = "CoreRamWeigher"
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/HostWeigher.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/HostWeigher.kt
index d48ee9e0..aca8c4e6 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/HostWeigher.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/HostWeigher.kt
@@ -29,9 +29,47 @@ import org.opendc.compute.service.scheduler.FilterScheduler
 /**
  * An interface used by the [FilterScheduler] to weigh the pool of host for a scheduling request.
  */
-public fun interface HostWeigher {
+public interface HostWeigher {
+    /**
+     * The multiplier for the weigher.
+     */
+    public val multiplier: Double
+
     /**
      * Obtain the weight of the specified [host] when scheduling the specified [server].
      */
     public fun getWeight(host: HostView, server: Server): Double
+
+    /**
+     * Obtain the weights for [hosts] when scheduling the specified [server].
+     */
+    public fun getWeights(hosts: List<HostView>, server: Server): Result {
+        val weights = DoubleArray(hosts.size)
+        var min = Double.MAX_VALUE
+        var max = Double.MIN_VALUE
+
+        for ((i, host) in hosts.withIndex()) {
+            val weight = getWeight(host, server)
+            weights[i] = weight
+            min = kotlin.math.min(min, weight)
+            max = kotlin.math.max(max, weight)
+        }
+
+        return Result(weights, min, max, multiplier)
+    }
+
+    /**
+     * A result returned by the weigher.
+     *
+     * @param weights The weights returned by the weigher.
+     * @param min The minimum weight returned.
+     * @param max The maximum weight returned.
+     * @param multiplier The weight multiplier to use.
+     */
+    public class Result(
+        public val weights: DoubleArray,
+        public val min: Double,
+        public val max: Double,
+        public val multiplier: Double,
+    )
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/InstanceCountWeigher.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/InstanceCountWeigher.kt
index 2ef733e5..732cbe03 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/InstanceCountWeigher.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/InstanceCountWeigher.kt
@@ -28,7 +28,7 @@ import org.opendc.compute.service.internal.HostView
 /**
  * A [HostWeigher] that weighs the hosts based on the number of instances on the host.
  */
-public class InstanceCountWeigher : HostWeigher {
+public class InstanceCountWeigher(override val multiplier: Double = 1.0) : HostWeigher {
     override fun getWeight(host: HostView, server: Server): Double {
         return host.instanceCount.toDouble()
     }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/MemoryWeigher.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/RamWeigher.kt
index 115d8e4d..d18d31f4 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/MemoryWeigher.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/RamWeigher.kt
@@ -26,12 +26,15 @@ import org.opendc.compute.api.Server
 import org.opendc.compute.service.internal.HostView
 
 /**
- * A [HostWeigher] that weighs the hosts based on the available memory on the host.
+ * A [HostWeigher] that weighs the hosts based on the available RAM (memory) on the host.
+ *
+ * @param multiplier Weight multiplier ratio. A positive value will result in the scheduler preferring hosts with more
+ * available memory, and a negative number will result in the scheduler preferring hosts with less memory.
  */
-public class MemoryWeigher : HostWeigher {
+public class RamWeigher(override val multiplier: Double = 1.0) : HostWeigher {
     override fun getWeight(host: HostView, server: Server): Double {
         return host.availableMemory.toDouble()
     }
 
-    override fun toString(): String = "MemoryWeigher"
+    override fun toString(): String = "RamWeigher"
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/RandomWeigher.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/RandomWeigher.kt
deleted file mode 100644
index 1615df3a..00000000
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/RandomWeigher.kt
+++ /dev/null
@@ -1,36 +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.compute.service.scheduler.weights
-
-import org.opendc.compute.api.Server
-import org.opendc.compute.service.internal.HostView
-import java.util.*
-
-/**
- * A [HostWeigher] that assigns random weights to each host every selection.
- */
-public class RandomWeigher(private val random: Random) : HostWeigher {
-    override fun getWeight(host: HostView, server: Server): Double = random.nextDouble()
-
-    override fun toString(): String = "RandomWeigher"
-}
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/ProvisionedCoresWeigher.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/VCpuWeigher.kt
index df5bcd6e..4a22269b 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/ProvisionedCoresWeigher.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/weights/VCpuWeigher.kt
@@ -26,12 +26,19 @@ import org.opendc.compute.api.Server
 import org.opendc.compute.service.internal.HostView
 
 /**
- * A [HostWeigher] that weighs the hosts based on the number of provisioned cores on the host.
+ * A [HostWeigher] that weighs the hosts based on the remaining number of vCPUs available.
+ *
+ * @param allocationRatio Virtual CPU to physical CPU allocation ratio.
  */
-public class ProvisionedCoresWeigher : HostWeigher {
+public class VCpuWeigher(private val allocationRatio: Double, override val multiplier: Double = 1.0) : HostWeigher {
+
+    init {
+        require(allocationRatio > 0.0) { "Allocation ratio must be greater than zero" }
+    }
+
     override fun getWeight(host: HostView, server: Server): Double {
-        return host.provisionedCores.toDouble()
+        return host.host.model.cpuCount * allocationRatio - host.provisionedCores
     }
 
-    override fun toString(): String = "ProvisionedCoresWeigher"
+    override fun toString(): String = "VCpuWeigher"
 }
diff --git a/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt
index a6258845..564f9493 100644
--- a/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt
+++ b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt
@@ -37,9 +37,10 @@ import org.opendc.compute.service.driver.HostListener
 import org.opendc.compute.service.driver.HostModel
 import org.opendc.compute.service.driver.HostState
 import org.opendc.compute.service.scheduler.FilterScheduler
-import org.opendc.compute.service.scheduler.filters.ComputeCapabilitiesFilter
 import org.opendc.compute.service.scheduler.filters.ComputeFilter
-import org.opendc.compute.service.scheduler.weights.MemoryWeigher
+import org.opendc.compute.service.scheduler.filters.RamFilter
+import org.opendc.compute.service.scheduler.filters.VCpuFilter
+import org.opendc.compute.service.scheduler.weights.RamWeigher
 import org.opendc.simulator.core.SimulationCoroutineScope
 import org.opendc.simulator.core.runBlockingSimulation
 import java.util.*
@@ -57,11 +58,10 @@ internal class ComputeServiceTest {
         scope = SimulationCoroutineScope()
         val clock = scope.clock
         val computeScheduler = FilterScheduler(
-            filters = listOf(ComputeFilter(), ComputeCapabilitiesFilter()),
-            weighers = listOf(MemoryWeigher() to -1.0)
+            filters = listOf(ComputeFilter(), VCpuFilter(allocationRatio = 1.0), RamFilter(allocationRatio = 1.0)),
+            weighers = listOf(RamWeigher())
         )
-        val meter = MeterProvider.noop().get("opendc-compute")
-        service = ComputeService(scope.coroutineContext, clock, meter, computeScheduler)
+        service = ComputeService(scope.coroutineContext, clock, MeterProvider.noop(), computeScheduler)
     }
 
     @Test
@@ -167,9 +167,9 @@ internal class ComputeServiceTest {
         val server = client.newServer("test", image, flavor, start = false)
 
         server.start()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
         server.refresh()
-        assertEquals(ServerState.ERROR, server.state)
+        assertEquals(ServerState.TERMINATED, server.state)
     }
 
     @Test
@@ -180,9 +180,9 @@ internal class ComputeServiceTest {
         val server = client.newServer("test", image, flavor, start = false)
 
         server.start()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
         server.refresh()
-        assertEquals(ServerState.ERROR, server.state)
+        assertEquals(ServerState.TERMINATED, server.state)
     }
 
     @Test
@@ -193,9 +193,9 @@ internal class ComputeServiceTest {
         val server = client.newServer("test", image, flavor, start = false)
 
         server.start()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
         server.refresh()
-        assertEquals(ServerState.ERROR, server.state)
+        assertEquals(ServerState.TERMINATED, server.state)
     }
 
     @Test
@@ -207,7 +207,7 @@ internal class ComputeServiceTest {
 
         server.start()
         server.stop()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
         server.refresh()
         assertEquals(ServerState.TERMINATED, server.state)
     }
@@ -228,7 +228,7 @@ internal class ComputeServiceTest {
         val server = client.newServer("test", image, flavor, start = false)
 
         server.start()
-        delay(10 * 60 * 1000)
+        delay(10L * 60 * 1000)
         server.refresh()
         assertEquals(ServerState.PROVISIONING, server.state)
 
@@ -254,12 +254,12 @@ internal class ComputeServiceTest {
         val server = client.newServer("test", image, flavor, start = false)
 
         server.start()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
 
         every { host.state } returns HostState.UP
         listeners.forEach { it.onStateChanged(host, HostState.UP) }
 
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
         server.refresh()
         assertEquals(ServerState.PROVISIONING, server.state)
 
@@ -284,13 +284,13 @@ internal class ComputeServiceTest {
         val image = client.newImage("test")
         val server = client.newServer("test", image, flavor, start = false)
 
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
 
         every { host.state } returns HostState.DOWN
         listeners.forEach { it.onStateChanged(host, HostState.DOWN) }
 
         server.start()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
         server.refresh()
         assertEquals(ServerState.PROVISIONING, server.state)
 
@@ -344,7 +344,7 @@ internal class ComputeServiceTest {
 
         // Start server
         server.start()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
         coVerify { host.spawn(capture(slot), true) }
 
         listeners.forEach { it.onStateChanged(host, slot.captured, ServerState.RUNNING) }
@@ -383,7 +383,7 @@ internal class ComputeServiceTest {
         val server = client.newServer("test", image, flavor, start = false)
 
         server.start()
-        delay(5 * 60 * 1000)
+        delay(5L * 60 * 1000)
 
         server.refresh()
         assertEquals(ServerState.PROVISIONING, server.state)
diff --git a/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/InternalServerTest.kt b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/InternalServerTest.kt
index 20ea8d20..dfd3bc67 100644
--- a/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/InternalServerTest.kt
+++ b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/InternalServerTest.kt
@@ -47,8 +47,9 @@ class InternalServerTest {
     fun testEquality() {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
+
         val a = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
         val b = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
@@ -59,8 +60,8 @@ class InternalServerTest {
     fun testEqualityWithDifferentType() {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val a = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         val b = mockk<Server>(relaxUnitFun = true)
@@ -73,8 +74,8 @@ class InternalServerTest {
     fun testInequalityWithDifferentType() {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val a = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         val b = mockk<Server>(relaxUnitFun = true)
@@ -87,8 +88,8 @@ class InternalServerTest {
     fun testInequalityWithIncorrectType() {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val a = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         assertNotEquals(a, Unit)
@@ -98,11 +99,11 @@ class InternalServerTest {
     fun testStartTerminatedServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
-        every { service.schedule(any()) } answers { ComputeServiceImpl.SchedulingRequest(it.invocation.args[0] as InternalServer) }
+        every { service.schedule(any()) } answers { ComputeServiceImpl.SchedulingRequest(it.invocation.args[0] as InternalServer, 0) }
 
         server.start()
 
@@ -114,8 +115,8 @@ class InternalServerTest {
     fun testStartDeletedServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         server.state = ServerState.DELETED
@@ -127,8 +128,8 @@ class InternalServerTest {
     fun testStartProvisioningServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         server.state = ServerState.PROVISIONING
@@ -142,8 +143,8 @@ class InternalServerTest {
     fun testStartRunningServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         server.state = ServerState.RUNNING
@@ -157,10 +158,10 @@ class InternalServerTest {
     fun testStopProvisioningServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
-        val request = ComputeServiceImpl.SchedulingRequest(server)
+        val request = ComputeServiceImpl.SchedulingRequest(server, 0)
 
         every { service.schedule(any()) } returns request
 
@@ -175,8 +176,8 @@ class InternalServerTest {
     fun testStopTerminatedServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         server.state = ServerState.TERMINATED
@@ -189,8 +190,8 @@ class InternalServerTest {
     fun testStopDeletedServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         server.state = ServerState.DELETED
@@ -203,8 +204,8 @@ class InternalServerTest {
     fun testStopRunningServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>()
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
         val host = mockk<Host>(relaxUnitFun = true)
 
@@ -220,10 +221,10 @@ class InternalServerTest {
     fun testDeleteProvisioningServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>(relaxUnitFun = true)
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
-        val request = ComputeServiceImpl.SchedulingRequest(server)
+        val request = ComputeServiceImpl.SchedulingRequest(server, 0)
 
         every { service.schedule(any()) } returns request
 
@@ -239,8 +240,8 @@ class InternalServerTest {
     fun testDeleteTerminatedServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>(relaxUnitFun = true)
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         server.state = ServerState.TERMINATED
@@ -255,8 +256,8 @@ class InternalServerTest {
     fun testDeleteDeletedServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>(relaxUnitFun = true)
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
 
         server.state = ServerState.DELETED
@@ -269,8 +270,8 @@ class InternalServerTest {
     fun testDeleteRunningServer() = runBlockingSimulation {
         val service = mockk<ComputeServiceImpl>(relaxUnitFun = true)
         val uid = UUID.randomUUID()
-        val flavor = mockk<InternalFlavor>()
-        val image = mockk<InternalImage>()
+        val flavor = mockFlavor()
+        val image = mockImage()
         val server = InternalServer(service, uid, "test", flavor, image, mutableMapOf(), mutableMapOf())
         val host = mockk<Host>(relaxUnitFun = true)
 
@@ -282,4 +283,20 @@ class InternalServerTest {
         coVerify { host.delete(server) }
         verify { service.delete(server) }
     }
+
+    private fun mockFlavor(): InternalFlavor {
+        val flavor = mockk<InternalFlavor>()
+        every { flavor.name } returns "c5.large"
+        every { flavor.uid } returns UUID.randomUUID()
+        every { flavor.cpuCount } returns 2
+        every { flavor.memorySize } returns 4096
+        return flavor
+    }
+
+    private fun mockImage(): InternalImage {
+        val image = mockk<InternalImage>()
+        every { image.name } returns "ubuntu-20.04"
+        every { image.uid } returns UUID.randomUUID()
+        return image
+    }
 }
diff --git a/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/scheduler/FilterSchedulerTest.kt b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/scheduler/FilterSchedulerTest.kt
new file mode 100644
index 00000000..cafd4498
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/scheduler/FilterSchedulerTest.kt
@@ -0,0 +1,407 @@
+/*
+ * 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.compute.service.scheduler
+
+import io.mockk.every
+import io.mockk.mockk
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertNull
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertAll
+import org.junit.jupiter.api.assertThrows
+import org.opendc.compute.api.Server
+import org.opendc.compute.service.driver.HostModel
+import org.opendc.compute.service.driver.HostState
+import org.opendc.compute.service.internal.HostView
+import org.opendc.compute.service.scheduler.filters.ComputeFilter
+import org.opendc.compute.service.scheduler.filters.InstanceCountFilter
+import org.opendc.compute.service.scheduler.filters.RamFilter
+import org.opendc.compute.service.scheduler.filters.VCpuFilter
+import org.opendc.compute.service.scheduler.weights.CoreRamWeigher
+import org.opendc.compute.service.scheduler.weights.InstanceCountWeigher
+import org.opendc.compute.service.scheduler.weights.RamWeigher
+import org.opendc.compute.service.scheduler.weights.VCpuWeigher
+import java.util.*
+
+/**
+ * Test suite for the [FilterScheduler].
+ */
+internal class FilterSchedulerTest {
+    @Test
+    fun testInvalidSubsetSize() {
+        assertThrows<IllegalArgumentException> {
+            FilterScheduler(
+                filters = emptyList(),
+                weighers = emptyList(),
+                subsetSize = 0
+            )
+        }
+
+        assertThrows<IllegalArgumentException> {
+            FilterScheduler(
+                filters = emptyList(),
+                weighers = emptyList(),
+                subsetSize = -2
+            )
+        }
+    }
+
+    @Test
+    fun testNoHosts() {
+        val scheduler = FilterScheduler(
+            filters = emptyList(),
+            weighers = emptyList(),
+        )
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertNull(scheduler.select(server))
+    }
+
+    @Test
+    fun testNoFiltersAndSchedulers() {
+        val scheduler = FilterScheduler(
+            filters = emptyList(),
+            weighers = emptyList(),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.DOWN
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        // Make sure we get the first host both times
+        assertAll(
+            { assertEquals(hostA, scheduler.select(server)) },
+            { assertEquals(hostA, scheduler.select(server)) }
+        )
+    }
+
+    @Test
+    fun testNoFiltersAndSchedulersRandom() {
+        val scheduler = FilterScheduler(
+            filters = emptyList(),
+            weighers = emptyList(),
+            subsetSize = Int.MAX_VALUE,
+            random = Random(1)
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.DOWN
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        // Make sure we get the first host both times
+        assertAll(
+            { assertEquals(hostB, scheduler.select(server)) },
+            { assertEquals(hostA, scheduler.select(server)) }
+        )
+    }
+
+    @Test
+    fun testHostIsDown() {
+        val scheduler = FilterScheduler(
+            filters = listOf(ComputeFilter()),
+            weighers = emptyList(),
+        )
+
+        val host = mockk<HostView>()
+        every { host.host.state } returns HostState.DOWN
+
+        scheduler.addHost(host)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertNull(scheduler.select(server))
+    }
+
+    @Test
+    fun testHostIsUp() {
+        val scheduler = FilterScheduler(
+            filters = listOf(ComputeFilter()),
+            weighers = emptyList(),
+        )
+
+        val host = mockk<HostView>()
+        every { host.host.state } returns HostState.UP
+
+        scheduler.addHost(host)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(host, scheduler.select(server))
+    }
+
+    @Test
+    fun testRamFilter() {
+        val scheduler = FilterScheduler(
+            filters = listOf(RamFilter(1.0)),
+            weighers = emptyList(),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4, 2048)
+        every { hostA.availableMemory } returns 512
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4, 2048)
+        every { hostB.availableMemory } returns 2048
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(hostB, scheduler.select(server))
+    }
+
+    @Test
+    fun testRamFilterOvercommit() {
+        val scheduler = FilterScheduler(
+            filters = listOf(RamFilter(1.5)),
+            weighers = emptyList(),
+        )
+
+        val host = mockk<HostView>()
+        every { host.host.state } returns HostState.UP
+        every { host.host.model } returns HostModel(4, 2048)
+        every { host.availableMemory } returns 2048
+
+        scheduler.addHost(host)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 2300
+
+        assertNull(scheduler.select(server))
+    }
+
+    @Test
+    fun testVCpuFilter() {
+        val scheduler = FilterScheduler(
+            filters = listOf(VCpuFilter(1.0)),
+            weighers = emptyList(),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4, 2048)
+        every { hostA.provisionedCores } returns 3
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4, 2048)
+        every { hostB.provisionedCores } returns 0
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(hostB, scheduler.select(server))
+    }
+
+    @Test
+    fun testVCpuFilterOvercommit() {
+        val scheduler = FilterScheduler(
+            filters = listOf(VCpuFilter(16.0)),
+            weighers = emptyList(),
+        )
+
+        val host = mockk<HostView>()
+        every { host.host.state } returns HostState.UP
+        every { host.host.model } returns HostModel(4, 2048)
+        every { host.provisionedCores } returns 0
+
+        scheduler.addHost(host)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 8
+        every { server.flavor.memorySize } returns 1024
+
+        assertNull(scheduler.select(server))
+    }
+
+    @Test
+    fun testInstanceCountFilter() {
+        val scheduler = FilterScheduler(
+            filters = listOf(InstanceCountFilter(limit = 2)),
+            weighers = emptyList(),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4, 2048)
+        every { hostA.instanceCount } returns 2
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4, 2048)
+        every { hostB.instanceCount } returns 0
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(hostB, scheduler.select(server))
+    }
+
+    @Test
+    fun testRamWeigher() {
+        val scheduler = FilterScheduler(
+            filters = emptyList(),
+            weighers = listOf(RamWeigher(1.5)),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4, 2048)
+        every { hostA.availableMemory } returns 1024
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4, 2048)
+        every { hostB.availableMemory } returns 512
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(hostA, scheduler.select(server))
+    }
+
+    @Test
+    fun testCoreRamWeigher() {
+        val scheduler = FilterScheduler(
+            filters = emptyList(),
+            weighers = listOf(CoreRamWeigher(1.5)),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(12, 2048)
+        every { hostA.availableMemory } returns 1024
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4, 2048)
+        every { hostB.availableMemory } returns 512
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(hostB, scheduler.select(server))
+    }
+
+    @Test
+    fun testVCpuWeigher() {
+        val scheduler = FilterScheduler(
+            filters = emptyList(),
+            weighers = listOf(VCpuWeigher(16.0)),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4, 2048)
+        every { hostA.provisionedCores } returns 2
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4, 2048)
+        every { hostB.provisionedCores } returns 0
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(hostB, scheduler.select(server))
+    }
+
+    @Test
+    fun testInstanceCountWeigher() {
+        val scheduler = FilterScheduler(
+            filters = emptyList(),
+            weighers = listOf(InstanceCountWeigher(multiplier = -1.0)),
+        )
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4, 2048)
+        every { hostA.instanceCount } returns 2
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4, 2048)
+        every { hostB.instanceCount } returns 0
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val server = mockk<Server>()
+        every { server.flavor.cpuCount } returns 2
+        every { server.flavor.memorySize } returns 1024
+
+        assertEquals(hostB, scheduler.select(server))
+    }
+}