refactor(compute): Expose CPU and system stats via Host interface

This change updates the `Host` interface to directly expose CPU and
system stats to be used by components that interface with the `Host`
interface.

Previously, this would require the user to interact with the OpenTelemetry SDK.
Although that is still possible for more advanced usage cases, users can
use the following methods to easily access common host and guest
statistics.

8 files changed, 363 insertions, 110 deletions

diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/Host.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/Host.kt
index bed15dfd..67b144d9 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/Host.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/Host.kt
@@ -23,6 +23,10 @@
 package org.opendc.compute.service.driver
 
 import org.opendc.compute.api.Server
+import org.opendc.compute.service.driver.telemetry.GuestCpuStats
+import org.opendc.compute.service.driver.telemetry.GuestSystemStats
+import org.opendc.compute.service.driver.telemetry.HostCpuStats
+import org.opendc.compute.service.driver.telemetry.HostSystemStats
 import java.util.*
 
 /**
@@ -55,6 +59,11 @@ public interface Host {
     public val meta: Map<String, Any>
 
     /**
+     * The [Server] instances known to the host.
+     */
+    public val instances: Set<Server>
+
+    /**
      * Determine whether the specified [instance][server] can still fit on this host.
      */
     public fun canFit(server: Server): Boolean
@@ -100,4 +109,30 @@ public interface Host {
      * Remove a [HostListener] from this host.
      */
     public fun removeListener(listener: HostListener)
+
+    /**
+     * Query the system statistics of the host.
+     */
+    public fun getSystemStats(): HostSystemStats
+
+    /**
+     * Query the system statistics of a [Server] that is located on this host.
+     *
+     * @param server The [Server] to obtain the system statistics of.
+     * @throws IllegalArgumentException if the server is not present on the host.
+     */
+    public fun getSystemStats(server: Server): GuestSystemStats
+
+    /**
+     * Query the CPU statistics of the host.
+     */
+    public fun getCpuStats(): HostCpuStats
+
+    /**
+     * Query the CPU statistics of a [Server] that is located on this host.
+     *
+     * @param server The [Server] to obtain the CPU statistics of.
+     * @throws IllegalArgumentException if the server is not present on the host.
+     */
+    public fun getCpuStats(server: Server): GuestCpuStats
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/GuestCpuStats.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/GuestCpuStats.kt
new file mode 100644
index 00000000..b5d63471
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/GuestCpuStats.kt
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2022 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.driver.telemetry
+
+/**
+ * Statistics about the CPUs of a guest.
+ *
+ * @property activeTime The cumulative time (in seconds) that the CPUs of the guest were actively running.
+ * @property idleTime The cumulative time (in seconds) the CPUs of the guest were idle.
+ * @property stealTime The cumulative CPU time (in seconds) that the guest was ready to run, but not granted time by the host.
+ * @property lostTime The cumulative CPU time (in seconds) that was lost due to interference with other machines.
+ * @property capacity The available CPU capacity of the guest (in MHz).
+ * @property usage Amount of CPU resources (in MHz) actually used by the guest.
+ * @property utilization Utilization of the CPU resources (in %) relative to the total CPU capacity.
+ */
+public data class GuestCpuStats(
+    val activeTime: Long,
+    val idleTime: Long,
+    val stealTime: Long,
+    val lostTime: Long,
+    val capacity: Double,
+    val usage: Double,
+    val utilization: Double
+)
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/GuestSystemStats.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/GuestSystemStats.kt
new file mode 100644
index 00000000..b3958473
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/GuestSystemStats.kt
@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2022 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.driver.telemetry
+
+import java.time.Duration
+import java.time.Instant
+
+/**
+ * System-level statistics of a guest.
+ *
+ * @property uptime The cumulative uptime of the guest since last boot (in ms).
+ * @property downtime The cumulative downtime of the guest since last boot (in ms).
+ * @property bootTime The time at which the guest booted.
+ */
+public data class GuestSystemStats(
+    val uptime: Duration,
+    val downtime: Duration,
+    val bootTime: Instant
+)
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/HostCpuStats.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/HostCpuStats.kt
new file mode 100644
index 00000000..55e23c0e
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/HostCpuStats.kt
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2022 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.driver.telemetry
+
+/**
+ * Statistics about the CPUs of a host.
+ *
+ * @property activeTime The cumulative time (in seconds) that the CPUs of the host were actively running.
+ * @property idleTime The cumulative time (in seconds) the CPUs of the host were idle.
+ * @property stealTime The cumulative CPU time (in seconds) that virtual machines were ready to run, but were not able to.
+ * @property lostTime The cumulative CPU time (in seconds) that was lost due to interference between virtual machines.
+ * @property capacity The available CPU capacity of the host (in MHz).
+ * @property demand Amount of CPU resources (in MHz) the guests would use if there were no CPU contention or CPU
+ *                  limits.
+ * @property usage Amount of CPU resources (in MHz) actually used by the host.
+ * @property utilization Utilization of the CPU resources (in %) relative to the total CPU capacity.
+ */
+public data class HostCpuStats(
+    val activeTime: Long,
+    val idleTime: Long,
+    val stealTime: Long,
+    val lostTime: Long,
+    val capacity: Double,
+    val demand: Double,
+    val usage: Double,
+    val utilization: Double
+)
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/HostSystemStats.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/HostSystemStats.kt
new file mode 100644
index 00000000..1c07023f
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/driver/telemetry/HostSystemStats.kt
@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2022 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.driver.telemetry
+
+import java.time.Duration
+import java.time.Instant
+
+/**
+ * System-level statistics of a host.
+
+ * @property uptime The cumulative uptime of the host since last boot (in ms).
+ * @property downtime The cumulative downtime of the host since last boot (in ms).
+ * @property bootTime The time at which the server started.
+ * @property powerUsage Instantaneous power usage of the system (in W).
+ * @property energyUsage The cumulative energy usage of the system (in J).
+ * @property guestsTerminated The number of guests that are in a terminated state.
+ * @property guestsRunning The number of guests that are in a running state.
+ * @property guestsError The number of guests that are in an error state.
+ * @property guestsInvalid The number of guests that are in an unknown state.
+ */
+public data class HostSystemStats(
+    val uptime: Duration,
+    val downtime: Duration,
+    val bootTime: Instant,
+    val powerUsage: Double,
+    val energyUsage: Double,
+    val guestsTerminated: Int,
+    val guestsRunning: Int,
+    val guestsError: Int,
+    val guestsInvalid: Int,
+)
diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
index 4eb6392e..323ae4fe 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
@@ -29,11 +29,14 @@ import io.opentelemetry.api.metrics.MeterProvider
 import io.opentelemetry.api.metrics.ObservableDoubleMeasurement
 import io.opentelemetry.api.metrics.ObservableLongMeasurement
 import kotlinx.coroutines.*
-import mu.KotlinLogging
 import org.opendc.compute.api.Flavor
 import org.opendc.compute.api.Server
 import org.opendc.compute.api.ServerState
 import org.opendc.compute.service.driver.*
+import org.opendc.compute.service.driver.telemetry.GuestCpuStats
+import org.opendc.compute.service.driver.telemetry.GuestSystemStats
+import org.opendc.compute.service.driver.telemetry.HostCpuStats
+import org.opendc.compute.service.driver.telemetry.HostSystemStats
 import org.opendc.compute.simulator.internal.Guest
 import org.opendc.compute.simulator.internal.GuestListener
 import org.opendc.simulator.compute.*
@@ -49,6 +52,8 @@ import org.opendc.simulator.compute.power.PowerDriver
 import org.opendc.simulator.compute.power.SimplePowerDriver
 import org.opendc.simulator.compute.workload.SimWorkload
 import org.opendc.simulator.flow.FlowEngine
+import java.time.Duration
+import java.time.Instant
 import java.util.*
 import kotlin.coroutines.CoroutineContext
 
@@ -81,11 +86,6 @@ public class SimHost(
     private val clock = engine.clock
 
     /**
-     * The logger instance of this server.
-     */
-    private val logger = KotlinLogging.logger {}
-
-    /**
      * The [Meter] to track metrics of the simulated host.
      */
     private val meter = meterProvider.get("org.opendc.compute.simulator")
@@ -112,6 +112,9 @@ public class SimHost(
     private val guests = HashMap<Server, Guest>()
     private val _guests = mutableListOf<Guest>()
 
+    override val instances: Set<Server>
+        get() = guests.keys
+
     override val state: HostState
         get() = _state
     private var _state: HostState = HostState.DOWN
@@ -249,6 +252,68 @@ public class SimHost(
         machine.cancel()
     }
 
+    override fun getSystemStats(): HostSystemStats {
+        updateUptime()
+
+        var terminated = 0
+        var running = 0
+        var error = 0
+        var invalid = 0
+
+        val guests = _guests.listIterator()
+        for (guest in guests) {
+            when (guest.state) {
+                ServerState.TERMINATED -> terminated++
+                ServerState.RUNNING -> running++
+                ServerState.ERROR -> error++
+                ServerState.DELETED -> {
+                    // Remove guests that have been deleted
+                    this.guests.remove(guest.server)
+                    guests.remove()
+                }
+                else -> invalid++
+            }
+        }
+
+        return HostSystemStats(
+            Duration.ofMillis(_uptime),
+            Duration.ofMillis(_downtime),
+            Instant.ofEpochMilli(_bootTime),
+            machine.powerUsage,
+            machine.energyUsage,
+            terminated,
+            running,
+            error,
+            invalid
+        )
+    }
+
+    override fun getSystemStats(server: Server): GuestSystemStats {
+        val guest = requireNotNull(guests[server]) { "Unknown server ${server.uid} at host $uid" }
+        return guest.getSystemStats()
+    }
+
+    override fun getCpuStats(): HostCpuStats {
+        val counters = hypervisor.counters
+        counters.flush()
+
+        return HostCpuStats(
+            counters.cpuActiveTime / 1000L,
+            counters.cpuIdleTime / 1000L,
+            counters.cpuStealTime / 1000L,
+            counters.cpuLostTime / 1000L,
+            hypervisor.cpuCapacity,
+            hypervisor.cpuDemand,
+            hypervisor.cpuUsage,
+            hypervisor.cpuUsage / _cpuLimit
+        )
+    }
+
+    override fun getCpuStats(server: Server): GuestCpuStats {
+        val guest = requireNotNull(guests[server]) { "Unknown server ${server.uid} at host $uid" }
+        return guest.getCpuStats()
+    }
+
     override fun hashCode(): Int = uid.hashCode()
 
     override fun equals(other: Any?): Boolean {
@@ -417,13 +482,12 @@ public class SimHost(
      * Helper function to track the CPU time of a machine.
      */
     private fun collectCpuTime(result: ObservableLongMeasurement) {
-        val counters = hypervisor.counters
-        counters.flush()
+        val stats = getCpuStats()
 
-        result.record(counters.cpuActiveTime / 1000L, _activeState)
-        result.record(counters.cpuIdleTime / 1000L, _idleState)
-        result.record(counters.cpuStealTime / 1000L, _stealState)
-        result.record(counters.cpuLostTime / 1000L, _lostState)
+        result.record(stats.activeTime, _activeState)
+        result.record(stats.idleTime, _idleState)
+        result.record(stats.stealTime, _stealState)
+        result.record(stats.lostTime, _lostState)
 
         val guests = _guests
         for (i in guests.indices) {
@@ -450,7 +514,7 @@ public class SimHost(
 
         val guests = _guests
         for (i in guests.indices) {
-            guests[i].updateUptime(duration)
+            guests[i].updateUptime()
         }
     }
 
diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt
index bb378ee3..0d4c550d 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt
@@ -32,6 +32,8 @@ import kotlinx.coroutines.*
 import mu.KotlinLogging
 import org.opendc.compute.api.Server
 import org.opendc.compute.api.ServerState
+import org.opendc.compute.service.driver.telemetry.GuestCpuStats
+import org.opendc.compute.service.driver.telemetry.GuestSystemStats
 import org.opendc.compute.simulator.SimHost
 import org.opendc.compute.simulator.SimWorkloadMapper
 import org.opendc.simulator.compute.kernel.SimHypervisor
@@ -39,6 +41,8 @@ import org.opendc.simulator.compute.kernel.SimVirtualMachine
 import org.opendc.simulator.compute.runWorkload
 import org.opendc.simulator.compute.workload.SimWorkload
 import java.time.Clock
+import java.time.Duration
+import java.time.Instant
 import kotlin.coroutines.CoroutineContext
 
 /**
@@ -146,6 +150,37 @@ internal class Guest(
     }
 
     /**
+     * Obtain the system statistics of this guest.
+     */
+    fun getSystemStats(): GuestSystemStats {
+        updateUptime()
+
+        return GuestSystemStats(
+            Duration.ofMillis(_uptime),
+            Duration.ofMillis(_downtime),
+            Instant.ofEpochMilli(_bootTime)
+        )
+    }
+
+    /**
+     * Obtain the CPU statistics of this guest.
+     */
+    fun getCpuStats(): GuestCpuStats {
+        val counters = machine.counters
+        counters.flush()
+
+        return GuestCpuStats(
+            counters.cpuActiveTime / 1000L,
+            counters.cpuIdleTime / 1000L,
+            counters.cpuStealTime / 1000L,
+            counters.cpuLostTime / 1000L,
+            machine.cpuCapacity,
+            machine.cpuUsage,
+            machine.cpuUsage / _cpuLimit
+        )
+    }
+
+    /**
      * The [Job] representing the current active virtual machine instance or `null` if no virtual machine is active.
      */
     private var job: Job? = null
@@ -209,6 +244,8 @@ internal class Guest(
      * This method is invoked when the guest stopped.
      */
     private fun onStop(target: ServerState) {
+        updateUptime()
+
         state = target
         listener.onStop(this)
     }
@@ -224,10 +261,16 @@ internal class Guest(
         .put(STATE_KEY, "down")
         .build()
 
+    private var _lastReport = clock.millis()
+
     /**
      * Helper function to track the uptime and downtime of the guest.
      */
-    fun updateUptime(duration: Long) {
+    fun updateUptime() {
+        val now = clock.millis()
+        val duration = now - _lastReport
+        _lastReport = now
+
         if (state == ServerState.RUNNING) {
             _uptime += duration
         } else if (state == ServerState.ERROR) {
@@ -239,6 +282,8 @@ internal class Guest(
      * Helper function to track the uptime of the guest.
      */
     fun collectUptime(result: ObservableLongMeasurement) {
+        updateUptime()
+
         result.record(_uptime, _upState)
         result.record(_downtime, _downState)
     }
diff --git a/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/SimHostTest.kt b/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/SimHostTest.kt
index f0325023..67689dc8 100644
--- a/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/SimHostTest.kt
+++ b/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/SimHostTest.kt
@@ -22,8 +22,7 @@
 
 package org.opendc.compute.simulator
 
-import io.opentelemetry.sdk.metrics.SdkMeterProvider
-import io.opentelemetry.sdk.resources.Resource
+import io.opentelemetry.api.metrics.MeterProvider
 import kotlinx.coroutines.*
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.BeforeEach
@@ -42,13 +41,6 @@ import org.opendc.simulator.compute.workload.SimTraceFragment
 import org.opendc.simulator.compute.workload.SimTraceWorkload
 import org.opendc.simulator.core.runBlockingSimulation
 import org.opendc.simulator.flow.FlowEngine
-import org.opendc.telemetry.compute.ComputeMetricExporter
-import org.opendc.telemetry.compute.HOST_ID
-import org.opendc.telemetry.compute.table.HostTableReader
-import org.opendc.telemetry.compute.table.ServerTableReader
-import org.opendc.telemetry.sdk.metrics.export.CoroutineMetricReader
-import org.opendc.telemetry.sdk.toOtelClock
-import java.time.Duration
 import java.util.*
 import kotlin.coroutines.resume
 
@@ -73,45 +65,16 @@ internal class SimHostTest {
      */
     @Test
     fun testOvercommitted() = runBlockingSimulation {
-        var idleTime = 0L
-        var activeTime = 0L
-        var stealTime = 0L
-
-        val hostId = UUID.randomUUID()
-        val hostResource = Resource.builder()
-            .put(HOST_ID, hostId.toString())
-            .build()
-
-        // Setup metric reader
         val duration = 5 * 60L
-        val reader = CoroutineMetricReader(
-            this,
-            object : ComputeMetricExporter() {
-                override fun record(reader: HostTableReader) {
-                    activeTime += reader.cpuActiveTime
-                    idleTime += reader.cpuIdleTime
-                    stealTime += reader.cpuStealTime
-                }
-            },
-            exportInterval = Duration.ofSeconds(duration)
-        )
-
-        val meterProvider = SdkMeterProvider
-            .builder()
-            .setResource(hostResource)
-            .setClock(clock.toOtelClock())
-            .registerMetricReader(reader)
-            .build()
-
         val engine = FlowEngine(coroutineContext, clock)
-        val virtDriver = SimHost(
-            uid = hostId,
+        val host = SimHost(
+            uid = UUID.randomUUID(),
             name = "test",
             model = machineModel,
             meta = emptyMap(),
             coroutineContext,
             engine,
-            meterProvider,
+            MeterProvider.noop(),
             SimFairShareHypervisorProvider()
         )
         val vmImageA = MockImage(
@@ -150,11 +113,11 @@ internal class SimHostTest {
         val flavor = MockFlavor(2, 0)
 
         coroutineScope {
-            launch { virtDriver.spawn(MockServer(UUID.randomUUID(), "a", flavor, vmImageA)) }
-            launch { virtDriver.spawn(MockServer(UUID.randomUUID(), "b", flavor, vmImageB)) }
+            launch { host.spawn(MockServer(UUID.randomUUID(), "a", flavor, vmImageA)) }
+            launch { host.spawn(MockServer(UUID.randomUUID(), "b", flavor, vmImageB)) }
 
             suspendCancellableCoroutine<Unit> { cont ->
-                virtDriver.addListener(object : HostListener {
+                host.addListener(object : HostListener {
                     private var finished = 0
 
                     override fun onStateChanged(host: Host, server: Server, newState: ServerState) {
@@ -168,13 +131,14 @@ internal class SimHostTest {
 
         // Ensure last cycle is collected
         delay(1000L * duration)
-        virtDriver.close()
-        meterProvider.close()
+        host.close()
+
+        val cpuStats = host.getCpuStats()
 
         assertAll(
-            { assertEquals(658, activeTime, "Active time does not match") },
-            { assertEquals(2341, idleTime, "Idle time does not match") },
-            { assertEquals(637, stealTime, "Steal time does not match") },
+            { assertEquals(658, cpuStats.activeTime, "Active time does not match") },
+            { assertEquals(2341, cpuStats.idleTime, "Idle time does not match") },
+            { assertEquals(637, cpuStats.stealTime, "Steal time does not match") },
             { assertEquals(1500001, clock.millis()) }
         )
     }
@@ -184,54 +148,16 @@ internal class SimHostTest {
      */
     @Test
     fun testFailure() = runBlockingSimulation {
-        var activeTime = 0L
-        var idleTime = 0L
-        var uptime = 0L
-        var downtime = 0L
-        var guestUptime = 0L
-        var guestDowntime = 0L
-
-        val hostId = UUID.randomUUID()
-        val hostResource = Resource.builder()
-            .put(HOST_ID, hostId.toString())
-            .build()
-
-        // Setup metric reader
         val duration = 5 * 60L
-        val reader = CoroutineMetricReader(
-            this,
-            object : ComputeMetricExporter() {
-                override fun record(reader: HostTableReader) {
-                    activeTime += reader.cpuActiveTime
-                    idleTime += reader.cpuIdleTime
-                    uptime += reader.uptime
-                    downtime += reader.downtime
-                }
-
-                override fun record(reader: ServerTableReader) {
-                    guestUptime += reader.uptime
-                    guestDowntime += reader.downtime
-                }
-            },
-            exportInterval = Duration.ofSeconds(duration)
-        )
-
-        val meterProvider = SdkMeterProvider
-            .builder()
-            .setResource(hostResource)
-            .setClock(clock.toOtelClock())
-            .registerMetricReader(reader)
-            .build()
-
         val engine = FlowEngine(coroutineContext, clock)
         val host = SimHost(
-            uid = hostId,
+            uid = UUID.randomUUID(),
             name = "test",
             model = machineModel,
             meta = emptyMap(),
             coroutineContext,
             engine,
-            meterProvider,
+            MeterProvider.noop(),
             SimFairShareHypervisorProvider()
         )
         val image = MockImage(
@@ -275,15 +201,17 @@ internal class SimHostTest {
         // Ensure last cycle is collected
         delay(1000L * duration)
 
-        meterProvider.close()
+        val cpuStats = host.getCpuStats()
+        val sysStats = host.getSystemStats()
+        val guestSysStats = host.getSystemStats(server)
 
         assertAll(
-            { assertEquals(1775, idleTime, "Idle time does not match") },
-            { assertEquals(624, activeTime, "Active time does not match") },
-            { assertEquals(900001, uptime, "Uptime does not match") },
-            { assertEquals(300000, downtime, "Downtime does not match") },
-            { assertEquals(900000, guestUptime, "Guest uptime does not match") },
-            { assertEquals(300000, guestDowntime, "Guest downtime does not match") },
+            { assertEquals(1775, cpuStats.idleTime, "Idle time does not match") },
+            { assertEquals(624, cpuStats.activeTime, "Active time does not match") },
+            { assertEquals(900001, sysStats.uptime.toMillis(), "Uptime does not match") },
+            { assertEquals(300000, sysStats.downtime.toMillis(), "Downtime does not match") },
+            { assertEquals(900001, guestSysStats.uptime.toMillis(), "Guest uptime does not match") },
+            { assertEquals(300000, guestSysStats.downtime.toMillis(), "Guest downtime does not match") },
         )
     }