feat(compute): Add support for affinity scheduling (#101)

This change adds support for (anti-)affinity scheduling of servers onto hosts, 
which happens at the compute service level. 
In the future, we might add support for server groups, which also enables 
soft (anti-)affinity scheduling.

Implements #26

## Implementation Notes :hammer_and_pick:

* Add `DifferentHostFilter` to schedule instances on different hosts from a set of instances.
* Add `SameHostFilter` to schedule instances on the same hosts as a set of instances.

3 files changed, 154 insertions, 0 deletions

diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/DifferentHostFilter.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/DifferentHostFilter.kt
new file mode 100644
index 00000000..54f2f303
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/DifferentHostFilter.kt
@@ -0,0 +1,38 @@
+/*
+ * 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.scheduler.filters
+
+import org.opendc.compute.api.Server
+import org.opendc.compute.service.internal.HostView
+import java.util.*
+
+/**
+ * A [HostFilter] that ensures an instance is scheduled on a different host from a set of instances.
+ */
+public class DifferentHostFilter : HostFilter {
+    override fun test(host: HostView, server: Server): Boolean {
+        @Suppress("UNCHECKED_CAST")
+        val affinityUUIDs = server.meta["scheduler_hint:different_host"] as? Set<UUID> ?: return true
+        return host.host.instances.none { it.uid in affinityUUIDs }
+    }
+}
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/SameHostFilter.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/SameHostFilter.kt
new file mode 100644
index 00000000..febb085d
--- /dev/null
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/filters/SameHostFilter.kt
@@ -0,0 +1,38 @@
+/*
+ * 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.scheduler.filters
+
+import org.opendc.compute.api.Server
+import org.opendc.compute.service.internal.HostView
+import java.util.*
+
+/**
+ * A [HostFilter] that ensures an instance is scheduled on the same host as all other instances in a set of instances.
+ */
+public class SameHostFilter : HostFilter {
+    override fun test(host: HostView, server: Server): Boolean {
+        @Suppress("UNCHECKED_CAST")
+        val affinityUUIDs = server.meta["scheduler_hint:same_host"] as? Set<UUID> ?: return true
+        return host.host.instances.any { it.uid in affinityUUIDs }
+    }
+}
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
index 3f2ce43b..350ac944 100644
--- 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
@@ -323,6 +323,84 @@ internal class FilterSchedulerTest {
     }
 
     @Test
+    fun testAffinityFilter() {
+        val scheduler = FilterScheduler(
+            filters = listOf(SameHostFilter()),
+            weighers = emptyList(),
+        )
+
+        val serverA = mockk<Server>()
+        every { serverA.uid } returns UUID.randomUUID()
+        every { serverA.flavor.cpuCount } returns 2
+        every { serverA.flavor.memorySize } returns 1024
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4 * 2600.0, 4, 2048)
+        every { hostA.host.instances } returns emptySet()
+        every { hostA.provisionedCores } returns 3
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4 * 2600.0, 4, 2048)
+        every { hostB.host.instances } returns setOf(serverA)
+        every { hostB.provisionedCores } returns 0
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val serverB = mockk<Server>()
+        every { serverB.flavor.cpuCount } returns 2
+        every { serverB.flavor.memorySize } returns 1024
+        every { serverB.meta } returns emptyMap()
+
+        assertEquals(hostA, scheduler.select(serverB))
+
+        every { serverB.meta } returns mapOf("scheduler_hint:same_host" to setOf(serverA.uid))
+
+        assertEquals(hostB, scheduler.select(serverB))
+    }
+
+    @Test
+    fun testAntiAffinityFilter() {
+        val scheduler = FilterScheduler(
+            filters = listOf(DifferentHostFilter()),
+            weighers = emptyList(),
+        )
+
+        val serverA = mockk<Server>()
+        every { serverA.uid } returns UUID.randomUUID()
+        every { serverA.flavor.cpuCount } returns 2
+        every { serverA.flavor.memorySize } returns 1024
+
+        val hostA = mockk<HostView>()
+        every { hostA.host.state } returns HostState.UP
+        every { hostA.host.model } returns HostModel(4 * 2600.0, 4, 2048)
+        every { hostA.host.instances } returns setOf(serverA)
+        every { hostA.provisionedCores } returns 3
+
+        val hostB = mockk<HostView>()
+        every { hostB.host.state } returns HostState.UP
+        every { hostB.host.model } returns HostModel(4 * 2600.0, 4, 2048)
+        every { hostB.host.instances } returns emptySet()
+        every { hostB.provisionedCores } returns 0
+
+        scheduler.addHost(hostA)
+        scheduler.addHost(hostB)
+
+        val serverB = mockk<Server>()
+        every { serverB.flavor.cpuCount } returns 2
+        every { serverB.flavor.memorySize } returns 1024
+        every { serverB.meta } returns emptyMap()
+
+        assertEquals(hostA, scheduler.select(serverB))
+
+        every { serverB.meta } returns mapOf("scheduler_hint:different_host" to setOf(serverA.uid))
+
+        assertEquals(hostB, scheduler.select(serverB))
+    }
+
+    @Test
     fun testRamWeigher() {
         val scheduler = FilterScheduler(
             filters = emptyList(),