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.

2 files changed, 76 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 }
+    }
+}