Added scheduler plugin functionality

docs/docs/plugin.md

@@ -190,6 +190,16 @@ Please see the [RunSpecValidator](https://github.com/mesosphere/marathon/blob/ma
 
 Marathon and the `RunSpecValidator` use the [Accord](https://github.com/wix/accord) validation library which is useful to understand when creating validator rules.
 
+## Scheduler
+
+#### mesosphere.marathon.plugin.scheduler.SchedulerPlugin
+
+This plugin allows to reject offers. Possible use-cases are:
+* Maintenance. Mark agent as going to maintenance and reject new offers from it.
+* Analytics. If task fails, for example, 5 times for 5 minutes, we can assume that it will fail again and reject new offers for it.
+* Binding to agents. For example, agents can be marked as included into primary or secondary group. Task can be marked with group name.
+ Plugin can schedule task deployment to primary agents. If all primary agents are busy, task can be scheduled to secondary agents
+
 ## Notes on Plugins
 
 * The plugins allow for the extension of behavior in Marathon.  They do NOT allow for replacement or removal of existing functionality.

plugin-interface/src/main/scala/mesosphere/marathon/plugin/scheduler/SchedulerPlugin.scala

@@ -0,0 +1,17 @@
+package mesosphere.marathon
+package plugin.scheduler
+
+import mesosphere.marathon.plugin.RunSpec
+import mesosphere.marathon.plugin.plugin.Plugin
+import org.apache.mesos.Protos.Offer
+
+/**
+  * Allows to use external logic to decline offers.
+  */
+trait SchedulerPlugin extends Plugin {
+
+  /**
+    * @return true if offer matches
+    */
+  def isMatch(offer: Offer, runSpec: RunSpec): Boolean
+}

src/main/scala/mesosphere/marathon/core/launcher/impl/InstanceOpFactoryImpl.scala

@@ -13,6 +13,7 @@ import mesosphere.marathon.core.plugin.PluginManager
 import mesosphere.marathon.core.pod.PodDefinition
 import mesosphere.marathon.core.task.Task
 import mesosphere.marathon.core.task.state.NetworkInfo
+import mesosphere.marathon.plugin.scheduler.SchedulerPlugin
 import mesosphere.marathon.plugin.task.RunSpecTaskProcessor
 import mesosphere.marathon.plugin.{ ApplicationSpec, PodSpec }
 import mesosphere.marathon.state._
@@ -39,6 +40,8 @@ class InstanceOpFactoryImpl(
     new InstanceOpFactoryHelper(principalOpt, roleOpt)
   }
 
+  private[this] val schedulerPlugins: Seq[SchedulerPlugin] = pluginManager.plugins[SchedulerPlugin]
+
   private[this] lazy val runSpecTaskProc: RunSpecTaskProcessor = combine(
     pluginManager.plugins[RunSpecTaskProcessor].toIndexedSeq)
 
@@ -153,7 +156,8 @@ class InstanceOpFactoryImpl(
         val resourceMatchResponse =
           ResourceMatcher.matchResources(
             offer, runSpec, instancesToConsiderForConstraints,
-            ResourceSelector.reservedWithLabels(rolesToConsider, reservationLabels)
+            ResourceSelector.reservedWithLabels(rolesToConsider, reservationLabels),
+            schedulerPlugins
           )
 
         resourceMatchResponse match {
@@ -179,7 +183,8 @@ class InstanceOpFactoryImpl(
       }
 
       val resourceMatchResponse =
-        ResourceMatcher.matchResources(offer, runSpec, instances.valuesIterator.toStream, ResourceSelector.reservable)
+        ResourceMatcher.matchResources(offer, runSpec, instances.valuesIterator.toStream, ResourceSelector.reservable,
+          schedulerPlugins)
       resourceMatchResponse match {
         case matches: ResourceMatchResponse.Match =>
           val instanceOp = reserveAndCreateVolumes(request.frameworkId, runSpec, offer, matches.resourceMatch)

src/main/scala/mesosphere/mesos/ResourceMatcher.scala

@@ -3,6 +3,7 @@ package mesosphere.mesos
 import com.typesafe.scalalogging.StrictLogging
 import mesosphere.marathon.core.instance.Instance
 import mesosphere.marathon.core.launcher.impl.TaskLabels
+import mesosphere.marathon.plugin.scheduler.SchedulerPlugin
 import mesosphere.marathon.state.{ DiskSource, DiskType, PersistentVolume, ResourceRole, RunSpec }
 import mesosphere.marathon.stream.Implicits._
 import mesosphere.marathon.tasks.{ PortsMatch, PortsMatcher, ResourceUtil }
@@ -129,7 +130,7 @@ object ResourceMatcher extends StrictLogging {
     * the reservation.
     */
   def matchResources(offer: Offer, runSpec: RunSpec, knownInstances: => Seq[Instance],
-    selector: ResourceSelector): ResourceMatchResponse = {
+    selector: ResourceSelector, schedulerPlugins: Seq[SchedulerPlugin] = Seq.empty): ResourceMatchResponse = {
 
     val groupedResources: Map[Role, Seq[Protos.Resource]] = offer.getResourcesList.groupBy(_.getName).map { case (k, v) => k -> v.to[Seq] }
 
@@ -194,7 +195,9 @@ object ResourceMatcher extends StrictLogging {
       badConstraints.isEmpty
     }
 
-    val resourceMatchOpt = if (scalarMatchResults.forall(_.matches) && meetsAllConstraints) {
+    val resourceMatchOpt = if (scalarMatchResults.forall(_.matches)
+      && meetsAllConstraints
+      && schedulerPlugins.forall(_.isMatch(offer, runSpec))) {
       portsMatchOpt match {
         case Some(portsMatch) =>
           Some(ResourceMatch(scalarMatchResults.collect { case m: ScalarMatch => m }, portsMatch))