Add allocation_fallback_strategy option as fallback strategy for per-node strategy

cmd/otel-allocator/allocation/per_node.go

@@ -25,12 +25,14 @@ const perNodeStrategyName = "per-node"
 var _ Strategy = &perNodeStrategy{}
 
 type perNodeStrategy struct {
-	collectorByNode map[string]*Collector
+	collectorByNode  map[string]*Collector
+	fallbackStrategy Strategy
 }
 
-func newPerNodeStrategy() Strategy {
+func newPerNodeStrategy(fallbackStrategy Strategy) Strategy {
 	return &perNodeStrategy{
-		collectorByNode: make(map[string]*Collector),
+		collectorByNode:  make(map[string]*Collector),
+		fallbackStrategy: fallbackStrategy,
 	}
 }
 
@@ -40,6 +42,10 @@ func (s *perNodeStrategy) GetName() string {
 
 func (s *perNodeStrategy) GetCollectorForTarget(collectors map[string]*Collector, item *target.Item) (*Collector, error) {
 	targetNodeName := item.GetNodeName()
+	if targetNodeName == "" {
+		return s.fallbackStrategy.GetCollectorForTarget(collectors, item)
+	}
+
 	collector, ok := s.collectorByNode[targetNodeName]
 	if !ok {
 		return nil, fmt.Errorf("could not find collector for node %s", targetNodeName)
@@ -54,4 +60,5 @@ func (s *perNodeStrategy) SetCollectors(collectors map[string]*Collector) {
 			s.collectorByNode[collector.NodeName] = collector
 		}
 	}
+	s.fallbackStrategy.SetCollectors(collectors)
 }

cmd/otel-allocator/allocation/per_node_test.go

@@ -26,6 +26,15 @@ import (
 
 var loggerPerNode = logf.Log.WithName("unit-tests")
 
+func GetTargetsWithNodeName(targets []*target.Item) (targetsWithNodeName []*target.Item) {
+	for _, item := range targets {
+		if item.GetNodeName() != "" {
+			targetsWithNodeName = append(targetsWithNodeName, item)
+		}
+	}
+	return targetsWithNodeName
+}
+
 // Tests that two targets with the same target url and job name but different label set are both added.
 func TestAllocationPerNode(t *testing.T) {
 	// prepare allocator with initial targets and collectors
@@ -83,13 +92,18 @@ func TestAllocationPerNode(t *testing.T) {
 		// only the first two targets should be allocated
 		itemsForCollector := s.GetTargetsForCollectorAndJob(actualItem.CollectorName, actualItem.JobName)
 
-		// first two should be assigned one to each collector; if third target, should not be assigned
+		// first two should be assigned one to each collector; if third target, it should be assigned
+		// according to the fallback strategy which may assign it to the otherwise empty collector or
+		// one of the others, depending on the strategy and collector loop order
 		if targetHash == thirdTarget.Hash() {
-			assert.Len(t, itemsForCollector, 0)
+			assert.Empty(t, item.GetNodeName())
+			assert.LessOrEqual(t, len(itemsForCollector), 2)
 			continue
 		}
-		assert.Len(t, itemsForCollector, 1)
-		assert.Equal(t, actualItem, itemsForCollector[0])
+
+		// Only check targets that have been assigned using the per-node (not fallback) strategy here
+		assert.Len(t, GetTargetsWithNodeName(itemsForCollector), 1)
+		assert.Equal(t, actualItem, GetTargetsWithNodeName(itemsForCollector)[0])
 	}
 }
 

cmd/otel-allocator/allocation/strategy.go

@@ -149,7 +149,7 @@ func init() {
 		panic(err)
 	}
 	err = Register(perNodeStrategyName, func(log logr.Logger, opts ...AllocationOption) Allocator {
-		return newAllocator(log, newPerNodeStrategy(), opts...)
+		return newAllocator(log, newPerNodeStrategy(newleastWeightedStrategy()), opts...)
 	})
 	if err != nil {
 		panic(err)