adding oldest_create_index (#961)

CHANGELOG.md

@@ -3,20 +3,23 @@
 BUG FIXES:
 * config: Fixed a bug where the Nomad strategy and target plugins would fail to connect to Nomad's Task API socket [[GH-966](https://github.com/hashicorp/nomad-autoscaler/pull/966)]
 
+IMPROVEMENTS:
+* scaleutils: Add new node selector option `oldest_create_index` to select nodes with the oldest creation date  [[GH-961](https://github.com/hashicorp/nomad-autoscaler/pull/961)] 
+
 ## 0.4.5 (August 13, 2024)
 
 IMPROVEMENTS:
- * build: Updated to Go 1.22.6 and alpine to 3.20 [[GH-943](https://github.com/hashicorp/nomad-autoscaler/pull/943)]
- * build: Updated Nomad API dependency to 1.8.3 [[GH-950](https://github.com/hashicorp/nomad-autoscaler/pull/950)]
+* build: Updated to Go 1.22.6 and alpine to 3.20 [[GH-943](https://github.com/hashicorp/nomad-autoscaler/pull/943)]
+* build: Updated Nomad API dependency to 1.8.3 [[GH-950](https://github.com/hashicorp/nomad-autoscaler/pull/950)]
 
 BUG FIXES:
- * security: Fix incorrect conversion between integer types [[GH-946](https://github.com/hashicorp/nomad-autoscaler/pull/946)]
+* security: Fix incorrect conversion between integer types [[GH-946](https://github.com/hashicorp/nomad-autoscaler/pull/946)]
 
 ## 0.4.4 (June 4, 2024)
 
 IMPROVEMENTS:
- * agent: Update Nomad API dependency to v1.8.0 [[GH-909](https://github.com/hashicorp/nomad-autoscaler/pull/909)]
- * plugin/strategy/pass-through: Add new configuration `max_scale_up` and `max_scale_down` to allow restricting how much change is applied on each scaling event [[GH-881](https://github.com/hashicorp/nomad-autoscaler/pull/881)]
+* agent: Update Nomad API dependency to v1.8.0 [[GH-909](https://github.com/hashicorp/nomad-autoscaler/pull/909)]
+* plugin/strategy/pass-through: Add new configuration `max_scale_up` and `max_scale_down` to allow restricting how much change is applied on each scaling event [[GH-881](https://github.com/hashicorp/nomad-autoscaler/pull/881)]
 
 ## 0.4.3 (March 12, 2024)
 

sdk/helper/scaleutils/nodeselector/oldest_create_index.go

@@ -0,0 +1,43 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package nodeselector
+
+import (
+	"github.com/hashicorp/nomad-autoscaler/sdk"
+	"github.com/hashicorp/nomad/api"
+)
+
+// oldestCreateIndexClusterScaleInNodeSelector is the NodeSelector
+// implementation of the ClusterScaleInNodeSelector interface. It selects nodes
+// based off the list ordering from Nomad and is the default selector.
+type oldestCreateIndexClusterScaleInNodeSelector struct{}
+
+// newoldestCreateIndexClusterScaleInNodeSelector returns a new
+// oldestCreateIndexClusterScaleInNodeSelector implementation of the
+// ClusterScaleInNodeSelector interface.
+func newOldestCreateIndexClusterScaleInNodeSelector() ClusterScaleInNodeSelector {
+	return &oldestCreateIndexClusterScaleInNodeSelector{}
+}
+
+// Name satisfies the Name function on the ClusterScaleInNodeSelector
+// interface.
+func (n *oldestCreateIndexClusterScaleInNodeSelector) Name() string {
+	return sdk.TargetNodeSelectorStrategyOldestCreateIndex
+}
+
+// Select satisfies the Select function on the ClusterScaleInNodeSelector
+// interface.
+func (n *oldestCreateIndexClusterScaleInNodeSelector) Select(nodes []*api.NodeListStub, num int) []*api.NodeListStub {
+
+	last_index := len(nodes) - 1
+	if len(nodes) < num {
+		num = len(nodes)
+	}
+	out := make([]*api.NodeListStub, num)
+
+	for i := num - 1; i >= 0; i-- {
+		out[i] = nodes[(last_index)-i]
+	}
+	return out
+}

sdk/helper/scaleutils/nodeselector/oldest_create_index_test.go

@@ -0,0 +1,56 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package nodeselector
+
+import (
+	"testing"
+
+	"github.com/hashicorp/nomad/api"
+	"github.com/shoenig/test/must"
+)
+
+func Test_oldestClusterScaleInNodeSelectorName(t *testing.T) {
+	must.Eq(t, "oldest_create_index", newOldestCreateIndexClusterScaleInNodeSelector().Name())
+}
+
+func Test_oldestClusterScaleInNodeSelector_Select(t *testing.T) {
+	testCases := []struct {
+		inputNodes     []*api.NodeListStub
+		inputNum       int
+		expectedOutput []*api.NodeListStub
+		name           string
+	}{
+		{
+			inputNodes: []*api.NodeListStub{
+				{ID: "8d01d8fe-3c6b-0fdd-ebbc-a8b5cbb9c00c"},
+				{ID: "a6604683-fd65-c913-77ee-a0a15b8e88e9"},
+			},
+			inputNum: 1,
+			expectedOutput: []*api.NodeListStub{
+				{ID: "a6604683-fd65-c913-77ee-a0a15b8e88e9"},
+			},
+			name: "single selection needed",
+		},
+
+		{
+			inputNodes: []*api.NodeListStub{
+				{ID: "8d01d8fe-3c6b-0fdd-ebbc-a8b5cbb9c00c"},
+				{ID: "a6604683-fd65-c913-77ee-a0a15b8e88e9"},
+			},
+			inputNum: 3,
+			expectedOutput: []*api.NodeListStub{
+				{ID: "a6604683-fd65-c913-77ee-a0a15b8e88e9"},
+				{ID: "8d01d8fe-3c6b-0fdd-ebbc-a8b5cbb9c00c"},
+			},
+			name: "multiple selection",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			actualOutput := newOldestCreateIndexClusterScaleInNodeSelector().Select(tc.inputNodes, tc.inputNum)
+			must.Eq(t, tc.expectedOutput, actualOutput)
+		})
+	}
+}

sdk/helper/scaleutils/nodeselector/selector.go

@@ -49,6 +49,8 @@ func NewSelector(cfg map[string]string, client *api.Client, log hclog.Logger) (C
 		return newEmptyClusterScaleInNodeSelector(client, log, false), nil
 	case sdk.TargetNodeSelectorStrategyEmptyIgnoreSystemJobs:
 		return newEmptyClusterScaleInNodeSelector(client, log, true), nil
+	case sdk.TargetNodeSelectorStrategyOldestCreateIndex:
+		return newOldestCreateIndexClusterScaleInNodeSelector(), nil
 	default:
 		return nil, fmt.Errorf("unsupported node selector strategy: %v", val)
 	}

sdk/target.go

@@ -124,6 +124,10 @@ const (
 	// node selection strategy that only picks nodes without non-terminal
 	// allocations, without considering system jobs.
 	TargetNodeSelectorStrategyEmptyIgnoreSystemJobs = "empty_ignore_system"
+
+	// TargetNodeSelectorStrategyEmptyIgnoreSystemJobs is the cluster scale-in
+	// node selection strategy that picks the oldest running nodes
+	TargetNodeSelectorStrategyOldestCreateIndex = "oldest_create_index"
 )
 
 // TargetConfigConflictingClusterParams is a list containing horizontal cluster