[CASCL-1386] (6/11) Extract shared EC2 instance-ID helper to common/aws (#3173)

* [CASCL-1386] Add evict-legacy-nodes command skeleton

Part of a stack splitting #3026 (too large to review in one piece) into
small pieces that each build and pass tests on their own. The command is
fully functional only once the whole stack lands.

* [CASCL-1386] Implement evict-legacy-nodes execution plan building

Part of a stack splitting #3026 (too large to review in one piece) into
small pieces that each build and pass tests on their own. The command is
fully functional only once the whole stack lands.

* [CASCL-1386] Implement evict-legacy-nodes plan display and confirmation

Part of a stack splitting #3026 (too large to review in one piece) into
small pieces that each build and pass tests on their own. The command is
fully functional only once the whole stack lands.

* [CASCL-1386] Implement evict-legacy-nodes preflight warnings

Part of a stack splitting #3026 (too large to review in one piece) into
small pieces that each build and pass tests on their own. The command is
fully functional only once the whole stack lands.

* [CASCL-1386] Implement cluster-autoscaler scale-down for evict-legacy-nodes

Part of a stack splitting #3026 (too large to review in one piece) into
small pieces that each build and pass tests on their own. The command is
fully functional only once the whole stack lands.

* [CASCL-1386] Extract shared EC2 instance-ID helper to common/aws

Part of a stack splitting #3026 (too large to review in one piece) into
small pieces that each build and pass tests on their own. The command is
fully functional only once the whole stack lands.

Author: L3n41c

cmd/kubectl-datadog/autoscaling/cluster/common/aws/node.go

@@ -0,0 +1,36 @@
+package aws
+
+import (
+	"regexp"
+
+	corev1 "k8s.io/api/core/v1"
+)
+
+// awsProviderIDRegexp matches the AWS provider ID for EC2-backed nodes.
+// Format: aws:///<az>/i-<hex> (e.g. aws:///us-east-1a/i-0abc123def456789).
+// Fargate nodes use a different shape (aws:///<az>/fargate-ip-...) and must
+// therefore be classified by label before reaching this regex.
+var awsProviderIDRegexp = regexp.MustCompile(`^aws:///[^/]+/(i-[0-9a-f]+)$`)
+
+// LabelEKSNodegroup is the label EKS stamps on every node that belongs to a
+// managed node group. The label value is the node group name. Exposed as a
+// constant so every consumer (classifier, evict-legacy-nodes, future code)
+// references the same string.
+const LabelEKSNodegroup = "eks.amazonaws.com/nodegroup"
+
+// ExtractEC2InstanceID returns the EC2 instance ID (i-...) from a Node's
+// providerID, or false when the providerID is not an EC2 instance (Fargate
+// uses `aws:///<az>/fargate-ip-...`, GCP/Azure use entirely different shapes,
+// etc.). Lives here in `common/aws` so both `common/clusterinfo` (which
+// imports `common/karpenter`) and `common/karpenter` (which classifies its
+// own nodes) can use it without creating an import cycle.
+func ExtractEC2InstanceID(node *corev1.Node) (string, bool) {
+	if node == nil {
+		return "", false
+	}
+	m := awsProviderIDRegexp.FindStringSubmatch(node.Spec.ProviderID)
+	if len(m) != 2 {
+		return "", false
+	}
+	return m[1], true
+}

cmd/kubectl-datadog/autoscaling/cluster/common/aws/node_test.go

@@ -0,0 +1,38 @@
+package aws
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	corev1 "k8s.io/api/core/v1"
+)
+
+func TestExtractEC2InstanceID(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		provider string
+		wantID   string
+		wantOK   bool
+	}{
+		{name: "ec2", provider: "aws:///eu-west-3a/i-0123456789abcdef0", wantID: "i-0123456789abcdef0", wantOK: true},
+		{name: "ec2 short id", provider: "aws:///us-east-1b/i-abc123", wantID: "i-abc123", wantOK: true},
+		{name: "fargate", provider: "aws:///eu-west-3a/fargate-ip-10-0-1-2", wantOK: false},
+		{name: "gcp", provider: "gce://project/zone/instance", wantOK: false},
+		{name: "empty", provider: "", wantOK: false},
+		{name: "missing prefix", provider: "i-0123456789abcdef0", wantOK: false},
+		{name: "missing AZ", provider: "aws:////i-0123456789abcdef0", wantOK: false},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			node := &corev1.Node{Spec: corev1.NodeSpec{ProviderID: tc.provider}}
+			id, ok := ExtractEC2InstanceID(node)
+			assert.Equal(t, tc.wantOK, ok)
+			if tc.wantOK {
+				assert.Equal(t, tc.wantID, id)
+			}
+		})
+	}
+	t.Run("nil node", func(t *testing.T) {
+		_, ok := ExtractEC2InstanceID(nil)
+		assert.False(t, ok)
+	})
+}

cmd/kubectl-datadog/autoscaling/cluster/common/clusterinfo/classify.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"log"
 	"maps"
-	"regexp"
 	"strings"
 	"time"
 
@@ -36,11 +35,6 @@ import (
 // ValidationError at the API.
 const describeASGInstancesMaxIDs = 50
 
-// awsProviderIDRegexp matches the AWS provider ID for EC2-backed nodes.
-// Format: aws:///<az>/i-<hex>. Fargate nodes use a different shape and
-// must therefore be classified by label before reaching this regex.
-var awsProviderIDRegexp = regexp.MustCompile(`^aws:///[^/]+/(i-[0-9a-f]+)$`)
-
 // nodePoolDatadogCreatedLabel is the label set by every Datadog autoscaling
 // product (kubectl-datadog AND the cluster agent) on the NodePools they
 // manage. Broader than the AND-pair `app.kubernetes.io/managed-by:
@@ -173,10 +167,9 @@ func classifyByLabels(ctx context.Context, k8sClient kubernetes.Interface, farga
 			return nil
 		}
 
-		matches := awsProviderIDRegexp.FindStringSubmatch(node.Spec.ProviderID)
-		if len(matches) == 2 {
+		if id, ok := commonaws.ExtractEC2InstanceID(node); ok {
 			candidates = append(candidates, asgCandidate{
-				instanceID: matches[1],
+				instanceID: id,
 				nodeName:   node.Name,
 			})
 		} else {

cmd/kubectl-datadog/autoscaling/cluster/common/karpenter/fromnodes.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"log"
 	"maps"
-	"regexp"
 	"slices"
 	"strings"
 
@@ -17,11 +16,9 @@ import (
 	"k8s.io/apimachinery/pkg/runtime"
 	"k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/tools/pager"
-)
 
-// awsProviderIDRegexp matches the AWS provider ID format for EC2 instances.
-// Format: aws:///ZONE/INSTANCE_ID (e.g., aws:///us-east-1a/i-0abc123def456789)
-var awsProviderIDRegexp = regexp.MustCompile(`^aws:///[^/]+/(i-[0-9a-f]+)$`)
+	commonaws "github.com/DataDog/datadog-operator/cmd/kubectl-datadog/autoscaling/cluster/common/aws"
+)
 
 // ec2DescribeBatchSize bounds the number of instance IDs we hand to a single
 // ec2:DescribeInstances / ec2:DescribeImages call. The K8s pager streams
@@ -62,12 +59,12 @@ func GetNodesProperties(ctx context.Context, clientset *kubernetes.Clientset, ec
 		if _, isKarpenter := node.Labels["karpenter.k8s.aws/ec2nodeclass"]; isKarpenter {
 			return nil
 		}
-		matches := awsProviderIDRegexp.FindStringSubmatch(node.Spec.ProviderID)
-		if len(matches) != 2 {
+		id, ok := commonaws.ExtractEC2InstanceID(node)
+		if !ok {
 			log.Printf("Skipping node %s with unexpected provider ID: %s", node.Name, node.Spec.ProviderID)
 			return nil
 		}
-		pending[matches[1]] = pendingNode{labels: node.Labels, taints: node.Spec.Taints}
+		pending[id] = pendingNode{labels: node.Labels, taints: node.Spec.Taints}
 		if len(pending) >= ec2DescribeBatchSize {
 			return flush()
 		}