feat(gfd): make labeler composition fault-tolerant

Make Merge() resilient to individual labeler failures by logging errors
as warnings and continuing with remaining labelers. This prevents GFD
from crashing when devices go unhealthy (e.g., XID errors) and allows
partial label generation.

Signed-off-by: Carlos Eduardo Arango Gutierrez <[email protected]>

Author: ArangoGutierrez

internal/lm/list.go

@@ -16,7 +16,9 @@
 
 package lm
 
-import "fmt"
+import (
+	"k8s.io/klog/v2"
+)
 
 // list represents a list of labelers that iself implements the Labeler interface.
 type list []Labeler
@@ -29,13 +31,17 @@ func Merge(labelers ...Labeler) Labeler {
 }
 
 // Labels returns the labels from a set of labelers. Labels later in the list
-// overwrite earlier labels.
+// overwrite earlier labels. If a labeler fails, the error is logged as a
+// warning and the labeler is skipped, allowing the pipeline to continue with
+// partial results. This provides fault tolerance for unhealthy devices or
+// transient errors without crashing the entire labeling process.
 func (labelers list) Labels() (Labels, error) {
 	allLabels := make(Labels)
-	for _, labeler := range labelers {
+	for i, labeler := range labelers {
 		labels, err := labeler.Labels()
 		if err != nil {
-			return nil, fmt.Errorf("error generating labels: %v", err)
+			klog.Warningf("Labeler at index %d failed, skipping: %v", i, err)
+			continue
 		}
 		for k, v := range labels {
 			allLabels[k] = v

internal/lm/list_test.go

@@ -0,0 +1,141 @@
+/**
+# Copyright (c) 2025, NVIDIA CORPORATION.  All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+**/
+
+package lm
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// mockLabeler is a test double for the Labeler interface
+type mockLabeler struct {
+	labels Labels
+	err    error
+}
+
+func (m *mockLabeler) Labels() (Labels, error) {
+	return m.labels, m.err
+}
+
+func TestMerge(t *testing.T) {
+	testCases := []struct {
+		description    string
+		labelers       []Labeler
+		expectedLabels Labels
+	}{
+		{
+			description:    "empty list returns empty labels",
+			labelers:       []Labeler{},
+			expectedLabels: Labels{},
+		},
+		{
+			description: "single successful labeler",
+			labelers: []Labeler{
+				&mockLabeler{
+					labels: Labels{"key1": "value1"},
+				},
+			},
+			expectedLabels: Labels{"key1": "value1"},
+		},
+		{
+			description: "multiple successful labelers",
+			labelers: []Labeler{
+				&mockLabeler{labels: Labels{"key1": "value1"}},
+				&mockLabeler{labels: Labels{"key2": "value2"}},
+				&mockLabeler{labels: Labels{"key3": "value3"}},
+			},
+			expectedLabels: Labels{
+				"key1": "value1",
+				"key2": "value2",
+				"key3": "value3",
+			},
+		},
+		{
+			description: "single failing labeler is skipped",
+			labelers: []Labeler{
+				&mockLabeler{labels: Labels{"key1": "value1"}},
+				&mockLabeler{err: fmt.Errorf("device unhealthy: GPU is lost")},
+				&mockLabeler{labels: Labels{"key3": "value3"}},
+			},
+			expectedLabels: Labels{
+				"key1": "value1",
+				"key3": "value3",
+			},
+		},
+		{
+			description: "multiple failing labelers are skipped",
+			labelers: []Labeler{
+				&mockLabeler{labels: Labels{"key1": "value1"}},
+				&mockLabeler{err: fmt.Errorf("error 1")},
+				&mockLabeler{err: fmt.Errorf("error 2")},
+				&mockLabeler{labels: Labels{"key4": "value4"}},
+			},
+			expectedLabels: Labels{
+				"key1": "value1",
+				"key4": "value4",
+			},
+		},
+		{
+			description: "all failing labelers returns empty labels",
+			labelers: []Labeler{
+				&mockLabeler{err: fmt.Errorf("error 1")},
+				&mockLabeler{err: fmt.Errorf("error 2")},
+			},
+			expectedLabels: Labels{},
+		},
+		{
+			description: "later labeler overwrites earlier labels",
+			labelers: []Labeler{
+				&mockLabeler{labels: Labels{"key": "value1"}},
+				&mockLabeler{labels: Labels{"key": "value2"}},
+			},
+			expectedLabels: Labels{"key": "value2"},
+		},
+		{
+			description: "empty labels from labeler are merged",
+			labelers: []Labeler{
+				&mockLabeler{labels: Labels{}},
+				&mockLabeler{labels: Labels{"key": "value"}},
+			},
+			expectedLabels: Labels{"key": "value"},
+		},
+		{
+			description: "failing labeler between successful ones",
+			labelers: []Labeler{
+				&mockLabeler{labels: Labels{"before": "value"}},
+				&mockLabeler{err: fmt.Errorf("GPU XID error")},
+				&mockLabeler{labels: Labels{"after": "value"}},
+			},
+			expectedLabels: Labels{
+				"before": "value",
+				"after":  "value",
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.description, func(t *testing.T) {
+			merged := Merge(tc.labelers...)
+			labels, err := merged.Labels()
+
+			require.NoError(t, err, "Merge should never return error")
+			require.EqualValues(t, tc.expectedLabels, labels)
+		})
+	}
+}