Loki Write: Internal Labels

This change is to add logic so that labels that start with `__` are
filtered out, unless they are `externalLabels`. Labels that start with
`__` are used internally for things such as metadata. If a user want to
preserve the contents of one of these internal labels, then can do so
using relabelling to remove the `__`.

This change also adds tests which check various different scenarios

Author: matt-gp

CHANGELOG.md

@@ -68,6 +68,8 @@ Main (unreleased)
 
 - Only log EOF errors for syslog port investigations in `loki.source.syslog` as Debug, not Warn. (@dehaansa)
 
+- Fix `loki.write` no longer includes internal labels `__`.  (@matt-gp)
+
 v1.11.3
 -----------------
 

internal/component/common/loki/client/batch.go

@@ -66,7 +66,7 @@ func (b *batch) add(entry loki.Entry) error {
 	b.totalBytes += entrySize(entry.Entry)
 
 	// Append the entry to an already existing stream (if any)
-	labels := labelsMapToString(entry.Labels, ReservedLabelTenantID)
+	labels := labelsMapToString(entry.Labels)
 	if stream, ok := b.streams[labels]; ok {
 		stream.Entries = append(stream.Entries, entry.Entry)
 		return nil
@@ -90,7 +90,7 @@ func (b *batch) addFromWAL(lbs model.LabelSet, entry push.Entry, segmentNum int)
 	b.totalBytes += len(entry.Line)
 
 	// Append the entry to an already existing stream (if any)
-	labels := labelsMapToString(lbs, ReservedLabelTenantID)
+	labels := labelsMapToString(lbs)
 	if stream, ok := b.streams[labels]; ok {
 		stream.Entries = append(stream.Entries, entry)
 		b.countForSegment(segmentNum)
@@ -112,14 +112,16 @@ func (b *batch) addFromWAL(lbs model.LabelSet, entry push.Entry, segmentNum int)
 	return nil
 }
 
-// labelsMapToString encodes an entry's label set as a string, ignoring the without label.
-func labelsMapToString(ls model.LabelSet, without model.LabelName) string {
+// labelsMapToString encodes an entry's label set as a string, ignoring internal labels
+func labelsMapToString(ls model.LabelSet) string {
 	var b strings.Builder
 	totalSize := 2
 	lstrs := make([]model.LabelName, 0, len(ls))
 
 	for l, v := range ls {
-		if l == without {
+
+		// skip internal labels
+		if strings.HasPrefix(string(l), "__") {
 			continue
 		}
 

internal/component/common/loki/client/batch_test.go

@@ -180,7 +180,48 @@ func BenchmarkLabelsMapToString(b *testing.B) {
 	var r string
 	for i := 0; i < b.N; i++ {
 		// store in r prevent the compiler eliminating the function call.
-		r = labelsMapToString(labelSet, ReservedLabelTenantID)
+		r = labelsMapToString(labelSet)
 	}
 	result = r
 }
+
+func TestLabelsMapToString(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    model.LabelSet
+		expected string
+	}{
+		{
+			name:     "empty label set",
+			input:    model.LabelSet{},
+			expected: "{}",
+		},
+		{
+			name:     "single label",
+			input:    model.LabelSet{"app": "my-app"},
+			expected: `{app="my-app"}`,
+		},
+		{
+			name:     "multiple labels",
+			input:    model.LabelSet{"app": "my-app", "env": "prod"},
+			expected: `{app="my-app", env="prod"}`,
+		},
+		{
+			name:     "labels with reserved labels",
+			input:    model.LabelSet{"app": "my-app", "__meta_label_abc": "meta-abc", "__meta_label_def": "meta-def", "abc": "123"},
+			expected: `{abc="123", app="my-app"}`,
+		},
+		{
+			name:     "only reserved labels",
+			input:    model.LabelSet{"__meta_label_abc": "meta-abc", "__meta_label_def": "meta-def"},
+			expected: "{}",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			actual := labelsMapToString(tc.input)
+			assert.Equal(t, tc.expected, actual)
+		})
+	}
+}