prometheusremotewrite: Don't generate target_info unless at least one identifying label is defined (#32148)

**Description:** <Describe what has changed.>
I propose modifying the Prometheus remote write translator such that it
will only generate the `target_info` metric if at least one identifying
label is defined, i.e. either `job` or `instance` (or both). The
rationale is that without any identifying labels, `target_info` is
useless (you can't join against it).

See [Slack
thread](https://cloud-native.slack.com/archives/C01LSCJBXDZ/p1712161732017409)
for background.

**Testing:** <Describe what testing was performed and which tests were
added.>
I've modified the `addResourceTargetInfo` tests to reflect that at least
one identifying label is required, and added some new ones to cover the
different cases. I also modify a couple of
`prometheusremotewriteexporter` tests that are affected by this change,
as they don't define the identifying resource attributes.

**Documentation:** <Describe the documentation added.>

---------

Signed-off-by: Arve Knudsen <[email protected]>
Co-authored-by: Anthony Mirabella <[email protected]>

Author: aknuds1

.chloggen/bugfix_target-info-required-attrs.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusremotewrite
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Change prometheusremotewrite.FromMetrics so that the target_info metric is only generated if at least one identifying OTel resource attribute (service.name and/or service.instance.id) is defined.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32148]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

exporter/prometheusremotewriteexporter/exporter_test.go

@@ -497,7 +497,7 @@ func Test_PushMetrics(t *testing.T) {
 			name:               "intSum_case",
 			metrics:            intSumBatch,
 			reqTestFunc:        checkFunc,
-			expectedTimeSeries: 5,
+			expectedTimeSeries: 4,
 			httpResponseCode:   http.StatusAccepted,
 		},
 		{

pkg/translator/prometheusremotewrite/helper.go

@@ -540,6 +540,19 @@ func addResourceTargetInfo(resource pcommon.Resource, settings Settings, timesta
 	}
 
 	labels := createAttributes(resource, attributes, settings.ExternalLabels, identifyingAttrs, false, model.MetricNameLabel, name)
+	haveIdentifier := false
+	for _, l := range labels {
+		if l.Name == model.JobLabel || l.Name == model.InstanceLabel {
+			haveIdentifier = true
+			break
+		}
+	}
+
+	if !haveIdentifier {
+		// We need at least one identifying label to generate target_info.
+		return
+	}
+
 	sample := &prompb.Sample{
 		Value: float64(1),
 		// convert ns to ms

pkg/translator/prometheusremotewrite/helper_test.go

@@ -4,7 +4,6 @@
 package prometheusremotewrite
 
 import (
-	"fmt"
 	"math"
 	"sort"
 	"testing"
@@ -532,10 +531,18 @@ func TestAddResourceTargetInfo(t *testing.T) {
 		conventions.AttributeServiceInstanceID: "service-instance-id",
 	}
 	resourceWithServiceAttrs := pcommon.NewResource()
-	assert.NoError(t, resourceWithServiceAttrs.Attributes().FromRaw(resourceAttrMap))
+	require.NoError(t, resourceWithServiceAttrs.Attributes().FromRaw(resourceAttrMap))
 	resourceWithServiceAttrs.Attributes().PutStr("resource_attr", "resource-attr-val-1")
 	resourceWithOnlyServiceAttrs := pcommon.NewResource()
-	assert.NoError(t, resourceWithOnlyServiceAttrs.Attributes().FromRaw(resourceAttrMap))
+	require.NoError(t, resourceWithOnlyServiceAttrs.Attributes().FromRaw(resourceAttrMap))
+	// service.name is an identifying resource attribute.
+	resourceWithOnlyServiceName := pcommon.NewResource()
+	resourceWithOnlyServiceName.Attributes().PutStr(conventions.AttributeServiceName, "service-name")
+	resourceWithOnlyServiceName.Attributes().PutStr("resource_attr", "resource-attr-val-1")
+	// service.instance.id is an identifying resource attribute.
+	resourceWithOnlyServiceID := pcommon.NewResource()
+	resourceWithOnlyServiceID.Attributes().PutStr(conventions.AttributeServiceInstanceID, "service-instance-id")
+	resourceWithOnlyServiceID.Attributes().PutStr("resource_attr", "resource-attr-val-1")
 	for _, tc := range []struct {
 		desc       string
 		resource   pcommon.Resource
@@ -549,61 +556,54 @@ func TestAddResourceTargetInfo(t *testing.T) {
 		},
 		{
 			desc:     "disable target info metric",
-			resource: testdata.GenerateMetricsNoLibraries().ResourceMetrics().At(0).Resource(),
+			resource: resourceWithOnlyServiceName,
 			settings: Settings{DisableTargetInfo: true},
 		},
 		{
-			desc:      "with resource",
+			desc:      "with resource missing both service.name and service.instance.id resource attributes",
 			resource:  testdata.GenerateMetricsNoLibraries().ResourceMetrics().At(0).Resource(),
 			timestamp: testdata.TestMetricStartTimestamp,
+		},
+		{
+			desc:      "with resource including service.instance.id, and missing service.name resource attribute",
+			resource:  resourceWithOnlyServiceID,
+			timestamp: testdata.TestMetricStartTimestamp,
 			wantLabels: []prompb.Label{
-				{
-					Name:  model.MetricNameLabel,
-					Value: targetMetricName,
-				},
-				{
-					Name:  "resource_attr",
-					Value: "resource-attr-val-1",
-				},
+				{Name: model.MetricNameLabel, Value: "target_info"},
+				{Name: model.InstanceLabel, Value: "service-instance-id"},
+				{Name: "resource_attr", Value: "resource-attr-val-1"},
 			},
 		},
 		{
-			desc:      "with resource, with namespace",
-			resource:  testdata.GenerateMetricsNoLibraries().ResourceMetrics().At(0).Resource(),
+			desc:      "with resource including service.name, and missing service.instance.id resource attribute",
+			resource:  resourceWithOnlyServiceName,
+			timestamp: testdata.TestMetricStartTimestamp,
+			wantLabels: []prompb.Label{
+				{Name: model.MetricNameLabel, Value: "target_info"},
+				{Name: model.JobLabel, Value: "service-name"},
+				{Name: "resource_attr", Value: "resource-attr-val-1"},
+			},
+		},
+		{
+			desc:      "with valid resource, with namespace",
+			resource:  resourceWithOnlyServiceName,
 			timestamp: testdata.TestMetricStartTimestamp,
 			settings:  Settings{Namespace: "foo"},
 			wantLabels: []prompb.Label{
-				{
-					Name:  model.MetricNameLabel,
-					Value: fmt.Sprintf("foo_%s", targetMetricName),
-				},
-				{
-					Name:  "resource_attr",
-					Value: "resource-attr-val-1",
-				},
+				{Name: model.MetricNameLabel, Value: "foo_target_info"},
+				{Name: model.JobLabel, Value: "service-name"},
+				{Name: "resource_attr", Value: "resource-attr-val-1"},
 			},
 		},
 		{
 			desc:      "with resource, with service attributes",
 			resource:  resourceWithServiceAttrs,
 			timestamp: testdata.TestMetricStartTimestamp,
 			wantLabels: []prompb.Label{
-				{
-					Name:  model.MetricNameLabel,
-					Value: targetMetricName,
-				},
-				{
-					Name:  "instance",
-					Value: "service-instance-id",
-				},
-				{
-					Name:  "job",
-					Value: "service-namespace/service-name",
-				},
-				{
-					Name:  "resource_attr",
-					Value: "resource-attr-val-1",
-				},
+				{Name: model.MetricNameLabel, Value: "target_info"},
+				{Name: model.InstanceLabel, Value: "service-instance-id"},
+				{Name: model.JobLabel, Value: "service-namespace/service-name"},
+				{Name: "resource_attr", Value: "resource-attr-val-1"},
 			},
 		},
 		{