prometheusremotewrite: Don't generate target_info if no metrics

Modify prometheusremotewrite.FromMetrics to not generate target_info
if there are no metrics, as you can't detect the most recent timestamp.
Currently, if there are no metrics, a target_info metric is generated
with the Unix epoch for timestamp.

Signed-off-by: Arve Knudsen <[email protected]>

Author: aknuds1

.chloggen/bugfix_missing-resource-timestamp.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: Modify prometheusremotewrite.FromMetrics to only generate target_info if there are metrics, as otherwise you can't deduce the timestamp.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [32318]
+
+# (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,api]

pkg/translator/prometheusremotewrite/helper.go

@@ -526,7 +526,7 @@ func addCreatedTimeSeriesIfNeeded(
 
 // addResourceTargetInfo converts the resource to the target info metric
 func addResourceTargetInfo(resource pcommon.Resource, settings Settings, timestamp pcommon.Timestamp, tsMap map[string]*prompb.TimeSeries) {
-	if settings.DisableTargetInfo {
+	if settings.DisableTargetInfo || timestamp == 0 {
 		return
 	}
 	// Use resource attributes (other than those used for job+instance) as the

pkg/translator/prometheusremotewrite/helper_test.go

@@ -622,6 +622,13 @@ func TestAddResourceTargetInfo(t *testing.T) {
 			timestamp: testdata.TestMetricStartTimestamp,
 			expected:  map[string]*prompb.TimeSeries{},
 		},
+		{
+			// If there's no timestamp, target_info shouldn't be generated, since we don't know when the write is from.
+			desc:      "with resource, with service attributes, without timestamp",
+			resource:  resourceWithServiceAttrs,
+			timestamp: 0,
+			expected:  map[string]*prompb.TimeSeries{},
+		},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
 			tsMap := map[string]*prompb.TimeSeries{}