prometheusremotewrite: Don't generate target_info unless there are me…

…trics (open-telemetry#32318)

**Description:** <Describe what has changed.>
Modify `prometheusremotewrite.FromMetrics` to not generate `target_info`
unless there are metrics, as you can't detect a timestamp otherwise.
Currently, if there are no metrics, a `target_info` metric is generated
with the Unix epoch for timestamp.

**Link to tracking Issue:** <Issue number if applicable>
See Mimir [issue](grafana/mimir#7272) where
this was reported.

**Testing:**
I've added a test case for the bug.

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

---------

Signed-off-by: Arve Knudsen <[email protected]>
Co-authored-by: David Ashpole <[email protected]>

.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]

exporter/prometheusremotewriteexporter/exporter_test.go

@@ -490,7 +490,7 @@ func Test_PushMetrics(t *testing.T) {
  metrics: invalidTypeBatch,
  httpResponseCode: http.StatusAccepted,
  reqTestFunc: checkFunc,
- expectedTimeSeries: 1, // the resource target metric.
+ expectedTimeSeries: 0,
  expectedFailedTranslations: 1,
  },
  {

pkg/translator/prometheusremotewrite/helper.go

@@ -512,7 +512,7 @@ func (c *prometheusConverter) addTimeSeriesIfNeeded(lbls []prompb.Label, startTi
 
 // addResourceTargetInfo converts the resource to the target info metric.
 func addResourceTargetInfo(resource pcommon.Resource, settings Settings, timestamp pcommon.Timestamp, converter *prometheusConverter) {
- if settings.DisableTargetInfo {
+ if settings.DisableTargetInfo || timestamp == 0 {
  return
  }
 

pkg/translator/prometheusremotewrite/helper_test.go

@@ -611,6 +611,12 @@ func TestAddResourceTargetInfo(t *testing.T) {
  resource: resourceWithOnlyServiceAttrs,
  timestamp: testdata.TestMetricStartTimestamp,
  },
+ {
+ // 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,
+ },
  } {
  t.Run(tc.desc, func(t *testing.T) {
  converter := newPrometheusConverter()