feat(agent): Add option to avoid filtering of explicit plugin tags (#13364)

config/config.go

@@ -252,6 +252,10 @@ type AgentConfig struct {
 	// stateful plugins on termination of Telegraf. If the file exists on start,
 	// the state in the file will be restored for the plugins.
 	Statefile string `toml:"statefile"`
+
+	// Flag to always keep tags explicitly defined in the plugin itself and
+	// ensure those tags always pass filtering.
+	AlwaysIncludeLocalTags bool `toml:"always_include_local_tags"`
 }
 
 // InputNames returns a list of strings of the configured inputs.
@@ -1428,7 +1432,10 @@ func (c *Config) buildFilter(tbl *ast.Table) (models.Filter, error) {
 // builds the filter and returns a
 // models.InputConfig to be inserted into models.RunningInput
 func (c *Config) buildInput(name string, tbl *ast.Table) (*models.InputConfig, error) {
-	cp := &models.InputConfig{Name: name}
+	cp := &models.InputConfig{
+		Name:                   name,
+		AlwaysIncludeLocalTags: c.Agent.AlwaysIncludeLocalTags,
+	}
 	c.getFieldDuration(tbl, "interval", &cp.Interval)
 	c.getFieldDuration(tbl, "precision", &cp.Precision)
 	c.getFieldDuration(tbl, "collection_jitter", &cp.CollectionJitter)
@@ -1523,7 +1530,7 @@ func (c *Config) buildOutput(name string, tbl *ast.Table) (*models.OutputConfig,
 func (c *Config) missingTomlField(_ reflect.Type, key string) error {
 	switch key {
 	// General options to ignore
-	case "alias",
+	case "alias", "always_include_local_tags",
 		"collection_jitter", "collection_offset",
 		"data_format", "delay", "drop", "drop_original",
 		"fielddrop", "fieldpass", "flush_interval", "flush_jitter",

docs/CONFIGURATION.md

@@ -321,6 +321,11 @@ The agent table configures Telegraf and the defaults used across all plugins.
   stateful plugins on termination of Telegraf. If the file exists on start,
   the state in the file will be restored for the plugins.
 
+- **always_include_local_tags**:
+  Ensure tags explicitly defined in a plugin will *always* pass tag-filtering
+  via `taginclude` or `tagexclude`. This removes the need to specify local tags
+  twice.
+
 ## Plugins
 
 Telegraf plugins are divided into 4 types: [inputs][], [outputs][],
@@ -402,7 +407,7 @@ Use the name_override parameter to emit measurements with the name `foobar`:
 Emit measurements with two additional tags: `tag1=foo` and `tag2=bar`
 
 > **NOTE**: With TOML, order matters.  Parameters belong to the last defined
-> table header, place `[inputs.cpu.tags]` table at the _end_ of the plugin
+> table header, place `[inputs.cpu.tags]` table at the *end* of the plugin
 > definition.
 
 ```toml
@@ -638,7 +643,7 @@ for time-based filtering. An introduction to the CEL language can be found
 are provided in the [language definition][CEL lang] as well as in the
 [extension documentation][CEL ext].
 
-> NOTE: As CEL is an _interpreted_ languguage, this type of filtering is much
+> NOTE: As CEL is an *interpreted* languguage, this type of filtering is much
 > slower compared to `namepass`/`namedrop` and friends. So consider to use the
 > more restricted filter options where possible in case of high-throughput
 > scenarios.

models/running_input.go

@@ -69,6 +69,7 @@ type InputConfig struct {
 	MeasurementSuffix      string
 	Tags                   map[string]string
 	Filter                 Filter
+	AlwaysIncludeLocalTags bool
 }
 
 func (r *RunningInput) metricFiltered(metric telegraf.Metric) {
@@ -105,12 +106,17 @@ func (r *RunningInput) MakeMetric(metric telegraf.Metric) telegraf.Metric {
 		return nil
 	}
 
+	tags := r.Config.Tags
+	if r.Config.AlwaysIncludeLocalTags {
+		tags = nil
+	}
+
 	m := makemetric(
 		metric,
 		r.Config.NameOverride,
 		r.Config.MeasurementPrefix,
 		r.Config.MeasurementSuffix,
-		r.Config.Tags,
+		tags,
 		r.defaultTags)
 
 	r.Config.Filter.Modify(metric)
@@ -119,6 +125,15 @@ func (r *RunningInput) MakeMetric(metric telegraf.Metric) telegraf.Metric {
 		return nil
 	}
 
+	if r.Config.AlwaysIncludeLocalTags {
+		// Apply plugin tags after filtering
+		for k, v := range r.Config.Tags {
+			if _, ok := metric.GetTag(k); !ok {
+				metric.AddTag(k, v)
+			}
+		}
+	}
+
 	r.MetricsGathered.Incr(1)
 	GlobalMetricsGathered.Incr(1)
 	return m

models/running_input_test.go

@@ -273,6 +273,81 @@ func TestMetricErrorCounters(t *testing.T) {
 	require.GreaterOrEqual(t, int64(1), GlobalGatherErrors.Get())
 }
 
+func TestMakeMetricWithAlwaysKeepingPluginTagsDisabled(t *testing.T) {
+	now := time.Now()
+	ri := NewRunningInput(&testInput{}, &InputConfig{
+		Name: "TestRunningInput",
+		Tags: map[string]string{
+			"foo": "bar",
+		},
+		Filter: Filter{
+			TagInclude: []string{"b"},
+		},
+		AlwaysIncludeLocalTags: false,
+	})
+	require.NoError(t, ri.Config.Filter.Compile())
+
+	m := testutil.MustMetric("RITest",
+		map[string]string{
+			"b": "test",
+		},
+		map[string]interface{}{
+			"value": int64(101),
+		},
+		now,
+		telegraf.Untyped)
+	m = ri.MakeMetric(m)
+
+	expected := metric.New("RITest",
+		map[string]string{
+			"b": "test",
+		},
+		map[string]interface{}{
+			"value": 101,
+		},
+		now,
+	)
+	require.Equal(t, expected, m)
+}
+
+func TestMakeMetricWithAlwaysKeepingPluginTagsEnabled(t *testing.T) {
+	now := time.Now()
+	ri := NewRunningInput(&testInput{}, &InputConfig{
+		Name: "TestRunningInput",
+		Tags: map[string]string{
+			"foo": "bar",
+		},
+		Filter: Filter{
+			TagInclude: []string{"b"},
+		},
+		AlwaysIncludeLocalTags: true,
+	})
+	require.NoError(t, ri.Config.Filter.Compile())
+
+	m := testutil.MustMetric("RITest",
+		map[string]string{
+			"b": "test",
+		},
+		map[string]interface{}{
+			"value": int64(101),
+		},
+		now,
+		telegraf.Untyped)
+	m = ri.MakeMetric(m)
+
+	expected := metric.New("RITest",
+		map[string]string{
+			"b":   "test",
+			"foo": "bar",
+		},
+		map[string]interface{}{
+			"value": 101,
+		},
+		now,
+	)
+	require.Equal(t, expected, m)
+}
+
 type testInput struct{}
 
 func (t *testInput) Description() string                 { return "" }