feat(aggregators.final): Allow to specify output strategy

plugins/aggregators/final/README.md

@@ -29,12 +29,35 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
   period = "30s"
   ## If true, the original metric will be dropped by the
   ## aggregator and will not get sent to the output plugins.
-  drop_original = false
+  # drop_original = false
 
   ## The time that a series is not updated until considering it final.
-  series_timeout = "5m"
+  # series_timeout = "5m"
+
+  ## Output strategy, supported values:
+  ##   timeout  -- output a metric if no new input arrived for `series_timeout`;
+  ##               useful for filling gaps in input data
+  ##   periodic -- ouput the last received metric every `period`; useful to
+  ##               downsample the input data
+  # output_strategy = "timeout"
 ```
 
+### Output strategy
+
+By default (`output_strategy = "timeout"`) the plugin will only emit a metric
+for the period if the last received one is older than the series_timeout. This
+will not guarantee a regular output of a `final` metric e.g. if the
+series-timeout is a multiple of the gathering interval for an input. In this
+case metric sporadically arrive in the timeout phase of the period and emitting
+the `final` metric is surpressed.
+This can be helpful to fill in gaps in the data if no input arrived in time.
+
+Contrary to this, `output_strategy = "periodic"` will always output a `final`
+metric at the end of the period irrespectively of when the last metric arrived,
+the `series_timout` is ignored.
+This is helpful if you for example want to downsample input data arriving at a
+high rate and require a periodic output of the `final` metric.
+
 ## Metrics
 
 Measurement and tags are unchanged, fields are emitted with the suffix

plugins/aggregators/final/final.go

@@ -3,6 +3,7 @@ package final
 
 import (
 	_ "embed"
+	"fmt"
 	"time"
 
 	"github.com/influxdata/telegraf"
@@ -14,7 +15,8 @@ import (
 var sampleConfig string
 
 type Final struct {
-	SeriesTimeout config.Duration `toml:"series_timeout"`
+	OutputStrategy string          `toml:"output_strategy"`
+	SeriesTimeout  config.Duration `toml:"series_timeout"`
 
 	// The last metric for all series which are active
 	metricCache map[uint64]telegraf.Metric
@@ -23,14 +25,30 @@ type Final struct {
 func NewFinal() *Final {
 	return &Final{
 		SeriesTimeout: config.Duration(5 * time.Minute),
-		metricCache:   make(map[uint64]telegraf.Metric),
 	}
 }
 
 func (*Final) SampleConfig() string {
 	return sampleConfig
 }
 
+func (m *Final) Init() error {
+	// Check options and set defaults
+	switch m.OutputStrategy {
+	case "":
+		m.OutputStrategy = "timeout"
+	case "timeout", "periodic":
+		// Do nothing, those are valid
+	default:
+		return fmt.Errorf("invalid 'output_strategy': %q", m.OutputStrategy)
+	}
+
+	// Initialize the cache
+	m.metricCache = make(map[uint64]telegraf.Metric)
+
+	return nil
+}
+
 func (m *Final) Add(in telegraf.Metric) {
 	id := in.HashID()
 	m.metricCache[id] = in
@@ -41,14 +59,17 @@ func (m *Final) Push(acc telegraf.Accumulator) {
 	acc.SetPrecision(time.Nanosecond)
 
 	for id, metric := range m.metricCache {
-		if time.Since(metric.Time()) > time.Duration(m.SeriesTimeout) {
-			fields := map[string]interface{}{}
-			for _, field := range metric.FieldList() {
-				fields[field.Key+"_final"] = field.Value
-			}
-			acc.AddFields(metric.Name(), fields, metric.Tags(), metric.Time())
-			delete(m.metricCache, id)
+		if m.OutputStrategy == "timeout" && time.Since(metric.Time()) <= time.Duration(m.SeriesTimeout) {
+			// We output on timeout but the last metric of the series was
+			// younger than that. So skip the output for this period.
+			continue
+		}
+		fields := map[string]interface{}{}
+		for _, field := range metric.FieldList() {
+			fields[field.Key+"_final"] = field.Value
 		}
+		acc.AddFields(metric.Name(), fields, metric.Tags(), metric.Time())
+		delete(m.metricCache, id)
 	}
 }
 

plugins/aggregators/final/final_test.go

@@ -8,11 +8,13 @@ import (
 	"github.com/influxdata/telegraf/config"
 	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/testutil"
+	"github.com/stretchr/testify/require"
 )
 
 func TestSimple(t *testing.T) {
 	acc := testutil.Accumulator{}
 	final := NewFinal()
+	require.NoError(t, final.Init())
 
 	tags := map[string]string{"foo": "bar"}
 	m1 := metric.New("m1",
@@ -48,6 +50,7 @@ func TestSimple(t *testing.T) {
 func TestTwoTags(t *testing.T) {
 	acc := testutil.Accumulator{}
 	final := NewFinal()
+	require.NoError(t, final.Init())
 
 	tags1 := map[string]string{"foo": "bar"}
 	tags2 := map[string]string{"foo": "baz"}
@@ -94,6 +97,7 @@ func TestLongDifference(t *testing.T) {
 	acc := testutil.Accumulator{}
 	final := NewFinal()
 	final.SeriesTimeout = config.Duration(30 * time.Second)
+	require.NoError(t, final.Init())
 	tags := map[string]string{"foo": "bar"}
 
 	now := time.Now()
@@ -142,3 +146,129 @@ func TestLongDifference(t *testing.T) {
 	}
 	testutil.RequireMetricsEqual(t, expected, acc.GetTelegrafMetrics(), testutil.SortMetrics())
 }
+
+func TestOutputStrategyInvalid(t *testing.T) {
+	final := &Final{
+		OutputStrategy: "no way",
+		SeriesTimeout:  config.Duration(30 * time.Second),
+	}
+	require.ErrorContains(t, final.Init(), `invalid 'output_strategy'`)
+}
+
+func TestOutputStrategyTimeout(t *testing.T) {
+	final := &Final{
+		OutputStrategy: "timeout",
+		SeriesTimeout:  config.Duration(30 * time.Second),
+	}
+	require.NoError(t, final.Init())
+
+	now := time.Now()
+	tags := map[string]string{"foo": "bar"}
+	m1 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(1)},
+		now.Add(time.Second*-290))
+	m2 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(2)},
+		now.Add(time.Second*-275))
+	m3 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(3)},
+		now.Add(time.Second*-100))
+	m4 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(4)},
+		now.Add(time.Second*-20))
+
+	var acc testutil.Accumulator
+	final.Add(m1)
+	final.Add(m2)
+	final.Push(&acc)
+	final.Add(m3)
+	final.Push(&acc)
+	final.Add(m4)
+	final.Push(&acc)
+
+	expected := []telegraf.Metric{
+		testutil.MustMetric(
+			"m",
+			tags,
+			map[string]interface{}{
+				"a_final": 2,
+			},
+			now.Add(time.Second*-275),
+		),
+		testutil.MustMetric(
+			"m",
+			tags,
+			map[string]interface{}{
+				"a_final": 3,
+			},
+			now.Add(time.Second*-100),
+		),
+	}
+	testutil.RequireMetricsEqual(t, expected, acc.GetTelegrafMetrics(), testutil.SortMetrics())
+}
+
+func TestOutputStrategyPeriodic(t *testing.T) {
+	final := &Final{
+		OutputStrategy: "periodic",
+		SeriesTimeout:  config.Duration(30 * time.Second),
+	}
+	require.NoError(t, final.Init())
+
+	now := time.Now()
+	tags := map[string]string{"foo": "bar"}
+	m1 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(1)},
+		now.Add(time.Second*-290))
+	m2 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(2)},
+		now.Add(time.Second*-275))
+	m3 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(3)},
+		now.Add(time.Second*-100))
+	m4 := metric.New("m",
+		tags,
+		map[string]interface{}{"a": int64(4)},
+		now.Add(time.Second*-20))
+
+	var acc testutil.Accumulator
+	final.Add(m1)
+	final.Add(m2)
+	final.Push(&acc)
+	final.Add(m3)
+	final.Push(&acc)
+	final.Add(m4)
+	final.Push(&acc)
+
+	expected := []telegraf.Metric{
+		metric.New(
+			"m",
+			tags,
+			map[string]interface{}{
+				"a_final": 2,
+			},
+			now.Add(time.Second*-275),
+		),
+		metric.New(
+			"m",
+			tags,
+			map[string]interface{}{
+				"a_final": 3,
+			},
+			now.Add(time.Second*-100),
+		),
+		metric.New(
+			"m",
+			tags,
+			map[string]interface{}{"a_final": int64(4)},
+			now.Add(time.Second*-20),
+		),
+	}
+	testutil.RequireMetricsEqual(t, expected, acc.GetTelegrafMetrics(), testutil.SortMetrics())
+}

plugins/aggregators/final/sample.conf

@@ -4,7 +4,14 @@
   period = "30s"
   ## If true, the original metric will be dropped by the
   ## aggregator and will not get sent to the output plugins.
-  drop_original = false
+  # drop_original = false
 
   ## The time that a series is not updated until considering it final.
-  series_timeout = "5m"
+  # series_timeout = "5m"
+
+  ## Output strategy, supported values:
+  ##   timeout  -- output a metric if no new input arrived for `series_timeout`;
+  ##               useful for filling gaps in input data
+  ##   periodic -- ouput the last received metric every `period`; useful to
+  ##               downsample the input data
+  # output_strategy = "timeout"