conntrack: Add _IsFirst field

README.md

@@ -615,6 +615,7 @@ A possible output would look like:
 {
     "_RecordType": "endConnection",
     "_HashId": "3e8ba98164baecaf",
+    "_IsFirst": true,
     "SrcAddr": "10.0.0.1",
     "SrcPort": 1234,
     "DstAddr": "10.0.0.2",
@@ -646,6 +647,11 @@ Output fields that set `splitAB: true` (like in `Bytes`) are split into 2 fields
 aggregate values separately based on direction A->B and B->A respectively.
 When `splitAB` is absent, its default value is `false`.
 
+The boolean field `_IsFirst` exists only in records of type `newConnection`, `updateConnection` and `endConnection`.
+It is set to true only on the first record of the connection.
+The `_IsFirst` fields is useful in cases where `newConnection` records are not outputted (to reduce the number output records)
+and there is a need to count the total number of connections: simply counting `_IsFirst=true` 
+
 ### Timebased TopK
 
 It is sometimes desirable to return only a subset of records, such as those connections that use the most bandwidth.

pkg/api/conntrack.go

@@ -24,6 +24,7 @@ import (
 const (
 	HashIdFieldName     = "_HashId"
 	RecordTypeFieldName = "_RecordType"
+	IsFirstFieldName    = "_IsFirst"
 )
 
 type ConnTrack struct {

pkg/pipeline/conntrack_integ_test.go

@@ -138,6 +138,7 @@ func TestConnTrack(t *testing.T) {
 		"TimeFlowStart": 1_637_501_079.0,
 		"_HashId":       "d28db42bcd8aea8f",
 		"_RecordType":   "endConnection",
+		"_IsFirst":      false,
 		"numFlowLogs":   5.0,
 	}
 	// Wait for the record to be eventually forwarded to the writer

pkg/pipeline/extract/conntrack/conn.go

@@ -36,6 +36,10 @@ type connection interface {
 	getNextUpdateReportTime() time.Time
 	toGenericMap() config.GenericMap
 	getHash() totalHashType
+	// markReported marks the connection as has been reported. That is, at least one connection record has been emitted
+	// for this connection (i.e. newConnection, updateConnection, endConnection).
+	// It returns true on the first invocation to indicate the first report. Otherwise, it returns false.
+	markReported() bool
 }
 
 type connType struct {
@@ -44,6 +48,7 @@ type connType struct {
 	aggFields            map[string]float64
 	expiryTime           time.Time
 	nextUpdateReportTime time.Time
+	isReported           bool
 }
 
 func (c *connType) addAgg(fieldName string, initValue float64) {
@@ -95,15 +100,22 @@ func (c *connType) getHash() totalHashType {
 	return c.hash
 }
 
+func (c *connType) markReported() bool {
+	isFirst := !c.isReported
+	c.isReported = true
+	return isFirst
+}
+
 type connBuilder struct {
 	conn *connType
 }
 
 func NewConnBuilder() *connBuilder {
 	return &connBuilder{
 		conn: &connType{
-			aggFields: make(map[string]float64),
-			keys:      config.GenericMap{},
+			aggFields:  make(map[string]float64),
+			keys:       config.GenericMap{},
+			isReported: false,
 		},
 	}
 }

pkg/pipeline/extract/conntrack/conntrack.go

@@ -81,6 +81,8 @@ func (ct *conntrackImpl) Extract(flowLogs []config.GenericMap) []config.GenericM
 				record := conn.toGenericMap()
 				addHashField(record, computedHash.hashTotal)
 				addTypeField(record, api.ConnTrackOutputRecordTypeName("NewConnection"))
+				isFirst := conn.markReported()
+				addIsFirstField(record, isFirst)
 				outputRecords = append(outputRecords, record)
 				ct.metrics.outputRecords.WithLabelValues("newConnection").Inc()
 			}
@@ -123,6 +125,11 @@ func (ct *conntrackImpl) popEndConnections() []config.GenericMap {
 			record := conn.toGenericMap()
 			addHashField(record, conn.getHash().hashTotal)
 			addTypeField(record, api.ConnTrackOutputRecordTypeName("EndConnection"))
+			var isFirst bool
+			if ct.shouldOutputEndConnection {
+				isFirst = conn.markReported()
+			}
+			addIsFirstField(record, isFirst)
 			outputRecords = append(outputRecords, record)
 			shouldDelete, shouldStop = true, false
 		} else {
@@ -144,6 +151,11 @@ func (ct *conntrackImpl) prepareUpdateConnectionRecords() []config.GenericMap {
 			record := conn.toGenericMap()
 			addHashField(record, conn.getHash().hashTotal)
 			addTypeField(record, api.ConnTrackOutputRecordTypeName("UpdateConnection"))
+			var isFirst bool
+			if ct.shouldOutputUpdateConnection {
+				isFirst = conn.markReported()
+			}
+			addIsFirstField(record, isFirst)
 			outputRecords = append(outputRecords, record)
 			newNextUpdate := ct.clock.Now().Add(ct.config.UpdateConnectionInterval.Duration)
 			ct.connStore.updateNextReportTime(conn.getHash().hashTotal, newNextUpdate)
@@ -236,3 +248,7 @@ func addHashField(record config.GenericMap, hashId uint64) {
 func addTypeField(record config.GenericMap, recordType string) {
 	record[api.RecordTypeFieldName] = recordType
 }
+
+func addIsFirstField(record config.GenericMap, isFirst bool) {
+	record[api.IsFirstFieldName] = isFirst
+}