metricbeat: handle nf_conntrack module not loaded in linux integration (

#41930)

* metricbeat: handle nf_conntrack module not loaded in linux integration

* ci lint fixes

* fix error check to prevent windows failure

metricbeat/module/linux/conntrack/conntrack.go

@@ -19,6 +19,7 @@ package conntrack
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/prometheus/procfs"
 
@@ -50,7 +51,10 @@ type MetricSet struct {
 func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 	cfgwarn.Beta("The linux conntrack metricset is beta.")
 
-	sys := base.Module().(resolve.Resolver)
+	sys, ok := base.Module().(resolve.Resolver)
+	if !ok {
+		return nil, fmt.Errorf("unexpected module type: %T", base.Module())
+	}
 
 	return &MetricSet{
 		BaseMetricSet: base,
@@ -68,6 +72,9 @@ func (m *MetricSet) Fetch(report mb.ReporterV2) error {
 	}
 	conntrackStats, err := newFS.ConntrackStat()
 	if err != nil {
+		if os.IsNotExist(err) {
+			err = mb.PartialMetricsError{Err: fmt.Errorf("nf_conntrack kernel module not loaded: %w", err)}
+		}
 		return fmt.Errorf("error fetching conntrack stats: %w", err)
 	}
 

metricbeat/module/linux/conntrack/conntrack_test.go

@@ -18,10 +18,15 @@
 package conntrack
 
 import (
+	"errors"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
+	"github.com/elastic/beats/v7/metricbeat/mb"
 	mbtest "github.com/elastic/beats/v7/metricbeat/mb/testing"
 	_ "github.com/elastic/beats/v7/metricbeat/module/linux"
 	"github.com/elastic/elastic-agent-libs/mapstr"
@@ -60,6 +65,23 @@ func TestFetch(t *testing.T) {
 	assert.Equal(t, testConn, rawEvent)
 }
 
+func TestFetchConntrackModuleNotLoaded(t *testing.T) {
+	// Create a temporary directory to simulate a missing /proc/net/stat/nf_conntrack file
+	tmpDir := t.TempDir()
+	assert.NoError(t, os.MkdirAll(filepath.Join(tmpDir, "proc/net/stat"), 0755))
+	c := getConfig()
+	c["hostfs"] = tmpDir
+
+	f := mbtest.NewReportingMetricSetV2Error(t, c)
+	events, errs := mbtest.ReportingFetchV2Error(f)
+
+	require.Len(t, errs, 1)
+	err := errors.Join(errs...)
+	assert.ErrorAs(t, err, &mb.PartialMetricsError{})
+	assert.Contains(t, err.Error(), "error fetching conntrack stats: nf_conntrack kernel module not loaded")
+	require.Empty(t, events)
+}
+
 func getConfig() map[string]interface{} {
 	return map[string]interface{}{
 		"module":     "linux",