[system detector] Fallback to os.Hostname when FQDN is not available (open-telemetry#3099)

- Fall back to `os.Hostname` when FQDN is not available.

**Link to tracking Issue:** Fixes open-telemetry#3092

Author: mx-psi

processor/resourcedetectionprocessor/internal/system/metadata.go

@@ -15,13 +15,17 @@
 package system
 
 import (
+	"os"
 	"runtime"
 	"strings"
 
 	"github.com/Showmax/go-fqdn"
 )
 
 type systemMetadata interface {
+	// Hostname returns the OS hostname
+	Hostname() (string, error)
+
 	// FQDN returns the fully qualified domain name
 	FQDN() (string, error)
 
@@ -47,3 +51,7 @@ func (*systemMetadataImpl) OSType() (string, error) {
 func (*systemMetadataImpl) FQDN() (string, error) {
 	return fqdn.FqdnHostname()
 }
+
+func (*systemMetadataImpl) Hostname() (string, error) {
+	return os.Hostname()
+}

processor/resourcedetectionprocessor/internal/system/system.go

@@ -21,6 +21,7 @@ import (
 	"go.opentelemetry.io/collector/component"
 	"go.opentelemetry.io/collector/consumer/pdata"
 	"go.opentelemetry.io/collector/translator/conventions"
+	"go.uber.org/zap"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/processor/resourcedetectionprocessor/internal"
 )
@@ -35,11 +36,12 @@ var _ internal.Detector = (*Detector)(nil)
 // Detector is a system metadata detector
 type Detector struct {
 	provider systemMetadata
+	logger   *zap.Logger
 }
 
 // NewDetector creates a new system metadata detector
-func NewDetector(component.ProcessorCreateParams, internal.DetectorConfig) (internal.Detector, error) {
-	return &Detector{provider: &systemMetadataImpl{}}, nil
+func NewDetector(p component.ProcessorCreateParams, _ internal.DetectorConfig) (internal.Detector, error) {
+	return &Detector{provider: &systemMetadataImpl{}, logger: p.Logger}, nil
 }
 
 // Detect detects system metadata and returns a resource with the available ones
@@ -52,12 +54,17 @@ func (d *Detector) Detect(_ context.Context) (pdata.Resource, error) {
 		return res, fmt.Errorf("failed getting OS type: %w", err)
 	}
 
-	fqdn, err := d.provider.FQDN()
+	hostname, err := d.provider.FQDN()
 	if err != nil {
-		return res, fmt.Errorf("failed getting FQDN: %w", err)
+		// Fallback to OS hostname
+		d.logger.Debug("FQDN query failed, falling back to OS hostname", zap.Error(err))
+		hostname, err = d.provider.Hostname()
+		if err != nil {
+			return res, fmt.Errorf("failed getting OS hostname: %w", err)
+		}
 	}
 
-	attrs.InsertString(conventions.AttributeHostName, fqdn)
+	attrs.InsertString(conventions.AttributeHostName, hostname)
 	attrs.InsertString(conventions.AttributeOSType, osType)
 
 	return res, nil

processor/resourcedetectionprocessor/internal/system/system_test.go

@@ -33,6 +33,11 @@ type mockMetadata struct {
 	mock.Mock
 }
 
+func (m *mockMetadata) Hostname() (string, error) {
+	args := m.MethodCalled("Hostname")
+	return args.String(0), args.Error(1)
+}
+
 func (m *mockMetadata) FQDN() (string, error) {
 	args := m.MethodCalled("FQDN")
 	return args.String(0), args.Error(1)
@@ -54,7 +59,7 @@ func TestDetectFQDNAvailable(t *testing.T) {
 	md.On("FQDN").Return("fqdn", nil)
 	md.On("OSType").Return("DARWIN", nil)
 
-	detector := &Detector{provider: md}
+	detector := &Detector{provider: md, logger: zap.NewNop()}
 	res, err := detector.Detect(context.Background())
 	require.NoError(t, err)
 	md.AssertExpectations(t)
@@ -70,23 +75,45 @@ func TestDetectFQDNAvailable(t *testing.T) {
 
 }
 
+func TestFallbackHostname(t *testing.T) {
+	mdHostname := &mockMetadata{}
+	mdHostname.On("Hostname").Return("hostname", nil)
+	mdHostname.On("FQDN").Return("", errors.New("err"))
+	mdHostname.On("OSType").Return("DARWIN", nil)
+
+	detector := &Detector{provider: mdHostname, logger: zap.NewNop()}
+	res, err := detector.Detect(context.Background())
+	require.NoError(t, err)
+	mdHostname.AssertExpectations(t)
+	res.Attributes().Sort()
+
+	expected := internal.NewResource(map[string]interface{}{
+		conventions.AttributeHostName: "hostname",
+		conventions.AttributeOSType:   "DARWIN",
+	})
+	expected.Attributes().Sort()
+
+	assert.Equal(t, expected, res)
+}
+
 func TestDetectError(t *testing.T) {
-	// FQDN fails
+	// FQDN and hostname fail
 	mdFQDN := &mockMetadata{}
 	mdFQDN.On("OSType").Return("WINDOWS", nil)
 	mdFQDN.On("FQDN").Return("", errors.New("err"))
+	mdFQDN.On("Hostname").Return("", errors.New("err"))
 
-	detector := &Detector{provider: mdFQDN}
+	detector := &Detector{provider: mdFQDN, logger: zap.NewNop()}
 	res, err := detector.Detect(context.Background())
 	assert.Error(t, err)
 	assert.True(t, internal.IsEmptyResource(res))
 
-	// Hostname fails
-	mdHostname := &mockMetadata{}
-	mdHostname.On("FQDN").Return("fqdn", nil)
-	mdHostname.On("OSType").Return("", errors.New("err"))
+	// OS type fails
+	mdOSType := &mockMetadata{}
+	mdOSType.On("FQDN").Return("fqdn", nil)
+	mdOSType.On("OSType").Return("", errors.New("err"))
 
-	detector = &Detector{provider: mdHostname}
+	detector = &Detector{provider: mdOSType, logger: zap.NewNop()}
 	res, err = detector.Detect(context.Background())
 	assert.Error(t, err)
 	assert.True(t, internal.IsEmptyResource(res))