sdk/resource: honor OTEL_SERVICE_NAME in fromEnv resource detector

CHANGELOG.md

@@ -33,6 +33,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   This method returns the number of list-members the `TraceState` holds. (#1937)
 - Creates package `go.opentelemetry.io/otel/exporters/otlp/otlptrace` that defines a trace exporter that uses a `otlptrace.Client` to send data.
   Creates package `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc` implementing a gRPC `otlptrace.Client` and offers convenience functions, `NewExportPipeline` and `InstallNewPipeline`, to setup and install a `otlptrace.Exporter` in tracing .(#1922)
+- The `OTEL_SERVICE_NAME` environment variable is the preferred source for `service.name`, used by the environment resource detector if a service name is present both there and in `OTEL_RESOURCE_ATTRIBUTES`. (#1969)
 
 ### Changed
 

sdk/resource/env.go

@@ -21,10 +21,16 @@ import (
 	"strings"
 
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/semconv"
 )
 
-// envVar is the environment variable name OpenTelemetry Resource information can be assigned to.
-const envVar = "OTEL_RESOURCE_ATTRIBUTES"
+const (
+	// resourceAttrKey is the environment variable name OpenTelemetry Resource information will be read from.
+	resourceAttrKey = "OTEL_RESOURCE_ATTRIBUTES"
+
+	// svcNameKey is the environment variable name that Service Name information will be read from.
+	svcNameKey = "OTEL_SERVICE_NAME"
+)
 
 var (
 	// errMissingValue is returned when a resource value is missing.
@@ -33,22 +39,32 @@ var (
 
 // fromEnv is a Detector that implements the Detector and collects
 // resources from environment.  This Detector is included as a
-// builtin.  If these resource attributes are not wanted, use the
-// WithFromEnv(nil) or WithoutBuiltin() options to explicitly disable
-// them.
+// builtin.
 type fromEnv struct{}
 
 // compile time assertion that FromEnv implements Detector interface
 var _ Detector = fromEnv{}
 
 // Detect collects resources from environment
 func (fromEnv) Detect(context.Context) (*Resource, error) {
-	attrs := strings.TrimSpace(os.Getenv(envVar))
+	attrs := strings.TrimSpace(os.Getenv(resourceAttrKey))
+	svcName := strings.TrimSpace(os.Getenv(svcNameKey))
 
-	if attrs == "" {
+	if attrs == "" && svcName == "" {
 		return Empty(), nil
 	}
-	return constructOTResources(attrs)
+
+	var res *Resource
+
+	if svcName != "" {
+		res = NewWithAttributes(semconv.ServiceNameKey.String(svcName))
+	}
+
+	r2, err := constructOTResources(attrs)
+
+	// Ensure that the resource with the service name from OTEL_SERVICE_NAME
+	// takes precedence, if it was defined.
+	return Merge(r2, res), err
 }
 
 func constructOTResources(s string) (*Resource, error) {

sdk/resource/env_test.go

@@ -24,11 +24,12 @@ import (
 
 	"go.opentelemetry.io/otel/attribute"
 	ottest "go.opentelemetry.io/otel/internal/internaltest"
+	"go.opentelemetry.io/otel/semconv"
 )
 
 func TestDetectOnePair(t *testing.T) {
 	store, err := ottest.SetEnvVariables(map[string]string{
-		envVar: "key=value",
+		resourceAttrKey: "key=value",
 	})
 	require.NoError(t, err)
 	defer func() { require.NoError(t, store.Restore()) }()
@@ -41,8 +42,8 @@ func TestDetectOnePair(t *testing.T) {
 
 func TestDetectMultiPairs(t *testing.T) {
 	store, err := ottest.SetEnvVariables(map[string]string{
-		"x":    "1",
-		envVar: "key=value, k = v , a= x, a=z",
+		"x":             "1",
+		resourceAttrKey: "key=value, k = v , a= x, a=z",
 	})
 	require.NoError(t, err)
 	defer func() { require.NoError(t, store.Restore()) }()
@@ -60,7 +61,7 @@ func TestDetectMultiPairs(t *testing.T) {
 
 func TestEmpty(t *testing.T) {
 	store, err := ottest.SetEnvVariables(map[string]string{
-		envVar: "   ",
+		resourceAttrKey: "   ",
 	})
 	require.NoError(t, err)
 	defer func() { require.NoError(t, store.Restore()) }()
@@ -73,7 +74,7 @@ func TestEmpty(t *testing.T) {
 
 func TestMissingKeyError(t *testing.T) {
 	store, err := ottest.SetEnvVariables(map[string]string{
-		envVar: "key=value,key",
+		resourceAttrKey: "key=value,key",
 	})
 	require.NoError(t, err)
 	defer func() { require.NoError(t, store.Restore()) }()
@@ -86,3 +87,20 @@ func TestMissingKeyError(t *testing.T) {
 		attribute.String("key", "value"),
 	))
 }
+
+func TestDetectServiceNameFromEnv(t *testing.T) {
+	store, err := ottest.SetEnvVariables(map[string]string{
+		resourceAttrKey: "key=value,service.name=foo",
+		svcNameKey:      "bar",
+	})
+	require.NoError(t, err)
+	defer func() { require.NoError(t, store.Restore()) }()
+
+	detector := &fromEnv{}
+	res, err := detector.Detect(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, res, NewWithAttributes(
+		attribute.String("key", "value"),
+		semconv.ServiceNameKey.String("bar"),
+	))
+}