[receiver/otlp, internal, featuregate] Add featuregate to switch to localhost defaults for server-like components

.chloggen/mx-psi_featuregate-localhost-2.yaml

@@ -0,0 +1,26 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: component
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Add `component.UseLocalHostAsDefaultHost` feature gate that changes default endpoints from 0.0.0.0 to localhost"
+
+# One or more tracking issues or pull requests related to the change
+issues: [8510]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: | 
+    The only component in this repository affected by this is the OTLP receiver.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []
+

.chloggen/mx-psi_featuregate-localhost.yaml

@@ -0,0 +1,26 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: featuregate
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Add the `featuregate.ErrAlreadyRegistered` error, which is returned by `featuregate.Registry`'s `Register` when adding a feature gate that is already registered."
+
+# One or more tracking issues or pull requests related to the change
+issues: [8622]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: | 
+  Use `errors.Is` to check for this error.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

featuregate/registry.go

@@ -4,6 +4,7 @@
 package featuregate // import "go.opentelemetry.io/collector/featuregate"
 
 import (
+	"errors"
 	"fmt"
 	"sort"
 	"sync"
@@ -12,6 +13,11 @@ import (
 
 var globalRegistry = NewRegistry()
 
+var (
+	// ErrAlreadyRegistered is returned when adding a Gate that is already registered.
+	ErrAlreadyRegistered = errors.New("gate is already registered")
+)
+
 // GlobalRegistry returns the global Registry.
 func GlobalRegistry() *Registry {
 	return globalRegistry
@@ -100,7 +106,7 @@ func (r *Registry) Register(id string, stage Stage, opts ...RegisterOption) (*Ga
 		return nil, fmt.Errorf("no removal version set for %v gate %q", g.stage.String(), id)
 	}
 	if _, loaded := r.gates.LoadOrStore(id, g); loaded {
-		return nil, fmt.Errorf("attempted to add pre-existing gate %q", id)
+		return nil, fmt.Errorf("failed to register %q: %w", id, ErrAlreadyRegistered)
 	}
 	return g, nil
 }

featuregate/registry_test.go

@@ -33,7 +33,7 @@ func TestRegistry(t *testing.T) {
 	assert.False(t, g.IsEnabled())
 
 	_, err = r.Register(id, StageBeta)
-	assert.Error(t, err)
+	assert.ErrorIs(t, err, ErrAlreadyRegistered)
 	assert.Panics(t, func() {
 		r.MustRegister(id, StageBeta)
 	})

internal/localhostgate/featuregate.go

@@ -0,0 +1,80 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// package localhostgate defines a feature gate that controls whether server-like receivers and extensions use localhost as the default host for their endpoints.
+// This package is duplicated across core and contrib to avoid exposing the feature gate as part of the public API.
+// To do this we define a `registerOrLoad` helper and try to register the gate in both modules.
+// IMPORTANT NOTE: ANY CHANGES TO THIS PACKAGE MUST BE MIRRORED IN THE CONTRIB COUNTERPART.
+package localhostgate // import "go.opentelemetry.io/collector/internal/localhostgate"
+
+import (
+	"errors"
+	"fmt"
+
+	"go.uber.org/zap"
+
+	"go.opentelemetry.io/collector/featuregate"
+)
+
+const useLocalHostAsDefaultHostID = "component.UseLocalHostAsDefaultHost"
+
+// UseLocalHostAsDefaultHostfeatureGate is the feature gate that controls whether
+// server-like receivers and extensions such as the OTLP receiver use localhost as the default host for their endpoints.
+var UseLocalHostAsDefaultHostfeatureGate *featuregate.Gate
+
+// registerOrLoad tries to register the feature gate and loads it if it already exists.
+func registerOrLoad(reg *featuregate.Registry, id string, stage featuregate.Stage, opts ...featuregate.RegisterOption) (*featuregate.Gate, error) {
+	gate, err := reg.Register(id, stage, opts...)
+
+	if err != nil {
+		switch {
+		case errors.Is(err, featuregate.ErrAlreadyRegistered):
+			// Gate is already registered; find it.
+			// Only a handful of feature gates are registered, so it's fine to iterate over all of them.
+			reg.VisitAll(func(g *featuregate.Gate) {
+				if g.ID() == id {
+					gate = g
+					return
+				}
+			})
+		default:
+			// Propagate the error otherwise.
+			return nil, err
+		}
+	}
+
+	return gate, nil
+}
+
+func init() {
+	var err error
+	UseLocalHostAsDefaultHostfeatureGate, err = registerOrLoad(
+		featuregate.GlobalRegistry(),
+		useLocalHostAsDefaultHostID,
+		featuregate.StageAlpha,
+		featuregate.WithRegisterDescription("controls whether server-like receivers and extensions such as the OTLP receiver use localhost as the default host for their endpoints"),
+	)
+
+	if err != nil {
+		panic(err)
+	}
+}
+
+// EndpointForPort gets the endpoint for a given port using localhost or 0.0.0.0 depending on the feature gate.
+func EndpointForPort(port int) string {
+	host := "localhost"
+	if !UseLocalHostAsDefaultHostfeatureGate.IsEnabled() {
+		host = "0.0.0.0"
+	}
+	return fmt.Sprintf("%s:%d", host, port)
+}
+
+// LogAboutUseLocalHostAsDefault logs about the upcoming change from 0.0.0.0 to localhost on server-like components.
+func LogAboutUseLocalHostAsDefault(logger *zap.Logger) {
+	if !UseLocalHostAsDefaultHostfeatureGate.IsEnabled() {
+		logger.Info(
+			"The default endpoint(s) for this component will change in a future version to use localhost instead of 0.0.0.0. Use the feature gate to preview the new default.",
+			zap.String("feature gate ID", useLocalHostAsDefaultHostID),
+		)
+	}
+}

internal/localhostgate/featuregate_test.go

@@ -0,0 +1,57 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package localhostgate
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/collector/featuregate"
+)
+
+func setFeatureGateForTest(t testing.TB, gate *featuregate.Gate, enabled bool) func() {
+	originalValue := gate.IsEnabled()
+	require.NoError(t, featuregate.GlobalRegistry().Set(gate.ID(), enabled))
+	return func() {
+		require.NoError(t, featuregate.GlobalRegistry().Set(gate.ID(), originalValue))
+	}
+}
+
+func TestEndpointForPort(t *testing.T) {
+	tests := []struct {
+		port     int
+		enabled  bool
+		endpoint string
+	}{
+		{
+			port:     4317,
+			enabled:  false,
+			endpoint: "0.0.0.0:4317",
+		},
+		{
+			port:     4317,
+			enabled:  true,
+			endpoint: "localhost:4317",
+		},
+		{
+			port:     0,
+			enabled:  false,
+			endpoint: "0.0.0.0:0",
+		},
+		{
+			port:     0,
+			enabled:  true,
+			endpoint: "localhost:0",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.endpoint, func(t *testing.T) {
+			defer setFeatureGateForTest(t, UseLocalHostAsDefaultHostfeatureGate, tt.enabled)()
+			assert.Equal(t, EndpointForPort(tt.port), tt.endpoint)
+		})
+	}
+}

receiver/otlpreceiver/README.md

@@ -30,7 +30,9 @@ The following settings are configurable:
 
 - `endpoint` (default = 0.0.0.0:4317 for grpc protocol, 0.0.0.0:4318 http protocol):
   host:port to which the receiver is going to receive data. The valid syntax is
-  described at https://github.com/grpc/grpc/blob/master/doc/naming.md.
+  described at https://github.com/grpc/grpc/blob/master/doc/naming.md. The 
+  `component.UseLocalHostAsDefaultHost` feature gate changes these to localhost:4317 and 
+  localhost:4318 respectively. This will become the default in a future release.
 
 ## Advanced Configuration
 

receiver/otlpreceiver/config.go

@@ -44,6 +44,10 @@ type Protocols struct {
 type Config struct {
 	// Protocols is the configuration for the supported protocols, currently gRPC and HTTP (Proto and JSON).
 	Protocols `mapstructure:"protocols"`
+
+	// logLocalHostWarning is used to log a warning if the default unspecified endpoint is used.
+	// Can be removed once component.UseLocalHostAsDefaultHost moves to stable.
+	logLocalHostWarning bool
 }
 
 var _ component.Config = (*Config)(nil)
@@ -67,11 +71,16 @@ func (cfg *Config) Unmarshal(conf *confmap.Conf) error {
 
 	if !conf.IsSet(protoGRPC) {
 		cfg.GRPC = nil
+		cfg.logLocalHostWarning = true // default endpoint used
+	} else {
+		cfg.logLocalHostWarning = cfg.logLocalHostWarning || !conf.IsSet(protoGRPC+confmap.KeyDelimiter+"endpoint")
 	}
 
 	if !conf.IsSet(protoHTTP) {
 		cfg.HTTP = nil
+		cfg.logLocalHostWarning = true // default endpoint used
 	} else {
+		cfg.logLocalHostWarning = cfg.logLocalHostWarning || !conf.IsSet(protoHTTP+confmap.KeyDelimiter+"endpoint")
 		var err error
 
 		if cfg.HTTP.TracesURLPath, err = sanitizeURLPath(cfg.HTTP.TracesURLPath); err != nil {

receiver/otlpreceiver/config_test.go

@@ -20,13 +20,20 @@ import (
 	"go.opentelemetry.io/collector/confmap/confmaptest"
 )
 
+// defaultCfgWithLog creates default config with warning log enabled.
+func defaultCfgWithLog() component.Config {
+	cfg := NewFactory().CreateDefaultConfig()
+	cfg.(*Config).logLocalHostWarning = true
+	return cfg
+}
+
 func TestUnmarshalDefaultConfig(t *testing.T) {
 	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "default.yaml"))
 	require.NoError(t, err)
 	factory := NewFactory()
 	cfg := factory.CreateDefaultConfig()
 	assert.NoError(t, component.UnmarshalConfig(cm, cfg))
-	assert.Equal(t, factory.CreateDefaultConfig(), cfg)
+	assert.Equal(t, defaultCfgWithLog(), cfg)
 }
 
 func TestUnmarshalConfigOnlyGRPC(t *testing.T) {
@@ -36,7 +43,7 @@ func TestUnmarshalConfigOnlyGRPC(t *testing.T) {
 	cfg := factory.CreateDefaultConfig()
 	assert.NoError(t, component.UnmarshalConfig(cm, cfg))
 
-	defaultOnlyGRPC := factory.CreateDefaultConfig().(*Config)
+	defaultOnlyGRPC := defaultCfgWithLog().(*Config)
 	defaultOnlyGRPC.HTTP = nil
 	assert.Equal(t, defaultOnlyGRPC, cfg)
 }
@@ -48,7 +55,7 @@ func TestUnmarshalConfigOnlyHTTP(t *testing.T) {
 	cfg := factory.CreateDefaultConfig()
 	assert.NoError(t, component.UnmarshalConfig(cm, cfg))
 
-	defaultOnlyHTTP := factory.CreateDefaultConfig().(*Config)
+	defaultOnlyHTTP := defaultCfgWithLog().(*Config)
 	defaultOnlyHTTP.GRPC = nil
 	assert.Equal(t, defaultOnlyHTTP, cfg)
 }
@@ -60,7 +67,7 @@ func TestUnmarshalConfigOnlyHTTPNull(t *testing.T) {
 	cfg := factory.CreateDefaultConfig()
 	assert.NoError(t, component.UnmarshalConfig(cm, cfg))
 
-	defaultOnlyHTTP := factory.CreateDefaultConfig().(*Config)
+	defaultOnlyHTTP := defaultCfgWithLog().(*Config)
 	defaultOnlyHTTP.GRPC = nil
 	assert.Equal(t, defaultOnlyHTTP, cfg)
 }
@@ -72,7 +79,7 @@ func TestUnmarshalConfigOnlyHTTPEmptyMap(t *testing.T) {
 	cfg := factory.CreateDefaultConfig()
 	assert.NoError(t, component.UnmarshalConfig(cm, cfg))
 
-	defaultOnlyHTTP := factory.CreateDefaultConfig().(*Config)
+	defaultOnlyHTTP := defaultCfgWithLog().(*Config)
 	defaultOnlyHTTP.GRPC = nil
 	assert.Equal(t, defaultOnlyHTTP, cfg)
 }
@@ -134,6 +141,7 @@ func TestUnmarshalConfig(t *testing.T) {
 					LogsURLPath:    "/log/ingest",
 				},
 			},
+			logLocalHostWarning: true,
 		}, cfg)
 
 }

receiver/otlpreceiver/factory.go

@@ -11,15 +11,16 @@ import (
 	"go.opentelemetry.io/collector/config/confighttp"
 	"go.opentelemetry.io/collector/config/confignet"
 	"go.opentelemetry.io/collector/consumer"
+	"go.opentelemetry.io/collector/internal/localhostgate"
 	"go.opentelemetry.io/collector/internal/sharedcomponent"
 	"go.opentelemetry.io/collector/receiver"
 )
 
 const (
 	typeStr = "otlp"
 
-	defaultGRPCEndpoint = "0.0.0.0:4317"
-	defaultHTTPEndpoint = "0.0.0.0:4318"
+	grpcPort = 4317
+	httpPort = 4318
 
 	defaultTracesURLPath  = "/v1/traces"
 	defaultMetricsURLPath = "/v1/metrics"
@@ -42,15 +43,15 @@ func createDefaultConfig() component.Config {
 		Protocols: Protocols{
 			GRPC: &configgrpc.GRPCServerSettings{
 				NetAddr: confignet.NetAddr{
-					Endpoint:  defaultGRPCEndpoint,
+					Endpoint:  localhostgate.EndpointForPort(grpcPort),
 					Transport: "tcp",
 				},
 				// We almost write 0 bytes, so no need to tune WriteBufferSize.
 				ReadBufferSize: 512 * 1024,
 			},
 			HTTP: &HTTPConfig{
 				HTTPServerSettings: &confighttp.HTTPServerSettings{
-					Endpoint: defaultHTTPEndpoint,
+					Endpoint: localhostgate.EndpointForPort(httpPort),
 				},
 				TracesURLPath:  defaultTracesURLPath,
 				MetricsURLPath: defaultMetricsURLPath,