otelcol: remove default telemetry factory (#14062)

#### Description

Remove the default telemetry factory, and require callers to specify
one, to keep things maintainable.

#### Link to tracking issue

Fixes #14003

#### Testing

<!--Describe the documentation added.-->
#### Documentation

N/A

Author: axw

.chloggen/otelcol-factoriestelemetry-required.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: pkg/otelcol
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: The `otelcol.Factories.Telemetry` field is now required
+
+# One or more tracking issues or pull requests related to the change
+issues: [14003]
+
+# (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: |
+  Previously if this field was not set, then it would default to an otelconftelemetry factory.
+  Callers of the otelcol package must now set the field explicitly.
+
+# 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]

otelcol/collector.go

@@ -25,7 +25,6 @@ import (
 	"go.opentelemetry.io/collector/confmap/xconfmap"
 	"go.opentelemetry.io/collector/otelcol/internal/grpclog"
 	"go.opentelemetry.io/collector/service"
-	"go.opentelemetry.io/collector/service/telemetry/otelconftelemetry"
 )
 
 // State defines Collector's state.
@@ -179,9 +178,6 @@ func (col *Collector) setupConfigurationComponents(ctx context.Context) error {
 	if err != nil {
 		return fmt.Errorf("failed to initialize factories: %w", err)
 	}
-	if factories.Telemetry == nil {
-		factories.Telemetry = otelconftelemetry.NewFactory()
-	}
 
 	cfg, err := col.configProvider.Get(ctx, factories)
 	if err != nil {
@@ -274,9 +270,6 @@ func (col *Collector) DryRun(ctx context.Context) error {
 	if err != nil {
 		return fmt.Errorf("failed to initialize factories: %w", err)
 	}
-	if factories.Telemetry == nil {
-		factories.Telemetry = otelconftelemetry.NewFactory()
-	}
 
 	cfg, err := col.configProvider.Get(ctx, factories)
 	if err != nil {

otelcol/collector_test.go

@@ -397,17 +397,6 @@ func TestCollectorRun(t *testing.T) {
 			factories:  nopFactories,
 			configFile: "otelcol-nop.yaml",
 		},
-		"defaul_telemetry_factory": {
-			factories: func() (Factories, error) {
-				factories, err := nopFactories()
-				if err != nil {
-					return Factories{}, err
-				}
-				factories.Telemetry = nil
-				return factories, nil
-			},
-			configFile: "otelcol-otelconftelemetry.yaml",
-		},
 	}
 
 	for name, test := range tests {
@@ -477,6 +466,18 @@ func TestCollectorRun_Errors(t *testing.T) {
 			},
 			expectedErr: "failed to get config: cannot unmarshal the configuration: decoding failed due to the following error(s):\n\n'service.telemetry' has invalid keys: unknown",
 		},
+		"missing_telemetry_factory": {
+			settings: CollectorSettings{
+				BuildInfo: component.NewDefaultBuildInfo(),
+				Factories: func() (Factories, error) {
+					factories, _ := nopFactories()
+					factories.Telemetry = nil
+					return factories, nil
+				},
+				ConfigProviderSettings: newDefaultConfigProviderSettings(t, []string{filepath.Join("testdata", "otelcol-otelconftelemetry.yaml")}),
+			},
+			expectedErr: "failed to get config: cannot unmarshal the configuration: otelcol.Factories.Telemetry must not be nil. For example, you can use otelconftelemetry.NewFactory to build a telemetry factory",
+		},
 	}
 
 	for name, test := range tests {
@@ -548,19 +549,17 @@ func TestCollectorDryRun(t *testing.T) {
 			},
 			expectedErr: "failed to get config: cannot unmarshal the configuration: decoding failed due to the following error(s):\n\n'service.telemetry' has invalid keys: unknown",
 		},
-		"default_telemetry_factory": {
+		"missing_telemetry_factory": {
 			settings: CollectorSettings{
 				BuildInfo: component.NewDefaultBuildInfo(),
 				Factories: func() (Factories, error) {
-					factories, err := nopFactories()
-					if err != nil {
-						return Factories{}, err
-					}
+					factories, _ := nopFactories()
 					factories.Telemetry = nil
 					return factories, nil
 				},
 				ConfigProviderSettings: newDefaultConfigProviderSettings(t, []string{filepath.Join("testdata", "otelcol-otelconftelemetry.yaml")}),
 			},
+			expectedErr: "failed to get config: cannot unmarshal the configuration: otelcol.Factories.Telemetry must not be nil. For example, you can use otelconftelemetry.NewFactory to build a telemetry factory",
 		},
 	}
 

otelcol/factories.go

@@ -34,10 +34,6 @@ type Factories struct {
 	Connectors map[component.Type]connector.Factory
 
 	// Telemetry is the factory to create the telemetry providers for the service.
-	//
-	// If Telemetry is nil, otelconftelemetry will be used by default.
-	// TODO remove the backwards compatibility and require a non-nil factory
-	// https://github.com/open-telemetry/opentelemetry-collector/issues/14003
 	Telemetry telemetry.Factory
 
 	// ReceiverModules maps receiver types to their respective go modules.

otelcol/otelcoltest/config.go

@@ -13,17 +13,15 @@ import (
 	"go.opentelemetry.io/collector/confmap/provider/yamlprovider"
 	"go.opentelemetry.io/collector/confmap/xconfmap"
 	"go.opentelemetry.io/collector/otelcol"
-	"go.opentelemetry.io/collector/service/telemetry/otelconftelemetry"
 )
 
-// LoadConfig loads a config.Config  from file, and does NOT validate the configuration.
+// LoadConfig loads a config.Config from file, and does NOT validate the configuration.
 //
-// If factories.Telemetry is nil, otelconftelemetry will be used by default.
-// TODO remove the backwards compatibility and require a non-nil factory
-// https://github.com/open-telemetry/opentelemetry-collector/issues/14003
+// If factories.Telemetry is nil, a no-op telemetry factory will be used. This
+// factory does not support any telemetry configuration.
 func LoadConfig(fileName string, factories otelcol.Factories) (*otelcol.Config, error) {
 	if factories.Telemetry == nil {
-		factories.Telemetry = otelconftelemetry.NewFactory()
+		factories.Telemetry = nopTelemetryFactory()
 	}
 	provider, err := otelcol.NewConfigProvider(otelcol.ConfigProviderSettings{
 		ResolverSettings: confmap.ResolverSettings{

otelcol/otelcoltest/config_test.go

@@ -13,7 +13,6 @@ import (
 	"go.opentelemetry.io/collector/component"
 	"go.opentelemetry.io/collector/pipeline"
 	"go.opentelemetry.io/collector/service/pipelines"
-	"go.opentelemetry.io/collector/service/telemetry/otelconftelemetry"
 )
 
 func TestLoadConfig(t *testing.T) {
@@ -64,15 +63,15 @@ func TestLoadConfig(t *testing.T) {
 	assert.Equal(t, struct{}{}, cfg.Service.Telemetry)
 }
 
-func TestLoadConfig_DefaultTelemetry(t *testing.T) {
+func TestLoadConfig_DefaultNopTelemetry(t *testing.T) {
 	factories, err := NopFactories()
 	require.NoError(t, err)
 	factories.Telemetry = nil
 
 	cfg, err := LoadConfig(filepath.Join("testdata", "config.yaml"), factories)
 	require.NoError(t, err)
 
-	assert.Equal(t, otelconftelemetry.NewFactory().CreateDefaultConfig(), cfg.Service.Telemetry)
+	assert.Equal(t, struct{}{}, cfg.Service.Telemetry)
 }
 
 func TestLoadConfigAndValidate(t *testing.T) {

otelcol/otelcoltest/nop_factories.go

@@ -24,9 +24,13 @@ func NopFactories() (otelcol.Factories, error) {
 	factories.Exporters, _ = otelcol.MakeFactoryMap(exportertest.NewNopFactory())
 	factories.Processors, _ = otelcol.MakeFactoryMap(processortest.NewNopFactory())
 	factories.Connectors, _ = otelcol.MakeFactoryMap(connectortest.NewNopFactory())
-	factories.Telemetry = telemetry.NewFactory(
-		func() component.Config { return struct{}{} },
-	)
+	factories.Telemetry = nopTelemetryFactory()
 
 	return factories, nil
 }
+
+func nopTelemetryFactory() telemetry.Factory {
+	return telemetry.NewFactory(
+		func() component.Config { return struct{}{} },
+	)
+}

otelcol/unmarshaler.go

@@ -4,6 +4,8 @@
 package otelcol // import "go.opentelemetry.io/collector/otelcol"
 
 import (
+	"errors"
+
 	"go.opentelemetry.io/collector/confmap"
 	"go.opentelemetry.io/collector/connector"
 	"go.opentelemetry.io/collector/exporter"
@@ -14,6 +16,8 @@ import (
 	"go.opentelemetry.io/collector/service"
 )
 
+var errNilTelemetryFactory = errors.New("otelcol.Factories.Telemetry must not be nil. For example, you can use otelconftelemetry.NewFactory to build a telemetry factory")
+
 type configSettings struct {
 	Receivers  *configunmarshaler.Configs[receiver.Factory]  `mapstructure:"receivers"`
 	Processors *configunmarshaler.Configs[processor.Factory] `mapstructure:"processors"`
@@ -26,6 +30,10 @@ type configSettings struct {
 // unmarshal the configSettings from a confmap.Conf.
 // After the config is unmarshalled, `Validate()` must be called to validate.
 func unmarshal(v *confmap.Conf, factories Factories) (*configSettings, error) {
+	if factories.Telemetry == nil {
+		return nil, errNilTelemetryFactory
+	}
+
 	// Unmarshal top level sections and validate.
 	cfg := &configSettings{
 		Receivers:  configunmarshaler.NewConfigs(factories.Receivers),