[service/telemetry] Switch to a factory pattern (open-telemetry#10001)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

Switches `service/telemetry` to a factory pattern. To avoid adding a lot
of public API in one go:
1. the actual factory builder is in an internal package
2. I have not added the `CreateMeterProvider` method yet

There are two goals with this: one is to make progress on open-telemetry#4970, the
other is to allow initializing telemetry sooner:

<!-- Issue number if applicable -->
#### Link to tracking issue
Updates open-telemetry#4970. 

<!--Describe what testing was performed and which tests were added.-->
#### Testing

Updates existing tests to use `NewFactory`

.chloggen/mx-psi_tel-factory.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: deprecation
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: service/telemetry
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Deprecate telemetry.New in favor of telemetry.NewFactory
+
+# One or more tracking issues or pull requests related to the change
+issues: [4970]
+
+# (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:
+
+# 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/unmarshaler.go

@@ -4,11 +4,6 @@
 package otelcol // import "go.opentelemetry.io/collector/otelcol"
 
 import (
-	"time"
-
-	"go.uber.org/zap/zapcore"
-
-	"go.opentelemetry.io/collector/config/configtelemetry"
 	"go.opentelemetry.io/collector/confmap"
 	"go.opentelemetry.io/collector/connector"
 	"go.opentelemetry.io/collector/exporter"
@@ -32,6 +27,10 @@ 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) {
+
+	telFactory := telemetry.NewFactory()
+	defaultTelConfig := *telFactory.CreateDefaultConfig().(*telemetry.Config)
+
 	// Unmarshal top level sections and validate.
 	cfg := &configSettings{
 		Receivers:  configunmarshaler.NewConfigs(factories.Receivers),
@@ -41,28 +40,7 @@ func unmarshal(v *confmap.Conf, factories Factories) (*configSettings, error) {
 		Extensions: configunmarshaler.NewConfigs(factories.Extensions),
 		// TODO: Add a component.ServiceFactory to allow this to be defined by the Service.
 		Service: service.Config{
-			Telemetry: telemetry.Config{
-				Logs: telemetry.LogsConfig{
-					Level:       zapcore.InfoLevel,
-					Development: false,
-					Encoding:    "console",
-					Sampling: &telemetry.LogsSamplingConfig{
-						Enabled:    true,
-						Tick:       10 * time.Second,
-						Initial:    10,
-						Thereafter: 100,
-					},
-					OutputPaths:       []string{"stderr"},
-					ErrorOutputPaths:  []string{"stderr"},
-					DisableCaller:     false,
-					DisableStacktrace: false,
-					InitialFields:     map[string]any(nil),
-				},
-				Metrics: telemetry.MetricsConfig{
-					Level:   configtelemetry.LevelNormal,
-					Address: ":8888",
-				},
-			},
+			Telemetry: defaultTelConfig,
 		},
 	}
 

service/service.go

@@ -89,16 +89,27 @@ func New(ctx context.Context, set Settings, cfg Config) (*Service, error) {
 		},
 		collectorConf: set.CollectorConf,
 	}
-	tel, err := telemetry.New(ctx, telemetry.Settings{BuildInfo: set.BuildInfo, ZapOptions: set.LoggingOptions}, cfg.Telemetry)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get logger: %w", err)
-	}
 
 	// Fetch data for internal telemetry like instance id and sdk version to provide for internal telemetry.
 	res := resource.New(set.BuildInfo, cfg.Telemetry.Resource)
 	pcommonRes := pdataFromSdk(res)
 
-	logger := tel.Logger()
+	telFactory := telemetry.NewFactory()
+	telset := telemetry.Settings{
+		BuildInfo:  set.BuildInfo,
+		ZapOptions: set.LoggingOptions,
+	}
+
+	logger, err := telFactory.CreateLogger(ctx, telset, &cfg.Telemetry)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create logger: %w", err)
+	}
+
+	tracerProvider, err := telFactory.CreateTracerProvider(ctx, telset, &cfg.Telemetry)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create tracer provider: %w", err)
+	}
+
 	logger.Info("Setting up own telemetry...")
 	mp, err := newMeterProvider(
 		meterProviderSettings{
@@ -116,7 +127,7 @@ func New(ctx context.Context, set Settings, cfg Config) (*Service, error) {
 	srv.telemetrySettings = servicetelemetry.TelemetrySettings{
 		Logger:         logger,
 		MeterProvider:  mp,
-		TracerProvider: tel.TracerProvider(),
+		TracerProvider: tracerProvider,
 		MetricsLevel:   cfg.Telemetry.Metrics.Level,
 		// Construct telemetry attributes from build info and config's resource attributes.
 		Resource: pcommonRes,

service/telemetry/factory.go

@@ -0,0 +1,59 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package telemetry // import "go.opentelemetry.io/collector/service/telemetry"
+
+import (
+	"context"
+	"time"
+
+	"go.opentelemetry.io/otel/trace"
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/config/configtelemetry"
+	"go.opentelemetry.io/collector/service/telemetry/internal"
+)
+
+func createDefaultConfig() component.Config {
+	return &Config{
+		Logs: LogsConfig{
+			Level:       zapcore.InfoLevel,
+			Development: false,
+			Encoding:    "console",
+			Sampling: &LogsSamplingConfig{
+				Enabled:    true,
+				Tick:       10 * time.Second,
+				Initial:    10,
+				Thereafter: 100,
+			},
+			OutputPaths:       []string{"stderr"},
+			ErrorOutputPaths:  []string{"stderr"},
+			DisableCaller:     false,
+			DisableStacktrace: false,
+			InitialFields:     map[string]any(nil),
+		},
+		Metrics: MetricsConfig{
+			Level:   configtelemetry.LevelNormal,
+			Address: ":8888",
+		},
+	}
+}
+
+// Factory is a telemetry factory.
+type Factory = internal.Factory
+
+// NewFactory creates a new Factory.
+func NewFactory() Factory {
+	return internal.NewFactory(createDefaultConfig,
+		internal.WithLogger(func(_ context.Context, set Settings, cfg component.Config) (*zap.Logger, error) {
+			c := *cfg.(*Config)
+			return newLogger(c.Logs, set.ZapOptions)
+		}),
+		internal.WithTracerProvider(func(ctx context.Context, _ Settings, cfg component.Config) (trace.TracerProvider, error) {
+			c := *cfg.(*Config)
+			return newTracerProvider(ctx, c)
+		}),
+	)
+}

service/telemetry/internal/factory.go

@@ -0,0 +1,116 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package internal // import "go.opentelemetry.io/collector/service/telemetry/internal"
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/trace"
+	tracenoop "go.opentelemetry.io/otel/trace/noop"
+	"go.uber.org/zap"
+
+	"go.opentelemetry.io/collector/component"
+)
+
+// CreateSettings holds configuration for building Telemetry.
+type CreateSettings struct {
+	BuildInfo         component.BuildInfo
+	AsyncErrorChannel chan error
+	ZapOptions        []zap.Option
+}
+
+// Factory is factory interface for telemetry.
+// This interface cannot be directly implemented. Implementations must
+// use the NewFactory to implement it.
+type Factory interface {
+	// CreateDefaultConfig creates the default configuration for the telemetry.
+	// TODO: Should we just inherit from component.Factory?
+	CreateDefaultConfig() component.Config
+
+	// CreateLogger creates a logger.
+	CreateLogger(ctx context.Context, set CreateSettings, cfg component.Config) (*zap.Logger, error)
+
+	// CreateTracerProvider creates a TracerProvider.
+	CreateTracerProvider(ctx context.Context, set CreateSettings, cfg component.Config) (trace.TracerProvider, error)
+
+	// TODO: Add CreateMeterProvider.
+
+	// unexportedFactoryFunc is used to prevent external implementations of Factory.
+	unexportedFactoryFunc()
+}
+
+// FactoryOption apply changes to Factory.
+type FactoryOption interface {
+	// applyTelemetryFactoryOption applies the option.
+	applyTelemetryFactoryOption(o *factory)
+}
+
+var _ FactoryOption = (*factoryOptionFunc)(nil)
+
+// factoryOptionFunc is an FactoryOption created through a function.
+type factoryOptionFunc func(*factory)
+
+func (f factoryOptionFunc) applyTelemetryFactoryOption(o *factory) {
+	f(o)
+}
+
+var _ Factory = (*factory)(nil)
+
+// factory is the implementation of Factory.
+type factory struct {
+	createDefaultConfig component.CreateDefaultConfigFunc
+	CreateLoggerFunc
+	CreateTracerProviderFunc
+}
+
+func (f *factory) CreateDefaultConfig() component.Config {
+	return f.createDefaultConfig()
+}
+
+// CreateLoggerFunc is the equivalent of Factory.CreateLogger.
+type CreateLoggerFunc func(context.Context, CreateSettings, component.Config) (*zap.Logger, error)
+
+// WithLogger overrides the default no-op logger.
+func WithLogger(createLogger CreateLoggerFunc) FactoryOption {
+	return factoryOptionFunc(func(o *factory) {
+		o.CreateLoggerFunc = createLogger
+	})
+}
+
+func (f *factory) CreateLogger(ctx context.Context, set CreateSettings, cfg component.Config) (*zap.Logger, error) {
+	if f.CreateLoggerFunc == nil {
+		return zap.NewNop(), nil
+	}
+	return f.CreateLoggerFunc(ctx, set, cfg)
+}
+
+// CreateTracerProviderFunc is the equivalent of Factory.CreateTracerProvider.
+type CreateTracerProviderFunc func(context.Context, CreateSettings, component.Config) (trace.TracerProvider, error)
+
+// WithTracerProvider overrides the default no-op tracer provider.
+func WithTracerProvider(createTracerProvider CreateTracerProviderFunc) FactoryOption {
+	return factoryOptionFunc(func(o *factory) {
+		o.CreateTracerProviderFunc = createTracerProvider
+	})
+}
+
+func (f *factory) CreateTracerProvider(ctx context.Context, set CreateSettings, cfg component.Config) (trace.TracerProvider, error) {
+	if f.CreateTracerProviderFunc == nil {
+		return tracenoop.NewTracerProvider(), nil
+	}
+	return f.CreateTracerProviderFunc(ctx, set, cfg)
+}
+
+func (f *factory) unexportedFactoryFunc() {}
+
+// NewFactory returns a new Factory.
+func NewFactory(createDefaultConfig component.CreateDefaultConfigFunc, options ...FactoryOption) Factory {
+	f := &factory{
+		createDefaultConfig: createDefaultConfig,
+	}
+	for _, op := range options {
+		op.applyTelemetryFactoryOption(f)
+	}
+	return f
+}

service/telemetry/logger.go

@@ -0,0 +1,53 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package telemetry // import "go.opentelemetry.io/collector/service/telemetry"
+
+import (
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+func newLogger(cfg LogsConfig, options []zap.Option) (*zap.Logger, error) {
+	// Copied from NewProductionConfig.
+	zapCfg := &zap.Config{
+		Level:             zap.NewAtomicLevelAt(cfg.Level),
+		Development:       cfg.Development,
+		Encoding:          cfg.Encoding,
+		EncoderConfig:     zap.NewProductionEncoderConfig(),
+		OutputPaths:       cfg.OutputPaths,
+		ErrorOutputPaths:  cfg.ErrorOutputPaths,
+		DisableCaller:     cfg.DisableCaller,
+		DisableStacktrace: cfg.DisableStacktrace,
+		InitialFields:     cfg.InitialFields,
+	}
+
+	if zapCfg.Encoding == "console" {
+		// Human-readable timestamps for console format of logs.
+		zapCfg.EncoderConfig.EncodeTime = zapcore.ISO8601TimeEncoder
+	}
+
+	logger, err := zapCfg.Build(options...)
+	if err != nil {
+		return nil, err
+	}
+	if cfg.Sampling != nil && cfg.Sampling.Enabled {
+		logger = newSampledLogger(logger, cfg.Sampling)
+	}
+
+	return logger, nil
+}
+
+func newSampledLogger(logger *zap.Logger, sc *LogsSamplingConfig) *zap.Logger {
+	// Create a logger that samples every Nth message after the first M messages every S seconds
+	// where N = sc.Thereafter, M = sc.Initial, S = sc.Tick.
+	opts := zap.WrapCore(func(core zapcore.Core) zapcore.Core {
+		return zapcore.NewSamplerWithOptions(
+			core,
+			sc.Tick,
+			sc.Initial,
+			sc.Thereafter,
+		)
+	})
+	return logger.WithOptions(opts)
+}