Add OpenTelemetry instrumentation with middleware-only approach

pkg/config/config.go

@@ -11,16 +11,41 @@ import (
 
 // Config represents the application configuration
 type Config struct {
-	Server struct {
-		Host string `mapstructure:"host"`
-		Port int    `mapstructure:"port"`
-	}
-	Shutdown struct {
-		Timeout time.Duration `mapstructure:"timeout"`
-	}
-	Logging struct {
-		JSON bool `mapstructure:"json"`
-	}
+	Server    ServerConfig    `mapstructure:"server"`
+	Shutdown  ShutdownConfig  `mapstructure:"shutdown"`
+	Logging   LoggingConfig   `mapstructure:"logging"`
+	Telemetry TelemetryConfig `mapstructure:"telemetry"`
+}
+
+// ServerConfig holds server-related configuration
+type ServerConfig struct {
+	Host string `mapstructure:"host"`
+	Port int    `mapstructure:"port"`
+}
+
+// ShutdownConfig holds shutdown-related configuration
+type ShutdownConfig struct {
+	Timeout time.Duration `mapstructure:"timeout"`
+}
+
+// LoggingConfig holds logging-related configuration
+type LoggingConfig struct {
+	JSON bool `mapstructure:"json"`
+}
+
+// TelemetryConfig holds OpenTelemetry-related configuration
+type TelemetryConfig struct {
+	Enabled      bool          `mapstructure:"enabled"`
+	OTLPEndpoint string        `mapstructure:"otlp_endpoint"`
+	ServiceName  string        `mapstructure:"service_name"`
+	Insecure     bool          `mapstructure:"insecure"`
+	Sampler      SamplerConfig `mapstructure:"sampler"`
+}
+
+// SamplerConfig holds tracing sampler configuration
+type SamplerConfig struct {
+	Type  string  `mapstructure:"type"`
+	Ratio float64 `mapstructure:"ratio"`
 }
 
 // LoadConfig loads configuration from file, environment variables, and defaults
@@ -28,13 +53,21 @@ type Config struct {
 // To specify a custom config file path, set DLC_CONFIG_FILE environment variable
 func LoadConfig() (*Config, error) {
 	v := viper.New()
-	
+
 	// Set default values
 	v.SetDefault("server.host", "0.0.0.0")
 	v.SetDefault("server.port", 8080)
 	v.SetDefault("shutdown.timeout", 30*time.Second)
 	v.SetDefault("logging.json", false)
-	
+
+	// Telemetry defaults
+	v.SetDefault("telemetry.enabled", false)
+	v.SetDefault("telemetry.otlp_endpoint", "localhost:4317")
+	v.SetDefault("telemetry.service_name", "DanceLessonsCoach")
+	v.SetDefault("telemetry.insecure", true)
+	v.SetDefault("telemetry.sampler.type", "parentbased_always_on")
+	v.SetDefault("telemetry.sampler.ratio", 1.0)
+
 	// Check for custom config file path via environment variable
 	if configFile := os.Getenv("DLC_CONFIG_FILE"); configFile != "" {
 		v.SetConfigFile(configFile)
@@ -45,7 +78,7 @@ func LoadConfig() (*Config, error) {
 		v.SetConfigType("yaml")
 		v.AddConfigPath(".")
 	}
-	
+
 	// Read config file if it exists
 	if err := v.ReadInConfig(); err != nil {
 		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
@@ -56,7 +89,7 @@ func LoadConfig() (*Config, error) {
 	} else {
 		log.Info().Str("config_file", v.ConfigFileUsed()).Msg("Config file loaded")
 	}
-	
+
 	// Bind environment variables
 	v.AutomaticEnv()
 	v.SetEnvPrefix("DLC") // DanceLessonsCoach prefix
@@ -64,25 +97,65 @@ func LoadConfig() (*Config, error) {
 	v.BindEnv("server.port", "DLC_SERVER_PORT")
 	v.BindEnv("shutdown.timeout", "DLC_SHUTDOWN_TIMEOUT")
 	v.BindEnv("logging.json", "DLC_LOGGING_JSON")
-	
+
+	// Telemetry environment variables
+	v.BindEnv("telemetry.enabled", "DLC_TELEMETRY_ENABLED")
+	v.BindEnv("telemetry.otlp_endpoint", "DLC_TELEMETRY_OTLP_ENDPOINT")
+	v.BindEnv("telemetry.service_name", "DLC_TELEMETRY_SERVICE_NAME")
+	v.BindEnv("telemetry.insecure", "DLC_TELEMETRY_INSECURE")
+	v.BindEnv("telemetry.sampler.type", "DLC_TELEMETRY_SAMPLER_TYPE")
+	v.BindEnv("telemetry.sampler.ratio", "DLC_TELEMETRY_SAMPLER_RATIO")
+
 	// Unmarshal into Config struct
 	var config Config
 	if err := v.Unmarshal(&config); err != nil {
 		log.Error().Err(err).Msg("Failed to unmarshal config")
 		return nil, fmt.Errorf("config unmarshal error: %w", err)
 	}
-	
+
 	log.Info().
 		Str("host", config.Server.Host).
 		Int("port", config.Server.Port).
 		Dur("shutdown_timeout", config.Shutdown.Timeout).
 		Bool("logging_json", config.Logging.JSON).
+		Bool("telemetry_enabled", config.Telemetry.Enabled).
+		Str("telemetry_service", config.Telemetry.ServiceName).
 		Msg("Configuration loaded")
-	
+
 	return &config, nil
 }
 
 // GetServerAddress returns the formatted server address (host:port)
 func (c *Config) GetServerAddress() string {
 	return fmt.Sprintf("%s:%d", c.Server.Host, c.Server.Port)
-}
+}
+
+// GetTelemetryEnabled returns whether telemetry is enabled
+func (c *Config) GetTelemetryEnabled() bool {
+	return c.Telemetry.Enabled
+}
+
+// GetOTLPEndpoint returns the OTLP endpoint for telemetry
+func (c *Config) GetOTLPEndpoint() string {
+	return c.Telemetry.OTLPEndpoint
+}
+
+// GetServiceName returns the service name for telemetry
+func (c *Config) GetServiceName() string {
+	return c.Telemetry.ServiceName
+}
+
+// GetTelemetryInsecure returns whether to use insecure connection
+func (c *Config) GetTelemetryInsecure() bool {
+	return c.Telemetry.Insecure
+}
+
+// GetSamplerType returns the sampler type
+func (c *Config) GetSamplerType() string {
+	return c.Telemetry.Sampler.Type
+}
+
+// GetSamplerRatio returns the sampler ratio
+func (c *Config) GetSamplerRatio() float64 {
+	return c.Telemetry.Sampler.Ratio
+}