Add optional DataDog integration for telemetry and syslog forwarding

Forwards telemetry events as custom metrics (POST /api/v2/series) and
critical/high syslog entries as DataDog events (POST /api/v1/events)
via REST API — no DataDog Agent required. Completely inert when
DATADOG_API_KEY is not configured. Includes health check validation,
API call counting, and async buffered submission.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jonradoff

backend/cmd/server/main.go

@@ -27,6 +27,7 @@ import (
 	stripeservice "lastsaas/internal/stripe"
 	"lastsaas/internal/syslog"
 	"lastsaas/internal/telemetry"
+	"lastsaas/internal/datadog"
 	"lastsaas/internal/version"
 	"lastsaas/internal/webhooks"
 
@@ -140,6 +141,22 @@ func main() {
 
 	// Initialize system logger
 	sysLogger := syslog.New(database, cfgStore.Get)
+
+	// Initialize DataDog integration (optional)
+	var ddClient *datadog.Client
+	if cfg.DataDog.APIKey != "" {
+		site := cfg.DataDog.Site
+		if site == "" {
+			site = "us5.datadoghq.com"
+		}
+		ddClient = datadog.New(cfg.DataDog.APIKey, site, cfg.Environment, cfg.App.Name)
+		defer ddClient.Stop()
+		sysLogger.SetOnLog(ddClient.TrackSyslogEntry)
+		slog.Info("DataDog integration configured", "site", site)
+	} else {
+		slog.Warn("DataDog integration not configured", "reason", "missing API key")
+	}
+
 	sysLogger.Critical(context.Background(), fmt.Sprintf("System startup: LastSaaS v%s", version.Current))
 
 	// Initialize services
@@ -276,13 +293,21 @@ func main() {
 	} else {
 		healthService.RegisterIntegration("saml_sso", nil)
 	}
+	if ddClient != nil {
+		healthService.RegisterIntegration("datadog", health.NewDataDogChecker(ddClient))
+	} else {
+		healthService.RegisterIntegration("datadog", nil)
+	}
 
 	healthService.Start()
 	defer healthService.Stop()
 
 	// Initialize telemetry service
 	telemetrySvc := telemetry.New(database)
 	defer telemetrySvc.Stop()
+	if ddClient != nil {
+		telemetrySvc.SetOnTrack(ddClient.TrackTelemetryEvent)
+	}
 
 	// Initialize handlers
 	bootstrapHandler := handlers.NewBootstrapHandler(database)

backend/config/dev.example.yaml

@@ -35,3 +35,7 @@ stripe:
 
 webhooks:
   encryption_key: ${WEBHOOK_ENCRYPTION_KEY}
+
+datadog:
+  api_key: ${DATADOG_API_KEY}
+  site: ${DATADOG_SITE:us5.datadoghq.com}

backend/config/prod.example.yaml

@@ -36,3 +36,7 @@ stripe:
 
 webhooks:
   encryption_key: ${WEBHOOK_ENCRYPTION_KEY}
+
+datadog:
+  api_key: ${DATADOG_API_KEY}
+  site: ${DATADOG_SITE:us5.datadoghq.com}

backend/internal/apicounter/counter.go

@@ -7,6 +7,7 @@ import "sync/atomic"
 // snapshot/reset by the health collector every 60 seconds.
 
 var (
-	StripeAPICalls atomic.Int64
-	ResendEmails   atomic.Int64
+	StripeAPICalls  atomic.Int64
+	ResendEmails    atomic.Int64
+	DataDogAPICalls atomic.Int64
 )

backend/internal/config/config.go

@@ -22,6 +22,7 @@ type Config struct {
 	Stripe      StripeConfig     `yaml:"stripe"`
 	WebAuthn    WebAuthnConfig   `yaml:"webauthn"`
 	Webhooks    WebhooksConfig   `yaml:"webhooks"`
+	DataDog     DataDogConfig    `yaml:"datadog"`
 }
 
 type WebhooksConfig struct {
@@ -84,6 +85,11 @@ type StripeConfig struct {
 	WebhookSecret  string `yaml:"webhook_secret"`
 }
 
+type DataDogConfig struct {
+	APIKey string `yaml:"api_key"`
+	Site   string `yaml:"site"` // e.g. "us5.datadoghq.com"
+}
+
 // LoadEnvFile loads a .env file into the process environment if it exists.
 // It searches the current directory and up to 3 parent directories.
 func LoadEnvFile() {