fix(tracing): record error on mux (#304)

The otellambda wrapper does not record an error when the invoked lambda
fails. We need to do it ourselves for now, otherwise the respective KPIs
will be skewed.

pkg/tracing/mux.go

@@ -6,6 +6,7 @@ import (
 	"github.com/aws/aws-lambda-go/lambda"
 	"go.opentelemetry.io/contrib/instrumentation/github.com/aws/aws-lambda-go/otellambda"
 	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
 	"go.opentelemetry.io/otel/trace"
 )
@@ -27,6 +28,14 @@ type LambdaHandler struct {
 func (h *LambdaHandler) Invoke(ctx context.Context, payload []byte) ([]byte, error) {
 	span := trace.SpanFromContext(ctx)
 	span.SetAttributes(payloadKey.String(string(payload)))
+	resp, err := h.Handler.Invoke(ctx, payload)
+
+	// surprisingly, otellambda wrapper does not emit the error
+	if err != nil {
+		span.RecordError(err)
+		span.SetStatus(codes.Error, err.Error())
+	}
+
 	// nolint: wrapcheck
-	return h.Handler.Invoke(ctx, payload)
+	return resp, err
 }