Move tracing to plugin

This just makes the implementation a little cleaner.
It also makes the trace exporter pluggable.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

tracing/tracing.go

@@ -19,87 +19,17 @@ package tracing
 import (
 	"context"
 
-	srvconfig "github.com/containerd/containerd/services/server/config"
-	"github.com/pkg/errors"
-	"github.com/sirupsen/logrus"
 	"go.opentelemetry.io/otel"
-	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc"
-	"go.opentelemetry.io/otel/propagation"
-	"go.opentelemetry.io/otel/sdk/resource"
-	sdktrace "go.opentelemetry.io/otel/sdk/trace"
-	semconv "go.opentelemetry.io/otel/semconv/v1.4.0"
 	"go.opentelemetry.io/otel/trace"
-	"google.golang.org/grpc"
 )
 
-// InitOpenTelemetry reads config and initializes otel middleware, sets the exporter
-// propagator and global tracer provider
-func InitOpenTelemetry(config *srvconfig.Config) (func(), error) {
-	ctx := context.Background()
-
-	// Check if tracing is configured
-	if config.OpenTelemetry == (srvconfig.OpenTelemetryConfig{}) {
-		logrus.Info("OpenTelemetry configuration not found, tracing is disabled")
-		return nil, nil
-	}
-
-	// Validate configuration
-	if err := config.OpenTelemetry.Validate(); err != nil {
-		return nil, errors.Wrap(err, "invalid open telemetry configuration")
-	}
-
-	res, err := resource.New(ctx,
-		resource.WithAttributes(
-			// Service name used to displace traces in backends
-			semconv.ServiceNameKey.String(config.OpenTelemetry.ServiceName),
-		),
-	)
-	if err != nil {
-		return nil, errors.Wrap(err, "failed to create resource")
-	}
-
-	// Configure OTLP trace exporter and set it up to connect to OpenTelemetry collector
-	// running on a local host.
-	ctrdTraceExporter, err := otlptracegrpc.New(ctx,
-		otlptracegrpc.WithEndpoint(config.OpenTelemetry.ExporterEndpoint),
-		otlptracegrpc.WithDialOption(grpc.WithBlock()),
-	)
-	if err != nil {
-		return nil, errors.Wrap(err, "failed to create trace exporter")
-	}
-
-	// Register the trace exporter with a TracerProvider, using a batch span
-	// process to aggregate spans before export.
-	ctrdBatchSpanProcessor := sdktrace.NewBatchSpanProcessor(ctrdTraceExporter)
-	ctrdTracerProvider := sdktrace.NewTracerProvider(
-		// We use TraceIDRatioBased sampling. Ratio read from config translated into following
-		// if sampling ratio < 0 it is interpreted as 0. If ratio >= 1, it will always sample.
-		sdktrace.WithSampler(sdktrace.TraceIDRatioBased(config.OpenTelemetry.TraceSamplingRatio)),
-		sdktrace.WithResource(res),
-		sdktrace.WithSpanProcessor(ctrdBatchSpanProcessor),
-	)
-	otel.SetTracerProvider(ctrdTracerProvider)
-
-	// set global propagator to tracecontext
-	otel.SetTextMapPropagator(propagation.TraceContext{})
-
-	return func() {
-		// Shutdown will flush any remaining spans and shut down the exporter.
-		err := ctrdTracerProvider.Shutdown(ctx)
-		if err != nil {
-			logrus.WithError(err).Errorf("failed to shutdown TracerProvider")
-		}
-	}, nil
-}
-
 // StartSpan starts child span in a context.
 func StartSpan(ctx context.Context, opName string, opts ...trace.SpanStartOption) (trace.Span, context.Context) {
-	parentSpan := trace.SpanFromContext(ctx)
-	tracer := trace.NewNoopTracerProvider().Tracer("")
-	if parentSpan.SpanContext().IsValid() {
-		tracer = parentSpan.TracerProvider().Tracer("")
+	if parent := trace.SpanFromContext(ctx); parent != nil && parent.SpanContext().IsValid() {
+		ctx, span := parent.TracerProvider().Tracer("").Start(ctx, opName, opts...)
+		return span, ctx
 	}
-	ctx, span := tracer.Start(ctx, opName, opts...)
+	ctx, span := otel.Tracer("").Start(ctx, opName, opts...)
 	return span, ctx
 }