opentracing support

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

cmd/dagger/logger/tracer.go

@@ -0,0 +1,36 @@
+package logger
+
+import (
+	"io"
+	"os"
+
+	opentracing "github.com/opentracing/opentracing-go"
+	jaeger "github.com/uber/jaeger-client-go"
+)
+
+func InitTracing() io.Closer {
+	traceAddr := os.Getenv("JAEGER_TRACE")
+	if traceAddr == "" {
+		return &nopCloser{}
+	}
+
+	tr, err := jaeger.NewUDPTransport(traceAddr, 0)
+	if err != nil {
+		panic(err)
+	}
+
+	tracer, closer := jaeger.NewTracer(
+		"dagger",
+		jaeger.NewConstSampler(true),
+		jaeger.NewRemoteReporter(tr),
+	)
+	opentracing.SetGlobalTracer(tracer)
+	return closer
+}
+
+type nopCloser struct {
+}
+
+func (*nopCloser) Close() error {
+	return nil
+}