Add support for tracing via OpenCencus

This adds a few flags for configuring the tracer.
Includes support for jaeger tracing (built into OC).

cmd/cencus_jaeger.go

@@ -0,0 +1,36 @@
+// +build !no_jaeger_exporter
+
+package cmd
+
+import (
+	"errors"
+	"os"
+
+	"go.opencensus.io/exporter/jaeger"
+	"go.opencensus.io/trace"
+)
+
+func init() {
+	RegisterTracingExporter("jaeger", NewJaegerExporter)
+}
+
+func NewJaegerExporter(opts TracingExporterOptions) (trace.Exporter, error) {
+	jOpts := jaeger.Options{
+		Endpoint:      os.Getenv("JAEGER_ENDPOINT"),
+		AgentEndpoint: os.Getenv("JAEGER_AGENT_ENDPOINT"),
+		Username:      os.Getenv("JAEGER_USER"),
+		Password:      os.Getenv("JAEGER_PASSWORD"),
+		Process: jaeger.Process{
+			ServiceName: opts.ServiceName,
+		},
+	}
+
+	if jOpts.Endpoint == "" && jOpts.AgentEndpoint == "" {
+		return nil, errors.New("Must specify either JAEGER_ENDPOINT or JAEGER_AGENT_ENDPOINT")
+	}
+
+	for k, v := range opts.Tags {
+		jOpts.Process.Tags = append(jOpts.Process.Tags, jaeger.StringTag(k, v))
+	}
+	return jaeger.NewExporter(jOpts)
+}