Fission meets OpenTelemetry (#2157)

* add opentracing section and otelCollectorEndpoint
* initialize OTLP exporter
* pkg/controller: changes for context propagation
* pkg/executor: changes for context propagation
* pkg/fetcher: changes for context propagation
* pkg/router: changes for context propagation
* pkg/storagesvc: changes for context propagation
* set no default value for otel collector endpoint
* update readme and add notes to charts
* move common code to pkg/utils/otel
* adding fn and env as attributes
* don't use otelhttp transport for websocket
* URL ignore with common filter UrlsToIgnore

Note: The web socket example does not work when using OTEL HTTP. Here is an issue related to that on open-telemetry/opentelemetry-js-contrib.

Signed-off-by: Gaurav Gahlot <gauravgahlot0107@gmail.com>
Co-authored-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/utils/tracing/tracing.go

@@ -0,0 +1,45 @@
+package tracing
+
+import (
+	"os"
+	"strconv"
+	"strings"
+
+	"contrib.go.opencensus.io/exporter/jaeger"
+	"go.opencensus.io/trace"
+	"go.uber.org/zap"
+)
+
+func RegisterTraceExporter(logger *zap.Logger, collectorEndpoint, serviceName string) error {
+	if len(collectorEndpoint) == 0 {
+		logger.Info("skipping trace exporter registration")
+		return nil
+	}
+
+	exporter, err := jaeger.NewExporter(jaeger.Options{
+		CollectorEndpoint: collectorEndpoint,
+		Process: jaeger.Process{
+			ServiceName: serviceName,
+			Tags: []jaeger.Tag{
+				jaeger.BoolTag("fission", true),
+			},
+		},
+	})
+	if err != nil {
+		return err
+	}
+
+	trace.RegisterExporter(exporter)
+
+	if strings.EqualFold(serviceName, "Fission-Fetcher") {
+		trace.ApplyConfig(trace.Config{DefaultSampler: trace.AlwaysSample()})
+	} else {
+		samplingRate, err := strconv.ParseFloat(os.Getenv("TRACING_SAMPLING_RATE"), 32)
+		if err != nil {
+			return err
+		}
+		trace.ApplyConfig(trace.Config{DefaultSampler: trace.ProbabilitySampler(samplingRate)})
+	}
+
+	return nil
+}