Capture os signals to gracefully shutdown fission components (#2261)

- Currently, fission components don't handle shutdown signals.
So we don't get any to do the required cleanup before the fission process
exits. Adding signal capture process with cancelling context so
that all dependent processes stop working when the process gets term
signal.
- Set log level to error in otel shutdown function

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/router/router.go

@@ -126,7 +126,7 @@ func serveMetric(logger *zap.Logger) {
 }
 
 // Start starts a router
-func Start(logger *zap.Logger, port int, executorURL string, openTracingEnabled bool) {
+func Start(ctx context.Context, logger *zap.Logger, port int, executorURL string, openTracingEnabled bool) {
 	fmap := makeFunctionServiceMap(logger, time.Minute)
 
 	fissionClient, kubeClient, _, _, err := crd.MakeFissionClient()
@@ -258,10 +258,8 @@ func Start(logger *zap.Logger, port int, executorURL string, openTracingEnabled
 	logger.Info("starting router", zap.Int("port", port))
 
 	tracer := otel.Tracer("router")
-	ctx, span := tracer.Start(context.Background(), "router/Start")
+	ctx, span := tracer.Start(ctx, "router/Start")
 	defer span.End()
 
-	ctxWithCancel, cancel := context.WithCancel(ctx)
-	defer cancel()
-	serve(ctxWithCancel, logger, port, tracingSamplingRate, triggers, displayAccessLog, openTracingEnabled)
+	serve(ctx, logger, port, tracingSamplingRate, triggers, displayAccessLog, openTracingEnabled)
 }