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/utils/otel/provider.go

@@ -216,11 +216,11 @@ func InitProvider(ctx context.Context, logger *zap.Logger, serviceName string) (
 	return func(ctx context.Context) {
 		err := tracerProvider.Shutdown(ctx)
 		if err != nil && logger != nil {
-			logger.Fatal("error shutting down trace provider", zap.Error(err))
+			logger.Error("error shutting down trace provider", zap.Error(err))
 		}
 		if traceExporter != nil {
 			if err = traceExporter.Shutdown(ctx); err != nil && logger != nil {
-				logger.Fatal("error shutting down trace exporter", zap.Error(err))
+				logger.Error("error shutting down trace exporter", zap.Error(err))
 			}
 		}
 	}, nil

pkg/utils/signals/signals.go

@@ -0,0 +1,46 @@
+/*
+Copyright 2021 The Fission Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+package signals
+
+import (
+	"context"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"go.uber.org/zap"
+)
+
+var onlyOneSignalHandler = make(chan struct{})
+
+func SetupSignalHandlerWithContext(logger *zap.Logger) context.Context {
+	var shutdownSignals = []os.Signal{os.Interrupt, syscall.SIGTERM}
+
+	close(onlyOneSignalHandler) // panics when called twice
+
+	ctx, cancel := context.WithCancel(context.Background())
+	c := make(chan os.Signal, 2)
+	signal.Notify(c, shutdownSignals...)
+	go func() {
+		signal := <-c
+		logger.Info("Received signal", zap.String("signal", signal.String()))
+		cancel()
+		<-c
+		panic("multiple signals received")
+	}()
+
+	return ctx
+}