[improvement/server-graceful-shutdown] Add support of graceful shutdown (#312)

Dockerfile

@@ -78,7 +78,7 @@ COPY --from=builder /etc/ssl/certs /etc/ssl/certs
 RUN DEBIAN_FRONTEND=noninteractive \
   apt-get update && \
   apt-get install --no-install-recommends -y \
-  libglib2.0-0 libjpeg62-turbo libpng16-16 libopenexr23 \
+  procps libglib2.0-0 libjpeg62-turbo libpng16-16 libopenexr23 \
   libwebp6 libwebpmux3 libwebpdemux2 libtiff5 libgif7 libexif12 libxml2 libpoppler-glib8 \
   libmagickwand-6.q16-6 libpango1.0-0 libmatio4 libopenslide0 \
   libgsf-1-114 fftw3 liborc-0.4-0 librsvg2-2 libcfitsio7 libimagequant0 libheif1 && \

README.md

@@ -205,6 +205,16 @@ You can enable it simply passing a flag to the binary:
 $ imaginary -concurrency 20
 ```
 
+### Graceful shutdown
+
+When you use a cluster, it is necessary to control how the deployment is executed, and it is very useful to finish the containers in a controlled.
+
+You can use the next command:
+
+```
+$ ps auxw | grep 'bin/imaginary' | awk 'NR>1{print buf}{buf = $2}' | xargs kill -TERM > /dev/null 2>&1
+```
+
 ### Scalability
 
 If you're looking for a large scale solution for massive image processing, you should scale `imaginary` horizontally, distributing the HTTP load across a pool of imaginary servers.

imaginary.go

@@ -219,10 +219,7 @@ func main() {
 	LoadSources(opts)
 
 	// Start the server
-	err := Server(opts)
-	if err != nil {
-		exitWithError("cannot start the server: %s", err)
-	}
+	Server(opts)
 }
 
 func getPort(port int) int {

server.go

@@ -1,9 +1,13 @@
 package main
 
 import (
+	"context"
 	"net/http"
 	"net/url"
+	"log"
 	"os"
+	"os/signal"
+	"syscall"
 	"path"
 	"strconv"
 	"strings"
@@ -56,7 +60,7 @@ func (e Endpoints) IsValid(r *http.Request) bool {
 	return true
 }
 
-func Server(o ServerOptions) error {
+func Server(o ServerOptions) {
 	addr := o.Address + ":" + strconv.Itoa(o.Port)
 	handler := NewLog(NewServerMux(o), os.Stdout, o.LogLevel)
 
@@ -68,7 +72,27 @@ func Server(o ServerOptions) error {
 		WriteTimeout:   time.Duration(o.HTTPWriteTimeout) * time.Second,
 	}
 
-	return listenAndServe(server, o)
+	done := make(chan os.Signal, 1)
+	signal.Notify(done, os.Interrupt, syscall.SIGINT, syscall.SIGTERM)
+
+	go func() {
+		if err := listenAndServe(server, o); err != nil && err != http.ErrServerClosed {
+			log.Fatalf("listen: %s\n", err)
+		}
+	}()
+
+	<-done
+	log.Print("Graceful shutdown")
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer func() {
+		// extra handling here
+		cancel()
+	}()
+
+	if err := server.Shutdown(ctx); err != nil {
+		log.Fatalf("Server Shutdown Failed:%+v", err)
+	}
 }
 
 func listenAndServe(s *http.Server, o ServerOptions) error {