Add graceful gRPC server example

README.md

@@ -46,6 +46,7 @@ if err := upg.Ready(); err != nil {
 ```
 
 Please see the more elaborate [graceful shutdown with net/http](http_example_test.go) example.
+For gRPC servers, see the [graceful gRPC server example](examples/grpc-server).
 
 ## Integration with `systemd`
 

examples/grpc-server/README.md

@@ -0,0 +1,24 @@
+# Graceful gRPC server upgrades
+
+This example transfers the listening socket to a new process while the old gRPC server finishes its active RPCs. It registers the standard gRPC health service and server reflection, so no generated service code is required.
+
+Build and start the server:
+
+```sh
+go build -o tableflip-grpc .
+./tableflip-grpc -pid-file ./tableflip-grpc.pid
+```
+
+With [`grpcurl`](https://github.com/fullstorydev/grpcurl) installed, check the server:
+
+```sh
+grpcurl -plaintext localhost:8080 grpc.health.v1.Health/Check
+```
+
+Start an upgrade by sending `SIGHUP` to the current process:
+
+```sh
+kill -HUP "$(cat tableflip-grpc.pid)"
+```
+
+The replacement process inherits the listening socket and calls `Ready` before the old process stops accepting connections. The old gRPC server then calls `GracefulStop`, which lets active RPCs finish. If they do not finish within `-shutdown-timeout`, the server calls `Stop` and terminates them.

examples/grpc-server/go.mod

@@ -0,0 +1,10 @@
+module github.com/cloudflare/tableflip/examples/grpc-server
+
+go 1.14
+
+require (
+	github.com/cloudflare/tableflip v0.0.0
+	google.golang.org/grpc v1.45.0
+)
+
+replace github.com/cloudflare/tableflip => ../..

examples/grpc-server/go.sum

@@ -0,0 +1,121 @@
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+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
+honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=

examples/grpc-server/main.go

@@ -0,0 +1,104 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"github.com/cloudflare/tableflip"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/health"
+	healthpb "google.golang.org/grpc/health/grpc_health_v1"
+	"google.golang.org/grpc/reflection"
+)
+
+var (
+	listenAddr      = flag.String("listen", "localhost:8080", "address to listen on")
+	pidFile         = flag.String("pid-file", "", "path to the tableflip PID file")
+	shutdownTimeout = flag.Duration("shutdown-timeout", 30*time.Second, "maximum time to drain active RPCs")
+)
+
+func main() {
+	flag.Parse()
+	log.SetPrefix(fmt.Sprintf("%d ", os.Getpid()))
+
+	upg, err := tableflip.New(tableflip.Options{PIDFile: *pidFile})
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer upg.Stop()
+
+	go upgradeOnSignal(upg)
+
+	ln, err := upg.Listen("tcp", *listenAddr)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	server := grpc.NewServer()
+	healthServer := health.NewServer()
+	healthServer.SetServingStatus("", healthpb.HealthCheckResponse_SERVING)
+	healthpb.RegisterHealthServer(server, healthServer)
+	reflection.Register(server)
+
+	serveErr := make(chan error, 1)
+	go func() {
+		serveErr <- server.Serve(ln)
+	}()
+
+	if err := upg.Ready(); err != nil {
+		log.Fatal(err)
+	}
+	log.Printf("serving gRPC on %s", *listenAddr)
+
+	select {
+	case <-upg.Exit():
+		healthServer.SetServingStatus("", healthpb.HealthCheckResponse_NOT_SERVING)
+		if !gracefulStop(server, *shutdownTimeout) {
+			log.Printf("graceful shutdown timed out after %s; stopped active RPCs", *shutdownTimeout)
+		}
+	case err := <-serveErr:
+		if err != nil {
+			log.Fatal(err)
+		}
+	}
+}
+
+func upgradeOnSignal(upg *tableflip.Upgrader) {
+	signals := make(chan os.Signal, 1)
+	signal.Notify(signals, syscall.SIGHUP)
+	for range signals {
+		if err := upg.Upgrade(); err != nil {
+			log.Printf("upgrade failed: %v", err)
+		}
+	}
+}
+
+type gracefulServer interface {
+	GracefulStop()
+	Stop()
+}
+
+// gracefulStop waits for active RPCs and force-stops them after the deadline.
+func gracefulStop(server gracefulServer, timeout time.Duration) bool {
+	done := make(chan struct{})
+	go func() {
+		server.GracefulStop()
+		close(done)
+	}()
+
+	timer := time.NewTimer(timeout)
+	defer timer.Stop()
+
+	select {
+	case <-done:
+		return true
+	case <-timer.C:
+		server.Stop()
+		return false
+	}
+}

examples/grpc-server/main_test.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+type testServer struct {
+	releaseGraceful chan struct{}
+	stopCalled      chan struct{}
+	stopOnce        sync.Once
+}
+
+func newTestServer() *testServer {
+	return &testServer{
+		releaseGraceful: make(chan struct{}),
+		stopCalled:      make(chan struct{}),
+	}
+}
+
+func (server *testServer) GracefulStop() {
+	<-server.releaseGraceful
+}
+
+func (server *testServer) Stop() {
+	server.stopOnce.Do(func() {
+		close(server.stopCalled)
+		close(server.releaseGraceful)
+	})
+}
+
+func TestGracefulStopCompletesBeforeDeadline(t *testing.T) {
+	server := newTestServer()
+	close(server.releaseGraceful)
+
+	if !gracefulStop(server, time.Second) {
+		t.Fatal("expected graceful shutdown")
+	}
+
+	select {
+	case <-server.stopCalled:
+		t.Fatal("Stop called after GracefulStop completed")
+	default:
+	}
+}
+
+func TestGracefulStopForcesShutdownAtDeadline(t *testing.T) {
+	server := newTestServer()
+
+	if gracefulStop(server, time.Millisecond) {
+		t.Fatal("expected forced shutdown")
+	}
+
+	select {
+	case <-server.stopCalled:
+	default:
+		t.Fatal("Stop was not called")
+	}
+}