cogolabs/terminator

Author: jcalabro

README.md

@@ -0,0 +1,53 @@
+# Terminator
+
+<img src="https://user-images.githubusercontent.com/8205547/162049312-28e505f3-100c-47b4-a168-78d4ff9dd19f.jpg" />
+
+Library to automatically run and kill HTTP servers at regular intervals. Includes a jitter on the kill interval to ensure that a group of server processes started at roughly the same time don't all go down at once.
+
+## Usage:
+
+```go
+package main
+
+import (
+	"flag"
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/cogolabs/terminator"
+)
+
+const (
+	timeout = 30 * time.Second
+)
+
+var (
+	shutdownAfter  = flag.Duration("shutdownAfter", 12*time.Hour, "Duration to wait before shutting down (with jitter)")
+	shutdownJitter = flag.Duration("shutdownJitter", 2*time.Hour, "Jitter duration in either direction of shutdownAfter")
+)
+
+func main() {
+	flag.Parse()
+
+	srv := &http.Server{
+		Addr:         "0.0.0.0:8080",
+		Handler:      nil, // your handler here
+		ReadTimeout:  timeout,
+		WriteTimeout: timeout,
+	}
+
+	log.Println("starting server")
+	err := terminator.ServeAndShutdownAfter(&terminator.Options{
+		Server:                 srv,
+		ShutdownAfter:          *shutdownAfter,
+		Jitter:                 *shutdownJitter,
+		GracefulShutdownPeriod: 30 * time.Second,
+	})
+	if err != nil {
+		log.Fatalf("error in server: %v\n", err)
+	}
+
+	log.Println("server done")
+}
+```

terminator.go

@@ -0,0 +1,75 @@
+package terminator
+
+import (
+	"context"
+	"math/rand"
+	"net/http"
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+	"time"
+)
+
+type Options struct {
+	// Server is the HTTP server that will be started and eventually
+	// gracefully shut down
+	Server *http.Server
+
+	// ShutdownAfter indicates how long we should keep the HTTP
+	// server alive before starting to shutdown
+	ShutdownAfter time.Duration
+
+	// Jitter represents a random offset in either direction of
+	// ShutdownAfter that we'll add to ShutdownAfter. This ensures
+	// that not all servers go down at once, thus avoiding outages.
+	Jitter time.Duration
+
+	// GracefulShutdownPeriod represents the maximum amount of time
+	// we allow in-flight requests to finish before we force shutdown
+	GracefulShutdownPeriod time.Duration
+}
+
+// ServeAndShutdownAfter starts the given HTTP server, waits for the given shutdownAfter duration,
+// then gracefully shuts the server down and returns to the caller. The maximum amount of time
+// in-progress requests are given is represented by gracefulShutdownTimeout.
+func ServeAndShutdownAfter(opts *Options) error {
+	sig := make(chan os.Signal, 1)
+	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
+
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+
+	go func() {
+		defer wg.Done()
+
+		// add a random jitter in the range of (-n, n) seconds to the max shutdown
+		// time to ensure not all servers in a deployment go down at the same time
+		rng := rand.New(rand.NewSource(time.Now().UnixNano()))
+		jitterSecs := int(opts.Jitter.Seconds())
+		offset := rng.Intn(2*jitterSecs) - jitterSecs
+		offsetSecs := time.Second * time.Duration(offset)
+		waitFor := opts.ShutdownAfter + offsetSecs
+
+		// wait for a SIGINT to arrive or for the wait duration to elapse
+		select {
+		case <-sig:
+		case <-time.After(waitFor):
+		}
+
+		ctx, cancel := context.WithTimeout(context.Background(), opts.GracefulShutdownPeriod)
+		defer cancel()
+
+		// gracefully shut down the server
+		opts.Server.SetKeepAlivesEnabled(false)
+		opts.Server.Shutdown(ctx)
+	}()
+
+	err := opts.Server.ListenAndServe()
+	if err != nil && err != http.ErrServerClosed {
+		return err
+	}
+
+	wg.Wait()
+	return nil
+}