Add support to gracefully shutdown the server

This is done by draining the connections for configured time after registry receives a SIGTERM signal.
This adds a `draintimeout` setting under `HTTP`. Registry doesn't drain
if draintimeout is not provided.

Signed-off-by: Manish Tomar <manish.tomar@docker.com>

configuration/configuration.go

@@ -84,6 +84,10 @@ type Configuration struct {
 		// Location headers
 		RelativeURLs bool `yaml:"relativeurls,omitempty"`
 
+		// Amount of time to wait for connection to drain before shutting down when registry
+		// receives a stop signal
+		DrainTimeout time.Duration `yaml:"draintimeout,omitempty"`
+
 		// TLS instructs the http server to listen with a TLS configuration.
 		// This only support simple tls configuration with a cert and key.
 		// Mostly, this is useful for testing situations or simple deployments

configuration/configuration_test.go

@@ -7,6 +7,7 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 
 	. "gopkg.in/check.v1"
 	"gopkg.in/yaml.v2"
@@ -77,6 +78,7 @@ var configStruct = Configuration{
 		Prefix       string        `yaml:"prefix,omitempty"`
 		Secret       string        `yaml:"secret,omitempty"`
 		RelativeURLs bool          `yaml:"relativeurls,omitempty"`
+		DrainTimeout time.Duration `yaml:"draintimeout,omitempty"`
 		TLS          struct {
 			Certificate string   `yaml:"certificate,omitempty"`
 			Key         string   `yaml:"key,omitempty"`

docs/configuration.md

@@ -206,6 +206,7 @@ http:
   host: https://myregistryaddress.org:5000
   secret: asecretforlocaldevelopment
   relativeurls: false
+  draintimeout: 60s
   tls:
     certificate: /path/to/x509/public
     key: /path/to/x509/private
@@ -738,6 +739,7 @@ http:
   host: https://myregistryaddress.org:5000
   secret: asecretforlocaldevelopment
   relativeurls: false
+  draintimeout: 60s
   tls:
     certificate: /path/to/x509/public
     key: /path/to/x509/private
@@ -767,6 +769,7 @@ registry.
 | `host`    | no       | A fully-qualified URL for an externally-reachable address for the registry. If present, it is used when creating generated URLs. Otherwise, these URLs are derived from client requests. |
 | `secret`  | no       | A random piece of data used to sign state that may be stored with the client to protect against tampering. For production environments you should generate a random piece of data using a cryptographically secure random generator. If you omit the secret, the registry will automatically generate a secret when it starts. **If you are building a cluster of registries behind a load balancer, you MUST ensure the secret is the same for all registries.**|
 | `relativeurls`| no    | If `true`,  the registry returns relative URLs in Location headers. The client is responsible for resolving the correct URL. **This option is not compatible with Docker 1.7 and earlier.**|
+| `draintimeout`| no    | Amount of time to wait for HTTP connections to drain before shutting after registry receives SIGTERM signal|
 
 
 ### `tls`

registry/registry.go

@@ -8,6 +8,8 @@ import (
 	"io/ioutil"
 	"net/http"
 	"os"
+	"os/signal"
+	"syscall"
 	"time"
 
 	"rsc.io/letsencrypt"
@@ -28,6 +30,9 @@ import (
 	"github.com/yvasiyarov/gorelic"
 )
 
+// this channel gets notified when process receives signal. It is global to ease unit testing
+var quit = make(chan os.Signal, 1)
+
 // ServeCmd is a cobra command for running the registry.
 var ServeCmd = &cobra.Command{
 	Use:   "serve <config>",
@@ -195,7 +200,29 @@ func (registry *Registry) ListenAndServe() error {
 		dcontext.GetLogger(registry.app).Infof("listening on %v", ln.Addr())
 	}
 
+	if config.HTTP.DrainTimeout == 0 {
 		return registry.server.Serve(ln)
+	}
+
+	// setup channel to get notified on SIGTERM signal
+	signal.Notify(quit, syscall.SIGTERM)
+	serveErr := make(chan error)
+
+	// Start serving in goroutine and listen for stop signal in main thread
+	go func() {
+		serveErr <- registry.server.Serve(ln)
+	}()
+
+	select {
+	case err := <-serveErr:
+		return err
+	case <-quit:
+		dcontext.GetLogger(registry.app).Info("stopping server gracefully. Draining connections for ", config.HTTP.DrainTimeout)
+		// shutdown the server with a grace period of configured timeout
+		c, cancel := context.WithTimeout(context.Background(), config.HTTP.DrainTimeout)
+		defer cancel()
+		return registry.server.Shutdown(c)
+	}
 }
 
 func configureReporting(app *handlers.App) http.Handler {

registry/registry_test.go

@@ -1,10 +1,19 @@
 package registry
 
 import (
+	"bufio"
+	"context"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"os"
 	"reflect"
 	"testing"
+	"time"
 
 	"github.com/docker/distribution/configuration"
+	_ "github.com/docker/distribution/registry/storage/driver/inmemory"
 )
 
 // Tests to ensure nextProtos returns the correct protocols when:
@@ -28,3 +37,64 @@ func TestNextProtos(t *testing.T) {
 		t.Fatalf("expected protos to equal [http/1.1], got %s", protos)
 	}
 }
+
+func setupRegistry() (*Registry, error) {
+	config := &configuration.Configuration{}
+	// TODO: this needs to change to something ephemeral as the test will fail if there is any server
+	// already listening on port 5000
+	config.HTTP.Addr = ":5000"
+	config.HTTP.DrainTimeout = time.Duration(10) * time.Second
+	config.Storage = map[string]configuration.Parameters{"inmemory": map[string]interface{}{}}
+	return NewRegistry(context.Background(), config)
+}
+
+func TestGracefulShutdown(t *testing.T) {
+	registry, err := setupRegistry()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// run registry server
+	var errchan chan error
+	go func() {
+		errchan <- registry.ListenAndServe()
+	}()
+	select {
+	case err = <-errchan:
+		t.Fatalf("Error listening: %v", err)
+	default:
+	}
+
+	// Wait for some unknown random time for server to start listening
+	time.Sleep(3 * time.Second)
+
+	// send incomplete request
+	conn, err := net.Dial("tcp", "localhost:5000")
+	if err != nil {
+		t.Fatal(err)
+	}
+	fmt.Fprintf(conn, "GET /v2/ ")
+
+	// send stop signal
+	quit <- os.Interrupt
+	time.Sleep(100 * time.Millisecond)
+
+	// try connecting again. it shouldn't
+	_, err = net.Dial("tcp", "localhost:5000")
+	if err == nil {
+		t.Fatal("Managed to connect after stopping.")
+	}
+
+	// make sure earlier request is not disconnected and response can be received
+	fmt.Fprintf(conn, "HTTP/1.1\r\nHost: 127.0.0.1\r\n\r\n")
+	resp, err := http.ReadResponse(bufio.NewReader(conn), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resp.Status != "200 OK" {
+		t.Error("response status is not 200 OK: ", resp.Status)
+	}
+	if body, err := ioutil.ReadAll(resp.Body); err != nil || string(body) != "{}" {
+		t.Error("Body is not {}; ", string(body))
+	}
+}