Allow to queue API requests and limit given capacity

Expose three options to configure queueing limits:
- apiLimit
- apiQueueLimit
- apiQueueTimeout

internal/helper/helpers.go

@@ -21,6 +21,18 @@ func LogError(r *http.Request, err error) {
 	printError(r, err)
 }
 
+func ServiceUnavailable(w http.ResponseWriter, r *http.Request, err error) {
+	http.Error(w, "Service Unavailable", http.StatusServiceUnavailable)
+	captureRavenError(r, err)
+	printError(r, err)
+}
+
+func TooManyRequests(w http.ResponseWriter, r *http.Request, err error) {
+	http.Error(w, "Too Many Requests", http.StatusTooManyRequests)
+	captureRavenError(r, err)
+	printError(r, err)
+}
+
 func printError(r *http.Request, err error) {
 	if r != nil {
 		log.Printf("error: %s %q: %v", r.Method, r.RequestURI, err)

internal/queueing/queue.go

+package queueing
+
+import (
+	"errors"
+	"time"
+)
+
+type errTooManyRequests struct{ error }
+type errQueueingTimedout struct{ error }
+
+var ErrTooManyRequests = &errTooManyRequests{errors.New("too many requests queued")}
+var ErrQueueingTimedout = &errQueueingTimedout{errors.New("queueing timedout")}
+
+type Queue struct {
+	busyCh    chan struct{}
+	waitingCh chan struct{}
+}
+
+// NewQueue creates a new queue
+// limit specifies number of requests run concurrently
+// queueLimit specifies maximum number of requests that can be queued
+// if the number of requests is above the limit
+func NewQueue(limit, queueLimit int) *Queue {
+	return &Queue{
+		busyCh:    make(chan struct{}, limit),
+		waitingCh: make(chan struct{}, queueLimit),
+	}
+}
+
+// Acquire takes one slot from the Queue
+// and returns when a request should be processed
+// it allows up to (limit) of requests running at a time
+// it allows to queue up to (queue-limit) requests
+func (s *Queue) Acquire(timeout time.Duration) (err error) {
+	// push item to a queue to claim your own slot (non-blocking)
+	select {
+	case s.waitingCh <- struct{}{}:
+		break
+	default:
+		return ErrTooManyRequests
+	}
+
+	defer func() {
+		if err != nil {
+			<-s.waitingCh
+		}
+	}()
+
+	// fast path: push item to current processed items (non-blocking)
+	select {
+	case s.busyCh <- struct{}{}:
+		return nil
+	default:
+		break
+	}
+
+	timer := time.NewTimer(timeout)
+	defer timer.Stop()
+
+	// push item to current processed items (blocking)
+	select {
+	case s.busyCh <- struct{}{}:
+		return nil
+
+	case <-timer.C:
+		return ErrQueueingTimedout
+	}
+}
+
+// Release marks the finish of processing of requests
+// It triggers next request to be processed if it's in queue
+func (s *Queue) Release() {
+	// dequeue from queue to allow next request to be processed
+	<-s.waitingCh
+	<-s.busyCh
+}

internal/queueing/queue_test.go

+package queueing_test
+
+import (
+	"testing"
+	"time"
+
+	. "gitlab.com/gitlab-org/gitlab-workhorse/internal/queueing"
+)
+
+func TestNormalQueueing(t *testing.T) {
+	q := NewQueue(2, 3)
+	err1 := q.Acquire(time.Microsecond)
+	if err1 != nil {
+		t.Fatal("we should acquire a new slot")
+	}
+
+	err2 := q.Acquire(time.Microsecond)
+	if err2 != nil {
+		t.Fatal("we should acquire a new slot")
+	}
+
+	err3 := q.Acquire(time.Microsecond)
+	if err3 != ErrQueueingTimedout {
+		t.Fatal("we should timeout")
+	}
+
+	q.Release()
+
+	err4 := q.Acquire(time.Microsecond)
+	if err4 != nil {
+		t.Fatal("we should acquire a new slot")
+	}
+}
+
+func TestQueueLimit(t *testing.T) {
+	q := NewQueue(1, 1)
+	err1 := q.Acquire(time.Microsecond)
+	if err1 != nil {
+		t.Fatal("we should acquire a new slot")
+	}
+
+	err2 := q.Acquire(time.Microsecond)
+	if err2 != ErrTooManyRequests {
+		t.Fatal("we should fail because of not enough slots in queue")
+	}
+}
+
+func TestQueueProcessing(t *testing.T) {
+	q := NewQueue(1, 2)
+	err1 := q.Acquire(time.Microsecond)
+	if err1 != nil {
+		t.Fatal("we should acquire a new slot")
+	}
+
+	go func() {
+		time.Sleep(50 * time.Microsecond)
+		q.Release()
+	}()
+
+	err2 := q.Acquire(time.Second)
+	if err2 != nil {
+		t.Fatal("we should acquire slot after the previous one finished")
+	}
+}

internal/queueing/requests.go

+package queueing
+
+import (
+	"net/http"
+	"time"
+
+	"gitlab.com/gitlab-org/gitlab-workhorse/internal/helper"
+)
+
+const DefaultTimeout = 30 * time.Second
+
+func QueueRequests(h http.Handler, limit, queueLimit int, queueTimeout time.Duration) http.Handler {
+	if queueLimit == 0 || limit == 0 {
+		return h
+	}
+	if queueTimeout == 0 {
+		queueTimeout = DefaultTimeout
+	}
+
+	queue := NewQueue(limit, queueLimit)
+
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		err := queue.Acquire(queueTimeout)
+
+		switch err {
+		case nil:
+			defer queue.Release()
+			h.ServeHTTP(w, r)
+
+		case ErrTooManyRequests:
+			helper.TooManyRequests(w, r, err)
+
+		case ErrQueueingTimedout:
+			helper.ServiceUnavailable(w, r, err)
+
+		default:
+			helper.Fail500(w, r, err)
+		}
+
+	})
+}

internal/queueing/requests_test.go

+package queueing_test
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	. "gitlab.com/gitlab-org/gitlab-workhorse/internal/queueing"
+)
+
+var httpHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprintln(w, "OK")
+})
+
+func slowHttpHandler(closeCh chan struct{}) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		<-closeCh
+		fmt.Fprintln(w, "OK")
+	})
+}
+
+func TestQueueRequests(t *testing.T) {
+	w := httptest.NewRecorder()
+	h := QueueRequests(httpHandler, 1, 2, time.Second)
+	h.ServeHTTP(w, nil)
+	if w.Code != 200 {
+		t.Fatal("QueueRequests should process request")
+	}
+}
+
+func testSlowRequestProcessing(count, limit, queueLimit int, queueTimeout time.Duration) *httptest.ResponseRecorder {
+	closeCh := make(chan struct{})
+	defer close(closeCh)
+
+	handler := QueueRequests(slowHttpHandler(closeCh), limit, queueLimit, queueTimeout)
+
+	respCh := make(chan *httptest.ResponseRecorder, count)
+
+	// queue requests to use up the queue
+	for count > 0 {
+		go func() {
+			w := httptest.NewRecorder()
+			handler.ServeHTTP(w, nil)
+			respCh <- w
+		}()
+		count--
+	}
+
+	// dequeue first request
+	return <-respCh
+}
+
+func TestQueueingTimeout(t *testing.T) {
+	w := testSlowRequestProcessing(2, 1, 2, time.Microsecond)
+
+	if w.Code != 503 {
+		t.Fatal("QueueRequests should timeout queued request")
+	}
+}
+
+func TestQueuedRequests(t *testing.T) {
+	w := testSlowRequestProcessing(3, 1, 2, time.Minute)
+
+	if w.Code != 429 {
+		t.Fatal("QueueRequests should return immediately and return too many requests")
+	}
+}

internal/upstream/routes.go

@@ -9,6 +9,7 @@ import (
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/git"
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/lfs"
 	proxypkg "gitlab.com/gitlab-org/gitlab-workhorse/internal/proxy"
+	"gitlab.com/gitlab-org/gitlab-workhorse/internal/queueing"
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/senddata"
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/sendfile"
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/staticpages"
@@ -55,6 +56,7 @@ func (u *Upstream) configureRoutes() {
 		git.SendPatch,
 		artifacts.SendEntry,
 	)
+	apiProxyQueue := queueing.QueueRequests(proxy, u.APILimit, u.APIQueueLimit, u.APIQueueTimeout)
 
 	u.Routes = []route{
 		// Git Clone
@@ -67,8 +69,8 @@ func (u *Upstream) configureRoutes() {
 		route{"POST", regexp.MustCompile(ciAPIPattern + `v1/builds/[0-9]+/artifacts\z`), contentEncodingHandler(artifacts.UploadArtifacts(api, proxy))},
 
 		// Explicitly proxy API requests
-		route{"", regexp.MustCompile(apiPattern), proxy},
-		route{"", regexp.MustCompile(ciAPIPattern), proxy},
+		route{"", regexp.MustCompile(apiPattern), apiProxyQueue},
+		route{"", regexp.MustCompile(ciAPIPattern), apiProxyQueue},
 
 		// Serve assets
 		route{"", regexp.MustCompile(`^/assets/`),

internal/upstream/upstream.go

@@ -20,30 +20,34 @@ import (
 
 var DefaultBackend = helper.URLMustParse("http://localhost:8080")
 
-type Upstream struct {
-	Backend         *url.URL
-	Version         string
-	SecretPath      string
-	DocumentRoot    string
-	DevelopmentMode bool
+type Config struct {
+	Backend             *url.URL
+	Version             string
+	SecretPath          string
+	DocumentRoot        string
+	DevelopmentMode     bool
+	Socket              string
+	ProxyHeadersTimeout time.Duration
+	APILimit            int
+	APIQueueLimit       int
+	APIQueueTimeout     time.Duration
+}
 
+type Upstream struct {
+	Config
 	URLPrefix    urlprefix.Prefix
 	Routes       []route
 	RoundTripper *badgateway.RoundTripper
 }
 
-func NewUpstream(backend *url.URL, socket, version, secretFile, documentRoot string, developmentMode bool, proxyHeadersTimeout time.Duration) *Upstream {
+func NewUpstream(config Config) *Upstream {
 	up := Upstream{
-		Backend:         backend,
-		Version:         version,
-		SecretPath:      secretFile,
-		DocumentRoot:    documentRoot,
-		DevelopmentMode: developmentMode,
+		Config: config,
 	}
-	if backend == nil {
+	if up.Backend == nil {
 		up.Backend = DefaultBackend
 	}
-	up.RoundTripper = badgateway.NewRoundTripper(up.Backend, socket, proxyHeadersTimeout)
+	up.RoundTripper = badgateway.NewRoundTripper(up.Backend, up.Socket, up.ProxyHeadersTimeout)
 	up.configureURLPrefix()
 	up.configureRoutes()
 	return &up

main.go

@@ -24,6 +24,7 @@ import (
 	"syscall"
 	"time"
 
+	"gitlab.com/gitlab-org/gitlab-workhorse/internal/queueing"
 	"gitlab.com/gitlab-org/gitlab-workhorse/internal/upstream"
 )
 
@@ -41,6 +42,9 @@ var documentRoot = flag.String("documentRoot", "public", "Path to static files c
 var proxyHeadersTimeout = flag.Duration("proxyHeadersTimeout", 5*time.Minute, "How long to wait for response headers when proxying the request")
 var developmentMode = flag.Bool("developmentMode", false, "Allow to serve assets from Rails app")
 var secretPath = flag.String("secretPath", "./.gitlab_workhorse_secret", "File with secret key to authenticate with authBackend")
+var apiLimit = flag.Int("apiLimit", 0, "Number of API requests allowed at single time")
+var apiQueueLimit = flag.Int("apiQueueLimit", 0, "Number of API requests allowed to be queued")
+var apiQueueTimeout = flag.Duration("apiQueueDuration", queueing.DefaultTimeout, "Maximum queueing duration of requests")
 
 func main() {
 	flag.Usage = func() {
@@ -89,16 +93,20 @@ func main() {
 		}()
 	}
 
-	up := wrapRaven(
-		upstream.NewUpstream(
-			backendURL,
-			*authSocket,
-			Version,
-			*secretPath,
-			*documentRoot,
-			*developmentMode,
-			*proxyHeadersTimeout,
-		))
+	upConfig := upstream.Config{
+		Backend:             backendURL,
+		Socket:              *authSocket,
+		Version:             Version,
+		SecretPath:          *secretPath,
+		DocumentRoot:        *documentRoot,
+		DevelopmentMode:     *developmentMode,
+		ProxyHeadersTimeout: *proxyHeadersTimeout,
+		APILimit:            *apiLimit,
+		APIQueueLimit:       *apiQueueLimit,
+		APIQueueTimeout:     *apiQueueTimeout,
+	}
+
+	up := wrapRaven(upstream.NewUpstream(upConfig))
 
 	log.Fatal(http.Serve(listener, up))
 }

main_test.go

@@ -868,15 +868,14 @@ func archiveOKServer(t *testing.T, archiveName string) *httptest.Server {
 }
 
 func startWorkhorseServer(authBackend string) *httptest.Server {
-	u := upstream.NewUpstream(
-		helper.URLMustParse(authBackend),
-		"",
-		"123",
-		testhelper.SecretPath(),
-		testDocumentRoot,
-		false,
-		0,
-	)
+	config := upstream.Config{
+		Backend:      helper.URLMustParse(authBackend),
+		Version:      "123",
+		SecretPath:   testhelper.SecretPath(),
+		DocumentRoot: testDocumentRoot,
+	}
+
+	u := upstream.NewUpstream(config)
 	return httptest.NewServer(u)
 }