respond with 503 on empty backend

integration/healthcheck_test.go

@@ -59,8 +59,8 @@ func (s *HealthCheckSuite) TestSimpleConfiguration(c *check.C) {
 	// Waiting for Traefik healthcheck
 	try.Sleep(2 * time.Second)
 
-	// Verify frontend health : 500
-	err = try.Request(frontendHealthReq, 3*time.Second, try.StatusCodeIs(http.StatusInternalServerError))
+	// Verify no backend service is available due to failing health checks
+	err = try.Request(frontendHealthReq, 3*time.Second, try.StatusCodeIs(http.StatusServiceUnavailable))
 	c.Assert(err, checker.IsNil)
 
 	// Change one whoami health to 200
@@ -77,7 +77,7 @@ func (s *HealthCheckSuite) TestSimpleConfiguration(c *check.C) {
 	c.Assert(err, checker.IsNil)
 	frontendReq.Host = "test.localhost"
 
-	// Check if whoami1 respond
+	// Check if whoami1 responds
 	err = try.Request(frontendReq, 500*time.Millisecond, try.BodyContains(whoami1Host))
 	c.Assert(err, checker.IsNil)
 

middlewares/empty_backend_handler.go

@@ -0,0 +1,31 @@
+package middlewares
+
+import (
+	"net/http"
+
+	"github.com/containous/traefik/healthcheck"
+)
+
+// EmptyBackendHandler is a middlware that checks whether the current Backend
+// has at least one active Server in respect to the healthchecks and if this
+// is not the case, it will stop the middleware chain and respond with 503.
+type EmptyBackendHandler struct {
+	lb   healthcheck.LoadBalancer
+	next http.Handler
+}
+
+// NewEmptyBackendHandler creates a new EmptyBackendHandler instance.
+func NewEmptyBackendHandler(lb healthcheck.LoadBalancer, next http.Handler) *EmptyBackendHandler {
+	return &EmptyBackendHandler{lb: lb, next: next}
+}
+
+// ServeHTTP responds with 503 when there is no active Server and otherwise
+// invokes the next handler in the middleware chain.
+func (h *EmptyBackendHandler) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
+	if len(h.lb.Servers()) == 0 {
+		rw.WriteHeader(http.StatusServiceUnavailable)
+		rw.Write([]byte(http.StatusText(http.StatusServiceUnavailable)))
+	} else {
+		h.next.ServeHTTP(rw, r)
+	}
+}

middlewares/empty_backend_handler_test.go

@@ -0,0 +1,70 @@
+package middlewares
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+
+	"github.com/containous/traefik/testhelpers"
+	"github.com/vulcand/oxy/roundrobin"
+)
+
+func TestEmptyBackendHandler(t *testing.T) {
+	tests := []struct {
+		amountServer   int
+		wantStatusCode int
+	}{
+		{
+			amountServer:   0,
+			wantStatusCode: http.StatusServiceUnavailable,
+		},
+		{
+			amountServer:   1,
+			wantStatusCode: http.StatusOK,
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+
+		t.Run(fmt.Sprintf("amount servers %d", test.amountServer), func(t *testing.T) {
+			t.Parallel()
+
+			nextHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusOK)
+			})
+			handler := NewEmptyBackendHandler(&healthCheckLoadBalancer{test.amountServer}, nextHandler)
+
+			recorder := httptest.NewRecorder()
+			req := httptest.NewRequest(http.MethodGet, "http://localhost", nil)
+
+			handler.ServeHTTP(recorder, req)
+
+			if recorder.Result().StatusCode != test.wantStatusCode {
+				t.Errorf("Received status code %d, wanted %d", recorder.Result().StatusCode, test.wantStatusCode)
+			}
+		})
+	}
+}
+
+type healthCheckLoadBalancer struct {
+	amountServer int
+}
+
+func (lb *healthCheckLoadBalancer) RemoveServer(u *url.URL) error {
+	return nil
+}
+
+func (lb *healthCheckLoadBalancer) UpsertServer(u *url.URL, options ...roundrobin.ServerOption) error {
+	return nil
+}
+
+func (lb *healthCheckLoadBalancer) Servers() []*url.URL {
+	servers := make([]*url.URL, lb.amountServer)
+	for i := 0; i < lb.amountServer; i++ {
+		servers = append(servers, testhelpers.MustParseURL("http://localhost"))
+	}
+	return servers
+}

server/server.go

@@ -744,6 +744,7 @@ func (server *Server) loadConfig(configurations configs, globalConfiguration Glo
 							log.Debugf("Setting up backend health check %s", *hcOpts)
 							backendsHealthcheck[frontend.Backend] = healthcheck.NewBackendHealthCheck(*hcOpts)
 						}
+						lb = middlewares.NewEmptyBackendHandler(rebalancer, lb)
 					case types.Wrr:
 						log.Debugf("Creating load-balancer wrr")
 						if stickysession {
@@ -764,6 +765,7 @@ func (server *Server) loadConfig(configurations configs, globalConfiguration Glo
 							log.Debugf("Setting up backend health check %s", *hcOpts)
 							backendsHealthcheck[frontend.Backend] = healthcheck.NewBackendHealthCheck(*hcOpts)
 						}
+						lb = middlewares.NewEmptyBackendHandler(rr, lb)
 					}
 
 					if len(frontend.Errors) > 0 {

server/server_test.go

@@ -3,6 +3,7 @@ package server
 import (
 	"fmt"
 	"net/http"
+	"net/http/httptest"
 	"net/url"
 	"reflect"
 	"testing"
@@ -576,3 +577,171 @@ func TestServerEntrypointWhitelistConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestServerResponseEmptyBackend(t *testing.T) {
+	const requestPath = "/path"
+	const routeRule = "Path:" + requestPath
+
+	testCases := []struct {
+		desc           string
+		dynamicConfig  func(testServerURL string) *types.Configuration
+		wantStatusCode int
+	}{
+		{
+			desc: "Ok",
+			dynamicConfig: func(testServerURL string) *types.Configuration {
+				return buildDynamicConfig(
+					withFrontend("frontend", buildFrontend(withRoute(requestPath, routeRule))),
+					withBackend("backend", buildBackend(withServer("testServer", testServerURL))),
+				)
+			},
+			wantStatusCode: http.StatusOK,
+		},
+		{
+			desc: "No Frontend",
+			dynamicConfig: func(testServerURL string) *types.Configuration {
+				return buildDynamicConfig()
+			},
+			wantStatusCode: http.StatusNotFound,
+		},
+		{
+			desc: "Empty Backend LB-Drr",
+			dynamicConfig: func(testServerURL string) *types.Configuration {
+				return buildDynamicConfig(
+					withFrontend("frontend", buildFrontend(withRoute(requestPath, routeRule))),
+					withBackend("backend", buildBackend(withLoadBalancer("Drr", false))),
+				)
+			},
+			wantStatusCode: http.StatusServiceUnavailable,
+		},
+		{
+			desc: "Empty Backend LB-Drr Sticky",
+			dynamicConfig: func(testServerURL string) *types.Configuration {
+				return buildDynamicConfig(
+					withFrontend("frontend", buildFrontend(withRoute(requestPath, routeRule))),
+					withBackend("backend", buildBackend(withLoadBalancer("Drr", true))),
+				)
+			},
+			wantStatusCode: http.StatusServiceUnavailable,
+		},
+		{
+			desc: "Empty Backend LB-Wrr",
+			dynamicConfig: func(testServerURL string) *types.Configuration {
+				return buildDynamicConfig(
+					withFrontend("frontend", buildFrontend(withRoute(requestPath, routeRule))),
+					withBackend("backend", buildBackend(withLoadBalancer("Wrr", false))),
+				)
+			},
+			wantStatusCode: http.StatusServiceUnavailable,
+		},
+		{
+			desc: "Empty Backend LB-Wrr Sticky",
+			dynamicConfig: func(testServerURL string) *types.Configuration {
+				return buildDynamicConfig(
+					withFrontend("frontend", buildFrontend(withRoute(requestPath, routeRule))),
+					withBackend("backend", buildBackend(withLoadBalancer("Wrr", true))),
+				)
+			},
+			wantStatusCode: http.StatusServiceUnavailable,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			testServer := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				rw.WriteHeader(http.StatusOK)
+			}))
+			defer testServer.Close()
+
+			globalConfig := GlobalConfiguration{
+				EntryPoints: EntryPoints{
+					"http": &EntryPoint{},
+				},
+			}
+			dynamicConfigs := configs{"config": test.dynamicConfig(testServer.URL)}
+
+			srv := NewServer(globalConfig)
+			entryPoints, err := srv.loadConfig(dynamicConfigs, globalConfig)
+			if err != nil {
+				t.Fatalf("error loading config: %s", err)
+			}
+
+			responseRecorder := &httptest.ResponseRecorder{}
+			request := httptest.NewRequest(http.MethodGet, testServer.URL+requestPath, nil)
+
+			entryPoints["http"].httpRouter.ServeHTTP(responseRecorder, request)
+
+			if responseRecorder.Result().StatusCode != test.wantStatusCode {
+				t.Errorf("got status code %d, want %d", responseRecorder.Result().StatusCode, test.wantStatusCode)
+			}
+		})
+	}
+}
+
+func buildDynamicConfig(dynamicConfigBuilders ...func(*types.Configuration)) *types.Configuration {
+	config := &types.Configuration{
+		Frontends: make(map[string]*types.Frontend),
+		Backends:  make(map[string]*types.Backend),
+	}
+	for _, build := range dynamicConfigBuilders {
+		build(config)
+	}
+	return config
+}
+
+func withFrontend(frontendName string, frontend *types.Frontend) func(*types.Configuration) {
+	return func(config *types.Configuration) {
+		config.Frontends[frontendName] = frontend
+	}
+}
+
+func withBackend(backendName string, backend *types.Backend) func(*types.Configuration) {
+	return func(config *types.Configuration) {
+		config.Backends[backendName] = backend
+	}
+}
+
+func buildFrontend(frontendBuilders ...func(*types.Frontend)) *types.Frontend {
+	fe := &types.Frontend{
+		EntryPoints: []string{"http"},
+		Backend:     "backend",
+		Routes:      make(map[string]types.Route),
+	}
+	for _, build := range frontendBuilders {
+		build(fe)
+	}
+	return fe
+}
+
+func withRoute(routeName, rule string) func(*types.Frontend) {
+	return func(fe *types.Frontend) {
+		fe.Routes[routeName] = types.Route{Rule: rule}
+	}
+}
+
+func buildBackend(backendBuilders ...func(*types.Backend)) *types.Backend {
+	be := &types.Backend{
+		Servers:      make(map[string]types.Server),
+		LoadBalancer: &types.LoadBalancer{Method: "Wrr"},
+	}
+	for _, build := range backendBuilders {
+		build(be)
+	}
+	return be
+}
+
+func withServer(name, url string) func(backend *types.Backend) {
+	return func(be *types.Backend) {
+		be.Servers[name] = types.Server{URL: url}
+	}
+}
+
+func withLoadBalancer(method string, sticky bool) func(*types.Backend) {
+	return func(be *types.Backend) {
+		be.LoadBalancer = &types.LoadBalancer{Method: method, Sticky: sticky}
+	}
+}