respond with 503 on empty backend

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
+}