Fix HTTP challenge router unexpected delayed creation

integration/resources/compose/tlsclientheaders.yml

@@ -1,7 +1,7 @@
 whoami:
     image: traefik/whoami
     labels:
-      - traefik.http.routers.route1.rule=PathPrefix(`/`)
+      - traefik.http.routers.route1.rule=PathPrefix(`/foo`)
       - traefik.http.routers.route1.middlewares=passtls
       - traefik.http.routers.route1.tls=true
       - traefik.http.middlewares.passtls.passtlsclientcert.pem=true

integration/tls_client_headers_test.go

@@ -50,10 +50,10 @@ func (s *TLSClientHeadersSuite) TestTLSClientHeaders(c *check.C) {
 	c.Assert(err, checker.IsNil)
 	defer s.killCmd(cmd)
 
-	err = try.GetRequest("http://127.0.0.1:8080/api/rawdata", 2*time.Second, try.BodyContains("PathPrefix(`/`)"))
+	err = try.GetRequest("http://127.0.0.1:8080/api/rawdata", 2*time.Second, try.BodyContains("PathPrefix(`/foo`)"))
 	c.Assert(err, checker.IsNil)
 
-	request, err := http.NewRequest(http.MethodGet, "https://127.0.0.1:8443", nil)
+	request, err := http.NewRequest(http.MethodGet, "https://127.0.0.1:8443/foo", nil)
 	c.Assert(err, checker.IsNil)
 
 	certificate, err := tls.LoadX509KeyPair(certPemPath, certKeyPath)

pkg/provider/aggregator/aggregator.go

@@ -8,12 +8,14 @@ import (
 	"github.com/traefik/traefik/v2/pkg/log"
 	"github.com/traefik/traefik/v2/pkg/provider"
 	"github.com/traefik/traefik/v2/pkg/provider/file"
+	"github.com/traefik/traefik/v2/pkg/provider/traefik"
 	"github.com/traefik/traefik/v2/pkg/safe"
 )
 
 // ProviderAggregator aggregates providers.
 type ProviderAggregator struct {
-	fileProvider *file.Provider
+	internalProvider provider.Provider
+	fileProvider     provider.Provider
 	providers        []provider.Provider
 }
 
@@ -98,11 +100,15 @@ func (p *ProviderAggregator) AddProvider(provider provider.Provider) error {
 		return err
 	}
 
-	if fileProvider, ok := provider.(*file.Provider); ok {
-		p.fileProvider = fileProvider
-	} else {
+	switch provider.(type) {
+	case *file.Provider:
+		p.fileProvider = provider
+	case *traefik.Provider:
+		p.internalProvider = provider
+	default:
 		p.providers = append(p.providers, provider)
 	}
+
 	return nil
 }
 
@@ -117,12 +123,17 @@ func (p ProviderAggregator) Provide(configurationChan chan<- dynamic.Message, po
 		launchProvider(configurationChan, pool, p.fileProvider)
 	}
 
+	if p.internalProvider != nil {
+		launchProvider(configurationChan, pool, p.internalProvider)
+	}
+
 	for _, prd := range p.providers {
 		prd := prd
 		safe.Go(func() {
 			launchProvider(configurationChan, pool, prd)
 		})
 	}
+
 	return nil
 }
 

pkg/provider/aggregator/aggregator_test.go

@@ -0,0 +1,79 @@
+package aggregator
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v2/pkg/config/dynamic"
+	"github.com/traefik/traefik/v2/pkg/provider"
+	"github.com/traefik/traefik/v2/pkg/safe"
+)
+
+func TestProviderAggregator_Provide(t *testing.T) {
+	aggregator := ProviderAggregator{
+		internalProvider: &providerMock{"internal"},
+		fileProvider:     &providerMock{"file"},
+		providers: []provider.Provider{
+			&providerMock{"salad"},
+			&providerMock{"tomato"},
+			&providerMock{"onion"},
+		},
+	}
+
+	cfgCh := make(chan dynamic.Message)
+	errCh := make(chan error)
+	pool := safe.NewPool(context.Background())
+
+	t.Cleanup(pool.Stop)
+
+	go func() {
+		errCh <- aggregator.Provide(cfgCh, pool)
+	}()
+
+	// Make sure the file provider is always called first, followed by the internal provider.
+	requireReceivedMessageFromProviders(t, cfgCh, []string{"file"})
+	requireReceivedMessageFromProviders(t, cfgCh, []string{"internal"})
+
+	// Check if all providers have been called, the order doesn't matter.
+	requireReceivedMessageFromProviders(t, cfgCh, []string{"salad", "tomato", "onion"})
+
+	require.NoError(t, <-errCh)
+}
+
+// requireReceivedMessageFromProviders makes sure the given providers have emitted a message on the given message channel.
+// Providers order is not enforced.
+func requireReceivedMessageFromProviders(t *testing.T, cfgCh <-chan dynamic.Message, names []string) {
+	t.Helper()
+
+	var msg dynamic.Message
+	var receivedMessagesFrom []string
+
+	for range names {
+		select {
+		case <-time.After(10 * time.Millisecond):
+		case msg = <-cfgCh:
+			receivedMessagesFrom = append(receivedMessagesFrom, msg.ProviderName)
+		}
+	}
+
+	require.ElementsMatch(t, names, receivedMessagesFrom)
+}
+
+type providerMock struct {
+	Name string
+}
+
+func (p *providerMock) Init() error {
+	return nil
+}
+
+func (p *providerMock) Provide(configurationChan chan<- dynamic.Message, pool *safe.Pool) error {
+	configurationChan <- dynamic.Message{
+		ProviderName:  p.Name,
+		Configuration: &dynamic.Configuration{},
+	}
+
+	return nil
+}