Add errors about unknown entryPoint in runtime api

pkg/config/runtime/runtime_http.go

@@ -2,6 +2,7 @@ package runtime
 
 import (
 	"context"
+	"fmt"
 	"sync"
 
 	"github.com/containous/traefik/v2/pkg/config/dynamic"
@@ -17,23 +18,32 @@ func (c *Configuration) GetRoutersByEntryPoints(ctx context.Context, entryPoints
 			continue
 		}
 
+		logger := log.FromContext(log.With(ctx, log.Str(log.RouterName, rtName)))
 		eps := rt.EntryPoints
 		if len(eps) == 0 {
+			logger.Debugf("No entrypoint defined for this router, using the default one(s) instead: %+v", entryPoints)
 			eps = entryPoints
 		}
+		entryPointsCount := 0
 		for _, entryPointName := range eps {
 			if !contains(entryPoints, entryPointName) {
-				log.FromContext(log.With(ctx, log.Str(log.EntryPointName, entryPointName))).
+				rt.AddError(fmt.Errorf("entryPoint %q doesn't exist", entryPointName), false)
+				logger.WithField(log.EntryPointName, entryPointName).
 					Errorf("entryPoint %q doesn't exist", entryPointName)
 				continue
 			}
 
+			entryPointsCount++
 			if _, ok := entryPointsRouters[entryPointName]; !ok {
 				entryPointsRouters[entryPointName] = make(map[string]*RouterInfo)
 			}
 
 			entryPointsRouters[entryPointName][rtName] = rt
 		}
+		if entryPointsCount == 0 {
+			rt.AddError(fmt.Errorf("no valid entryPoint for this router"), true)
+			logger.Error("no valid entryPoint for this router")
+		}
 	}
 
 	return entryPointsRouters