[gateway] quiet per-translation log spam in HTTPRoute processing

The shared backplane re-runs a full Gateway-API translation every few
seconds, and each pass logged an Info line per HTTP filter plus a
spurious "No valid HTTP backends" Error for every DirectResponse-backed
route (which legitimately has no backendRefs). Together these accounted
for ~3 log events/s per edge cluster and pushed the staging namespace
into Vector's per-namespace ingest cap.

Demote the per-filter line to Debug and only log the no-valid-backends
error when the translator actually injects the 500 fallback.

Author: dilyevsky

pkg/gateway/gatewayapi/filters.go

@@ -74,7 +74,7 @@ func (t *Translator) ProcessHTTPFilters(parentRef *RouteParentContext,
 	}
 	for i := range filters {
 		filter := filters[i]
-		log.Infof("Processing HTTP filter: %s", filter.Type)
+		log.Debugf("Processing HTTP filter: %s", filter.Type)
 		// If an invalid filter type has been configured then skip processing any more filters
 		if httpFiltersContext.DirectResponse != nil {
 			log.Warnf("Skipping processing of HTTP filters as a DirectResponse has been configured")

pkg/gateway/gatewayapi/route.go

@@ -269,13 +269,14 @@ func (t *Translator) processHTTPRouteRules(httpRoute *HTTPRouteContext, parentRe
 		// If the route has no valid backends then just use a direct response and don't fuss with weighted responses
 		for _, ruleRoute := range ruleRoutes {
 			noValidBackends := ruleRoute.Destination == nil || ruleRoute.Destination.ToBackendWeights().Valid == 0
-			if noValidBackends && ruleRoute.Redirect == nil {
+			// A route that already carries a DirectResponse (e.g. from a
+			// DirectResponse extension filter) legitimately has no backends,
+			// so only complain when we have to inject the 500 fallback.
+			if noValidBackends && ruleRoute.Redirect == nil && ruleRoute.DirectResponse == nil {
 				log.Errorf("No valid HTTP backends for route %s: destination=%v", ruleRoute.Name, ruleRoute.Destination)
-				if ruleRoute.DirectResponse == nil {
-					ruleRoute.DirectResponse = &ir.DirectResponse{
-						StatusCode: 500,
-						Body:       ptr.To("no valid HTTP backends"),
-					}
+				ruleRoute.DirectResponse = &ir.DirectResponse{
+					StatusCode: 500,
+					Body:       ptr.To("no valid HTTP backends"),
 				}
 			}
 			ruleRoute.IsHTTP2 = false