Improve handling of failing dns resolvers

resolver/resolve.go

@@ -302,18 +302,16 @@ resolveLoop:
 					// we are offline and this is not an online check query
 					return nil, ErrOffline
 				default:
+					// includes ErrTimeout
 					log.Tracer(ctx).Debugf("resolver: failed to resolve %s: %s", q.FQDN, err)
 				}
-			} else {
-				// no error
+			}
 			if rrCache == nil {
-					// defensive: assume NXDomain
-					return nil, ErrNotFound
+				continue
 			}
 			break resolveLoop
 		}
 	}
-	}
 
 	// check for error
 	if err != nil {

resolver/resolver.go

@@ -28,7 +28,7 @@ const (
 
 var (
 	// FailThreshold is amount of errors a resolvers must experience in order to be regarded as failed.
-	FailThreshold = 5
+	FailThreshold = 20
 )
 
 // Resolver holds information about an active resolver.